3. Mechanical Properties
CONTENTS
1. INTRODUCTION
2. STRESS-STRAIN CURVE
3. SHORT TERM MECHANICAL PROPERTIES
3.1 Tensile Properties
3.2 Flexural Properties
3.3 Impact Properties
3.4 Compressive Properties
3.5 Shear Strength
3.6 Tear Strength
A. Initiation
B. Propagation
3.7 Stiffness Test
3.8 Burst Strength
A. Long- term method
B. Short- term method
4. LONG TERM PROPERTIES
4.1 Creep Properties
4.2 Stress Relaxation
4.3 Fatigue Resistance
5. SURFACE PROPERTIES
5.1 Abrasion Resistance.
A. Transparent Plastics
B. Flat specimens
5.2 Hardness Test
5.3 Co-efficient of Friction
Topics Covered
1. Introduction
2. Definition
3. Significance
4. Test Method
5. Specimen Preparation and Condition
6. Test Procedure
7. Observation / Calculation/Result
8. Formula
9. Factors Influencing
10. Test Results
11. Safety Precautions
12. References
1. INTRODUCTION
The mechanical properties are the most important properties because all service
conditions and the majority of end-use applications in involve some degree of mechanical
loading. The material selection for a variety of applications is quite often based on mechanical
properties such as tensile strength, modulus, elongation and impact strength. Although the
voluminous data on these engineering properties are available, this is still not sufficient in view
of the rapid development of new polymers and their formulations. Available data on
mechanical properties are not sufficient for material selection since these are dependent on
temperature, humidity, time, loading conditions, rate of loading etc.
The mechanical properties of plastics can be broadly classified as short-term,
long-term and surface properties. The short-term properties are measured at a constant rate of
stress or strain different modes like tension, compression, flexural, shear etc. The long-term
properties are measurements of deformation or stress decay with respect to time in static
conditions e.g. creep and stress relaxation.
The mechanical properties such as tensile strength, modulus, elongation and
impact strength are normally derived from the technical literature. Definition of these
properties are as follows:
a) Stress: The force applied to produce deformation in a unit area of a test specimen.
Stress is a ratio of applied load to the original cross sectional area expressed in lbs/in2.
b) Strain:
The ratio of elongation to the gauge length of the test specimen, or simply
stated, change in length per unit of the original length. It is expressed as the dimensionless
quantity.
c) Gauge Length: The original length between two marks on the test piece over which
the change in length is determined.
d)
Percentage Elongation: The increase in the length of a specimen produced by a
tensile load.
e) Percentage Elongation at Yield: The percentage elongation produced in the gauge
length of the test piece at the yield stress.
f)
Percentage Elongation at break, or at maximum load: The elongation at break, or at
maximum load, produced in the gauge length of the test piece, expressed as a percentage of
the gauge length. a)
g) Elongation: The increase in the length of a specimen produced by a tensile load.
h) Yield point: The first point of stress-strain curve at which an increase the strain occurs
without the increase in stress.
i) Yield strength: The stress at which a material exhibits a specified limiting deviation
from the proportionality of stress to strain.
j) Proportional limit: The greatest stress at which a material is capable of sustaining the
applied load without any deviation from proportionality of stress to strain.
k) Elastic Modulus in tension (Young’s modulus):
The ratio of tensile stress to
corresponding strain below the proportional limit. The stress-strain relationship of many
plastics does not conform to Hooke’s law throughout the elastics range but deviates their
form even at stress well below the yield stress. For such materials the slope of the tangent
to the stress-strain curve at low strain is usually taken as the elastic modulus.
l) Secant modulus: The ratio of total stress to corresponding strain at any specific point
on the stress-strain curve. It is also expressed in F/A ‘or’ lb/in2
2. STRESS – STRAIN CURVE
STRESS – STRAIN CURVE: The mechanical behavior of plastics is defined by using the
stress-strain curve obtained in different modes like tension, flexure, compression or shear. The
curves obtained in different loading conditions broadly resemble each other. Typical stress and
strain curve of plastics obtained intension for constant rate of loading is given below in figure 1.
D yield
C
Stress
↓
E
break
B
A
Strain →
A typical stress strain curve
The deformation behavior is summarized in different stages as discussed below:
i) Polymer molecules rest in random fashion in the slid state (A) whereas on initial
application of stress at a constant rate, bending and stretching of interatomic bonds takes
place (A-B). This results in smaller deformation at molecular level. On relieving the stress,
this deformation is recoverable instantaneously.
ii) The stretching of molecules continues from B to C, where in C is ‘proportionality
limit’ as stress is proportional to strain from A to C (Hooke’s law) on relieving the stress,
this anywhere up to the point C deformation is recoverable. This region is known as elastic
behavior of polymer materials. The ratio of stress to strain from A to C gives the value of
Young’s modulus or modulus of elasticity, which indicates the material’s stiffness.
iii) The straightening of molecules continues from C to D but without their slippage.
The molecular deformations in this region are recoverable but not instantaneously. Point D
in the curve is the Yield Point. As material stretches, its dimensions orthogonal to the axis
of applied force decreases, thus the cross-section area decreases. The material thus starts
necking.
iv)
The deformation from D to E takes place without increase in stress.
Strain hardening starts from point E. This hardening of material is a necessary
prerequisite for cold drawing phenomena of material deformation when the rate
of deformation is constant. Molecules slippage and orientation in the direction of
applied stress continuous in E-F region.
The deformation of this nature
determines the viscous behavior of the material and is irrecoverable. At point F
the material fails to withstand the applied stress and breaks.
v)
These three types of deformation do not occur separately but are
superimposed on each other. The bonding & the stretching of the interactive
bonds are almost instantaneous. The molecular uncoiling is relatively slow.
vi)
Area under curve i.e. A to E known as toughness of the material.
Modulus of elasticity indicates the stiffness of the material.
The polymers are broadly classified as per their strain behavior, which is the indication of
softness, brittleness, hardness and toughness. A hard & strong material has high modulus,
high yield stress, usually high ultimate strength & low elongation e.g. acetal. A hard & tough
material characterized by high modulus, high yield stress, high elongation at break & high
ultimate strength Polycarbonate is considered hard & tough material.
Maxwell
Model
Ratio of stress to corresponding strain with in the range of greatest stress that the Maxwell is
capable to sustaining with any deviation of proportionality of stress to strain.
The initial portion of the stress-strain curve between curve point A to C is linear and it
follows Hook’s law, which states that the stress is proportional to the strain. The point at which
the actual curve dewaks from
the straight line is called the Proportional limit, meaning that only upto this point is stress
proportional to strain. The behavior of the plastics material below the proportional limit is elastic
in nature and therefore the deformations are recoverable.
3. 1 TENSILE PROPERTIES
3.1.1 INTRODUCTION
The study of stress in relation to strain in tension depicts the tensile properties of the
material. The tensile elongation and modulus measurements are the most important
indications of strength in a material and are the most widely specified properties of plastics
material. The tensile properties is measurement of the ability of material to with stand forces
that tend to pull it apart and to determine to what extent material stretches before breaking.
Tensile modulus, an indication of the relative stiffness of a material, which is calculated from
a stress-strain curve. Plastics materials are compared on the basis of tensile strength,
elongation and tensile modulus data. These data are useful for the propose of engineering
design and understanding the characteristics of materials. The properties of material changes
by various factors like rate of straining, environmental conditions, the addition of additives
like fillers, Plasticizer etc.
3.1.2 DEFINITION
3.1.2 (a) Tensile strength.
The maximum Tensile stress ( nominal) sustained by a test piece during a tension test or
Ultimate strength of a material subjected to tensile loading otherwise, it is a measurement of
the ability of a material to withstand forces that to pull it apart and to determine to what extent
the material stretches before breaking.
3.1.2 (b) Tensile Modulus
The ratio of tensile stress to corresponding strain at the maximum load. It is an indication of
the relative stiffness of a material.
3.1.2(c) Percentage of Elongation at Yield
The percentage elongation produced in the gauge length of the test piece at the yield tensile
stress.
3.1.2(d) Percentage of Elongation at Break
The elongation at break, or at maximum load, produced in the gauge length of the test piece,
expressed as a percentage of the gauge length.
UNITS:
Tensile strength / Modulus = Kgf/cm2
Percentage of Elongation = %
3.1.3 SIGNIFICANCE:
(1) This test method is designed to produce tensile property data for the control and
specification of plastics materials. These data are also useful for qualitative
characterization purpose and for research and development. .
(2)
Tensile properties may provide useful data for plastics engineering design
purposes. However, because of the high degree of sensitivity exhibited by many
plastics to rate at straining and environmental conditions.
3.1.4 TEST METHOD:
A) Standard Test Method for Tensile Properties of Plastics (ASTM D 638),
IS-8453, JIS-7113, ISO-1184, BS-2782
3.1.5 TEST SPECIMEN: -
“Dumb-bell shaped”
3.1.5(a) Dimensions of Test Specimen:
Test specimen dimensions vary considerably depending upon the requirements and also
various types of materials used.
Tensile test piece ISO / DIS 527 Type 1(Broad-waisted Dumb-bell)
T= 1min, =10 max, =4preferred, = 4for molded test pieces
(Dimension in millimeters)
Tensile test piece ISO / DIS 527 Type 2 (Narrow-waisted Dumb-bell)
T= 1 min, =3 max, =2 preferred (Dimension in millimeters)
Tensile test piece ISO / DIS 527 Type 3(Dug-Bone Dumbbell)
(Dimension in millimeters)
3.1.5 (b) Specimen Preparation Methods:
Film - cutting punch & punching machine.
Sheet - contour cutting machine.
Foam - cutting& punching machine.
Liquid - coating & casting process
Thermoset – Compression molding machine, Injection molding machine,
Transfer molding machine.
Thermoplastic - Compression molding machine, Injection molding machine.
3.1.5 (c) CONDITIONING OF TEST SPECIMENS:
Condition the test specimens at 23 ± 2°C and 50 ± 5% or 27 ± 2°C and 65 ± 5% relative
humidity for not less than 40 hours prior to test in accordance with procedure as per
ASTM D 618.
3.1.5(d) TEST ATMOSPHERE:
Conduct tests in the standard laboratory atmosphere of 23 ± 2°C and 50 ± 5% relative
humidity unless otherwise specified in the test methods. In cases of disagreements, the
tolerances are ± 1°C and ± 2% relative humidity.
3.1.6 EQUIPMENT/ INSTRUMENTS DETAILS:
(1) Testing machine consists of
(a) Fixed member
(b) Movable member
(c) Grips
(d) Drive mechanism
(e) Load indicator
(2) Extension Indicator
(a) Modulus of elasticity measurements
(b) Low extension measurements
(c) High extension measurements
(d) Micrometers
3.1.6 (a) EQUIPMENT:
The tensile testing machine is a device for applying force onto the test specimen coupled to
means of measuring the force and extension. The tensile machine of a constant rate of
crosshead movement is used. It has a fixed or stationary member carrying one grip, and a
movable member carrying a second grip with variable speed control is employed for the
testing. The grips for holding the test specimen between the fixed and movable member
should be self aligning and move freely, so that the long axis of the text specimen will
coincide with the direction of the applied pull through the center line of the grip assembly.
Universal testing machine for testing of the specimen in either Tension or compression
Universal testing machine for testing of the specimen in either Tension or compression
3.1.6 (b) GRIPS:
Different types of grips used for tensile testing are given below.

Wedge action type grip - It is suitable for rigid flat sheeting.
Wedge action grips
•Grip for molded thermoset - It is suitable for thermoset materials.
Gribs for molded parts
•
Vice Type Chucks Grip – It is suitable for thin brittle films.
Vice Type Chucks
 Strip Chucks Grip – It is suitable for vary strong laminates and sheet materials.
 Self Tightening Jaws Grip- It is suitable for soft rubber and plastics sheeting for example
Plasticised PVC.
3.1.6(c) FORCE MEASUREMENTS:
Force measurement in tensile testing machine is carried out with the help of load
cells of variable range like 1-1000KN.There are a number of ways in which load cells are
constructed with many variations on the basic themes. Two common methods are proof ring
and Strain Gauge Bridge. A proof ring depends on the measurement of an extremely small
deformation of a stiff but perfectly elastic metal member by a suitable electrical transducer.
A strain gauge bridge consists of four resistive elements, three of which are fixed
resistors of high stability and the fourth is the measuring element, which is rigidly mounted
on a plate in the load cell body such that as the force is applied and the load cell deforms, it
distorts the measuring elements.
Proof Ring
Strain Gauge
3.1.6(d) ELONGATION MEASUREMENTS:
The requirement for measuring elongation in highly extensible materials gives various grades of
extensometer with differing degree of precision. The accuracy requirement range from ± 1mm
down to ± 0.05mm. These are two types one is Contact & Non contact type. The contact types
rely on the physical contact between extensometer and the specimen to sense the change in length
during test. Non contact extensometer light being are used to track the movement of contrasting
color gauge marks on the test piece, servomechanisms is used to drive the optical heads in the
appropriate direction.
Extensometer attached to the specimen
3.1.7 TEST PROCEDURE:

Accurate measurement of width and thickness of the test specimen in the narrow
parallel portion at several places to the nearest 0.025mm. The gauge length on the specimen
is marked appropriately according to the according to the test standard.

Fixing the specimen between the grips of the machine while maintaining the alignment.

The suitable extensometer is attached to measure extension.

Selection of the lowest test speed that is produced rupture in ½ to 5 min. the speed is
the relative rate of motion of the grips during the test.
Speed of testing 5± 25%, 50±10% & 500±10% for rigid and semi Rigid material where
as 50±10% & 500±10% for non-rigid materials.
Speed of testing is calculated from the required initial strain rate. The rate of grip
separation is determined from the initial strain rates as follows.
A = BC
A= Rate of grip separation, mm/min.
B= Initial distance between grips (in case of film/sheet) or gauge length (in case of dumbbells)
C= Initial strain rate, mm/mm. min.
 Speed is selected according to recorder response and resolution in order to determine
modulus.
 The load – extension curve is recorded.
 Using the load value at any point on the load-extension curve tensile strength is
calculated by dividing the cross – sectional area. In case of tensile strength at yield and at
break, corresponding load values are used from curve for the calculation.
 The elongation of the specimen as dumbbells is measured with reference to the
deformation/extension between the gauge marks. Elongation at break and at yield is
calculated by using the corresponding length of test specimen at that point .
 The tensile modulus is calculated by using strain values derived from the curve at the
maximum stress value.
3.1.9 FORMULA AND CALCULATIONS:
Force (load) (N)
(1) Tensile strength =
Cross-section area of the specimen (mm²)
Maximum load recorded (N)
(2) Tensile strength at yield (N/mm²) =
Cross section area (mm²)
Load recorded at break (N)
(3) Tensile strength at break (N/mm²) =
Cross section area (mm²)
Difference in stress
(4) Tensile Modulus =
Difference in corresponding strain
Change in length (elongation)
(5) Elongation at yield, Strain (ε) =
Original length (gauge length)
(6) Percent Elongation = ε x 100
If the specimen gives a yield load that is larger than the load at break, calculate “percent
elongation at yield” otherwise; calculate “percent elongation at break”.
3.1.10 FACTORS INFLUENCING:
a) Temperature and Humidity –Recommended Temperature and Humidity is 23oC and 55 –65 %.
Tensile Strength decreases as Temperature increases. Moisture works as plasticizer, so it causes
then decrease in Tensile Strength and increase the Elongation.
Environmental test chamber to study tensile properties at different temperature
b) Test Speed – 0.05 mm/min. to 500mm/min. Elongation is high when Test Speed is
minimum i.e. 0.05 mm/min and is lower when Test Speed is maximum i.e. 500 mm/min.
c) Method of specimen Preparation – Molecular Orientation has a significant effect on tensile
Strength values. A load-applied parallel to the direction of molecular orientation may yield
higher value than the load applied perpendicular to the orientation. The opposite is true for
elongation.
d) Effect of Plasticizer and filler – Soften the material, brings down the Tensile Strength and
increase Elongation.
e) Crystallinity – With the increase of Crystallinity, Tensile Strength increases.
f) Rate of Straining- As the strain rate increases, Tensile Strength and modulus increases.
Elongation is inversely proportional to the strain rate.
g) Molecular Weight and Molecular Weight Distribution – With increase in molecular weight,
Tensile Strength also increases. Smaller molecules in polymer work as plasticizer. So with
increase of Molecular Weight Distribution, Elongation decrease and Tensile Strength increases.
The effect of fiberglass orientation
3.1.11. TEST RESULTS:
The report shall include the following:
a) Speed of testing
b) Tensile strength at yield or break, average value, and standard deviation,
c) Tensile stress at yield or break if applicable, average value, and standard deviation,
d) Percent elongation at yield
e) Modulus of elasticity average
3.1.12 SAFETY PRECAUTIONS:
1. Specimen is fix in grips proper tightly.
2. Observation should read carefully.
3. Specimen is clamped vertically
4. Before test, test specimen is checked properly for any moulding or machining defects
3.1.14 REFERENCES: ASTM Standards
D 229 methods of testing rigid sheet and plate materials used for electrical insulation
D 618 methods of conditioning plastics and electrical insulating materials
D 638 test method for tensile properties of plastics
D 651 test method for tensile strength of molded electrical insulating materials
D 882 test methods for tensile properties of thin plastic sheeting
D 883 definition of terms relating to plastics
D 3039 test methods for tensile properties of fiber resin composites
D 4066 specification for nylon injection and extrusion materials.
3.2 FLEXURAL PROPERTIES
3.2.1 INTRODUCTION:
These test methods cover the determination of flexural
properties of unreinforced and reinforced plastics, including high-modulus composites
and electrical insulating material in the form of rectangular bars molded directly or cut
from sheets, plates, or molded shapes. These test methods are generally applicable to rigid
and semi-rigid materials. However, flexible strength cannot be determined for those
materials that do not break or that do not fail in the outer fiber.
Two test methods are describes are as follows:
(i) Test method 1: A three point leading system utilizing central leading on a simply
Supported beam
(ii) Test method 2: A four point leading system utilizing two load equally spaced from
their adjacent support points with a distance between load points of either 1/3 or 1/2 of the
support span.
3.2.2 DEFINITION:
3.2.2(a) Flexural Strength
Flexural strength is the ability of the material to withstand bending forces applied
perpendicular to its longitudinal axis. The stresses induced due to the flexural load are a
combination of compressive and tensile stresses.
3.2.2(b) Flexural Modulus
Within the elastic limit, the ratio of the applied stress on a test specimen in flexure
to the corresponding strain in the outermost fiber of the specimen. Flexural modulus is the
measure of relative stiffness.
Unit-Kg/cm2
3.2.3 SIGNIFICANCE:
1. Flexural properties determined by test method ‘1’ are especially useful for quality Control
and specification purposes.
2. Materials do not fail at the points of maximum stress under test method ‘1’ is test by test
method ‘2’. Flexural properties are determined by second method, are also useful for quality
control and specification purposes. The basic difference between the two types of method is
the location of maximum bending moment and maximum axial fiber stress.
3.2.4 TEST METHOD:
Flexural properties of unreinforced & reinforced plastics & Electrical Insulating
materials (ASTM-D-790), JIS-7203-1982, BS-2782.
3.2.5 TEST SPECIMEN
3.2.5 (a) Specimen Preparation Method
The specimen uses for flexural testing are bars of rectangular cross sections and are cut
from sheets, plates or molded shapes. The common practice is to mold the specimens to
the desired finished dimensions.
3.2.5 (b) Dimensions of Test Specimen
The specimens of size 1/8 x ½ x 4 in. are the most commonly used.
3.2.6 EQUIPMENT DETAILS:
(i) Testing machine: A properly calibrated testing machine that is operated at constant
rate of cross- head motion over the range indicated and in which the error in the load
measuring system shall not exceed ± 1% of maximum load expected to the measured.
(ii) Noses & supports: The loading noses and supports shall have cylindrical surfaces
in order to avoid excessive indentation, or failure due to stress conc. Directly under the
loading noses, the radius of noses and supports are atleast 3mm for all specimens.
3.2.7 TEST PROCEDURE:
 Keep the rectangular specimen horizontally in the stationary crosshead surface.
 The movable portion having the bending nose
 The test is initiated by applying the load to the specimen at the specified crosshead rate.
 The deflection is measured either by a gauge under the specimen in contact with it in
the center of the support span or by measurement of the motion of the loading nose relative
to the supports.
 There are two test methods to conduct the test,
3.2.7(a) Method I: It is a three-point loading system utilizing center loading on a simple
supported beam. A bar of rectangular cross section rest on two supports & is loaded by means of
a loading nose midway between the support the maximum axial fiber stresses occur on a line
under loading nose.
Force involved in bending a simple beam
Close-up of a specimen shown in flexural testing apparatus
3.2.7(b) Method II: It is four -point loading system utilizing two load points equally spaced
from their adjacent supports point, with a distance between load points of one-third of the support
span. In this method, the test bar rests on two supports & is loaded at two point (by means of two
loading noses), each on equal distance from the adjacent support point. This method is very
useful in testing materials that do not fail at the point of maximum stress under a three-point
loading system the maximum axial fiber stress occurs over the area between the loading noses.
Schematic of specimen arrangement for flexural testing
3.2.9 FORMULA AND CALCULATION:
1)
Calculate the rate of cross-head motion as follows and set the machine for the
calculated rate, or as near as possible to it,
R = Z l2 / 6d
Where,
R = rate of cross-head motion (mm/min)
l = support span (mm)
d = depth of beam (mm)
Z = rate of straining of entire fiber (mm/min)
2) Terminate the test in the maximum strain in the outer fiber has reached 0.05 mm/min. The
deflection at which distortion occurs are calculated by ‘r’ equal to 0.05 mm/min as follows
D= rl2 / 6d
Where,
D = midspan deflection (mm)
r = strain (mm/mm)
l = support span
d = depth of beam (mm)
3) Max.fiber stress- test method ‘1’
S = 3PL / 2 bd2
Where,
S = stress in the outer fiber at midspan (Mpa)
p = load at given point on the load deflection curve(v)
L= support beam (mm)
b= width of beam tested (mm)
d = depth of beam tested in (mm)
4) Maximum fiber stress for beam tested at large support spans-test method ‘1’,
S = (3PL / 2 bd2 ) 1+ 6(D/L)2 – 4(d/l) (D/L)
5) Max.fiber stress-test method ‘2’
S = PL / bd2
For a load span of ½ of the support span
S = 3PL / 4 bd2
6) Maximum fiber stress test method ‘2’ for beam tested at large support span:S = (PL / bd2 ) 1 + (4.70 D2 / L2 – (7.04 Dd / L2 )]
For a span of one-half of the support
Span: S = (3PL / 4bd2 ) * [ 1- (10.91 Dd / L2 ) ]
3.2.10 FACTORS INFLUENCING:
a. Specimen Preparation - Injection Moulded Specimen usually shows a higher flexural value
than a compression Moulded specimen.
b. Temperature - Flexural Strength and Modulus value are inversely proportional with
Temperature.
c. Test Conditions - The strain rate, which depends upon testing speed; specimen thickness and
distance between supports (span) can affect the results. At a given span, Flexural Strength
increases as the specimen thickness is increased. Modulus of a material generally increases with
increasing strain rate.
3.2.11 TEST RESULTS:
The result shall include the following:
(i)
Complete indentation of the material tested.
(ii)
Direction of cutting loading specimens
(iii)
Depth and width of specimen
(iv)
Support span to depth ratio
(v)
Rate of cross head motion
(vi)
Flexural strength and average value and std. Deviation.
(vii)
Flexural yield strength
3.2.13 REFERENCES: ASTM STD.
D 618 Methods of conditioning plastics and electrical insulating materials and
Testing
D 638, this method is used for tensile properties of materials
D 4066, Specification for nylon injection, extrusion materials
E4 Practices for load variation of testing machine.
3.3 IMPACT PROPERTIES
3.3.1 INTRODUCTION:
The impact properties of the polymeric materials are directly related to the overall toughness
of the materials. Toughness is defined as the ability of the polymer to absorbed applied energy.
The area under the stress-strain curve is directly proportional to the toughness of a material. The
higher the impact strength of a material, the higher the toughness and vice versa. Impact
resistance is the ability of material to resist breaking under a shock loading ‘or’ the ability to
resist the fracture under stress applied at high speed. Impact properties of the polymers are often
modified simply by an impact modifier such as butadiene rubber or certain acrylic polymers.
3.3.2 DEFINITION
3.3.2 (a) IMPACT TEST:
Impact test is a method of determining the behavior of material subjected to
shock loading in bending or tension. The quantity usually measured is the energy absorbed
in fracturing in a single blow.
3.3.2. (b) IMPACT STRENGTH:
Energy required fracturing a specimen subjected to shock loading.
Unit : J/m
3.3.3 SIGNIFICANCE:
(1)
The excess energy pendulum impact test indicates the energy to break std. Test
specimen of specified size under stipulated conditions of specimen mounting, notching and
pendulum velocity at impact.
(2) The energy lost by the pendulum during the breakage of the specimen is the sum of
energy required,
(i) To initiate fracture of the specimen
(ii) To propagate the fracture across the specimen
(iii) To through the free end of the broken specimen
(iv) To bend the specimen
(v) To produced vibration in the pendulum arm
(vi) To produced vibration ‘or’ horizontal movement of the machine frame ‘or’
base
(vii) To overcome friction in the pendulum bearing and in the excess energy
indicating mechanism and to overcome pendulum air drag (wind age).
(viii) To indent ‘or’ deformed plastically the specimen at the line of impact.
3.3.4 TEST METHOD:
Test Method for Impact Resistance of Plastics & Electrical Insulating Material
(ASTM D 256 A & B), ASTMD1822, JISK-7111 &7112
The impact test methods are as following:
(1) Pendulum impact tests
(i) Izod impact test
(ii) Charpy impact test
(iii) Chip impact test
(iv) Tensile impact test
(2) High-rate tension test
(3) Falling weight impact test
(a) Drop weight (top) impact test
(4) Instrumented impact tests
(5) High- rate impact testers.
(a) High speed ball impact tester
(b) High speed plunger impact tester
(6) Miscellaneous impact test.
3.3.4(a) CONDITIONING:
Condition on the test specimens at 23 ± 2°C and 50 ± 5% relative humidity for not less
than 40h. prior to test in accordance with procedure ‘A’ of method D 618 for those test,
where conditioning is required. In case of disagreement, the tolerances shall be ± 1°C and
± 2% relative humidity.
3.3.4(b) Test conditions:
Conduct the test in the standard laboratory atmosphere of 23 ± 2°C and 50 ± 5% relative
humidity, unless otherwise specified test method. In case of disagreement the tolerance
shall be ± 1°C and ± 2% Relative humidity.
3.3.5 TEST SPECIMENS
3.3.6 EQUIPMENT DETAILS:
(1) The machine shall consist of a massive base on which are mentioned appear of support
for holding the specimen and which is connected, through a rigid frame and antifriction
bearing, one of a number of pendulum types hammers having an initial energy suitable for
use with the particular specimen to be tested.
(2) The pendulum shall consist of single or multi member arm with a bearing on one end
and a head containing the stick nose.
(3) The striking of the pendulum is made of hard steel, tapered to have an included angle
of 45 ± 2°C and is rounded to a radius of 3.17 ± 0.12 mm
(4) The position of the pendulum holding and releasing mechanism is such that the vertical
height of fall of the striking nose is 610 ± 2mm. This will produced a velocity of striking
nose at the movement of impact of approximately 3.46 m/sec.
(5) The effective length of pendulum is between 0.325 & 0.406m so that the aboverequired elevation of the stick nose is obtained by a raising the pendulum to an angle
between 60 and 30° above the horizontal.
(6) The machine is provided with a basic pendulum capable of delivering energy of 2.71±
0.135 J.
(7) The test specimen is supported against to rigid envil in such a position that its center of
gravity and the center of notch shall lie on the tangent to the arc of travel of the center of
percussion of the pendulum drawn at the position of the impact.
(8) Means shall be provided for determining energy remaining in the pendulum after the
breaking specimen, usually this will consist a pointer and a dial mechanism which indicate
the height of rise of the pendulum beyond the point of impact, in terms of energy remove
from the specific pendulum.
(9) The vise-pendulum and frame shall be rigid to assure correct alignment of the hammer
and the specimen, both at the movement of impact and during the propagation and to
minimize the energy loss due to vibration.
(10) A check of calibration of an impact machine is difficult to make under dynamic
condition. The basic parameters are normally checked under static condition. If the machine
passes the static test then it is assumed to be accurate.
Tensile impact tester
Pendulum impact tester
Instrument impact tester
3.3.7 PROCEDURE:
(1) Estimating the breaking energy for the specimen and select the pendulum of suitable
energy.
(2) Before testing the specimen, perform the following operation on the machine.
(a) With the excess energy indicating pointer in its normal starting portion but without a
specimen in the vise release the pendulum from its normal starting position and note
the position the pointer attains after the swings as one reading of factor ‘A’.
(b) Without resetting a pointer, raise the pendulum & release again.
(c) Repeat the above two operations several time, and calculate the record the average
‘A’ & ‘B’ readings.
(3) Check the specimen for conformity.
(4) Position the specimen precisely and rigidly but not the lightly clamped in the vise.
(5) Calculate the machine correction for indicating breaking strength of the specimen and
factor ‘A’ & ‘B’ using table ‘or’ the graph-describing appendix X2.
(6) Calculate the average impact strength of the group of the specimen.
3.3.7(a) IZOD TEST:
 The test specimen is clamped into position so that the notched end of the specimen is
facing the striking edge of the pendulum.
 Check for properly positioned the test specimen.
 The pendulum hammer is released, allowed to strike the specimen and swing through.
 If the specimen does not break, more weights are attached to hammer and the test is
repeated until failure is observed.
 The impacts values are read directly in in- lbs are ft- lbs from the scale.
Diagram illustrating izod impact test specimen properly positioned in test fixture
3.3.7(b) CHARPY IMPACT TEST:
 This test is conducted in a very similar manner to the Izod impact test.
 The only difference is the positioning of the specimen.
 In this test the specimen is mounted horizontally and supported at both ends. Only the
specimens that break completely are considered acceptable.
 The charpy impact strength is calculated by dividing the indicator reading by the
thickness of the specimen.
 The results are reported in ft-lbs/in. of notch for notched specimen and ft-lbs /in. for
unnotched specimens.
Charpy test set-up
3.3.7(c) Falling-Weight Impact Test:
 The falling impact test, also known as the drop impact test or the variable-height impact
test, employs a falling weight.
 This falling weight is a tup with a conical nose, a ball, or a ball-end dart.
 The energy required to fail the specimen is measured by dropping a known weight from a
known height onto a test specimen.
 This test is also very suitable for determining the impact resistance of plastic films, sheets
and laminated materials.
Three basic ASTM tests are commonly used depending upon the application:
ASTMD 3029
Impact resistance of rigid plastics sheeting
ASTMD 1709
Impact resistance of poly ethylene film by the free falling dart method
ASTMD 244
Test for impact resistance of thermoplastics pipe and fittings by
means of a tup.
Falling dart impact tester
3.3.7(d) DROP IMPACT TEST:
 The test is carried out by raising the weight to a desired height manually or automatically
with the use of motor-driven mechanism & allowing it to fall freely on to the others side of
the round- nosed punch.
 The punch transfers the impact energy to the flat test specimen, which is positioned, on a
cylindrical die or a part lying on the base of the machine.
 The kinetic energy is possessed by the falling weight at the instant of impact is equal to
the energy used to raise to the height of drop and is the potential energy possessed by the
weight as it is released.
 Since the potential energy is expressed as the product of weight and height, the guide tube
is marked with a linear scale representing the impact range of the instrument in in-lb.
 Thus, the toughness or the impact strength of a specimen or a part is read directly off the
calibrated scale in in-lb.
 The energy loss due to the friction in the tube or due to the momentary acceleration of the
punch is negligible
Drop impact tester
Impact tester specifically designed for impact testing pipe & fitting
3.3.9 FORMULA AND CALCULATIONS:
Energy required breaking the sample (J)
Impact strength (J/m) =
(Izod / Charpy)
Thickness (m)
Dart Impact Test:
Calculate Wf = WL - [ ΔW (S/100 – ½)]
Where,
Wf = impact failure weight, gms,
ΔW = uniform weight increment used, gms,
WL = lowest missile weight, gms, according to the particular ΔW used, at
which 100% failure occurred and
S
= sum of the percentages of breaks at each missile weight (from a weight
corresponding to no failures upto and including WL )
3.3.10 FACTORS INFLUENCING:
•Processing Parameters
•Rate of Loading
•Crystallinity and Molecular Weight
• Preparation of Test Specimen
•Temperature of testing
•Radius of Notchg.
•Angle of Notch
3.3.11 RESULTS:
The result is including following.
(1) Complete identification of the material tested, including type source, and previous
history.
(2) A statement of how the specimen work prepared the testing condition used.
(3) The capacity of the pendulum in joules.
(4) The nominal width of the specimen.
(5) Should specify clearly Izod / Charpy method.
(6) Should report test results with notch or un-notch along with test method.
3.3.13 SAFETY PRECAUTIONS:
1) The specimen should be conditioned as per the test method..
2)
The test specimen should be impacted within 10 seconds after removing from
conditioning chamber.
3) The sample should be striked on at least four different places on center.
4) The mass of weight and its height of fall should be carefully calculated.
5) The mass should be 25mm hemispherical striking end.
6) Notch dimensions should be maintained precisely in samples.
3.3.14 REFERENCE: ASTM STD.
D 618 Methods of conditioning plastics and electrical insulating materials and
testing
D 647 practical. For design of mold for test specimen of plastic molding mater.
3.4 COMPRESSIVE PROPERTIES
3.4.1 INTRODUCTION:
Compressive properties describe the behaviour of a material when it is subjected to a
compressive load at a relatively low and uniform rate of loading.
Compressive properties include modulus of elasticity; yield stress, deformation
beyond yield point, compressive strength, compressive strain and slenderness
ratio.
3.4.2 DEFINITIONS:
3.4.2 (a) COMPRESSIVE STRENGTH: The maximum load sustained by a test
specimen in a compressive test divide by the original cross section area of the
specimen.
3.4.2 (b) COMPRESSIVE DEFORMATION: - The decrease in length produced in the gauge
length of the test specimen by a compressive load. It is expressed in unit of length.
3.4.2 (c) COMPRESSIVE STRAIN: - The ratio of compressive deformation to the gauge
length of the test specimen, i.e., the change in length per unit of original length along the
longitudinal axis. It is expressed as dimension ratio.
3.4.2 (d) SLENDERNESS RATIO:- The ratio of the length of a column of uniform cross
section to its least radius of gyration known as slenderness ratio.
3.4.2 (e) MODULUS OF ELASTICITY:- The ratio of stress to corresponding strain below
the proportional limit of a material. It is expressed as force per unit area, based on the
average initial cross- sectional area.
3.4.2 (f) COMPRESSIVE YIELD POINT:- The fist point of stress-strain diagram at which an
increase in strain occurs without an increase in stress.
Unit :- kg/cm2
3.4.3 SIGNIFICANCE:
1) Compressive test provides information about compressive properties of plastics when
employed under conditions approximating these under which the tests are made.
2) Compressive properties include the modulus of elasticity, yield stress; deformation
beyond yield point at the compressive strength, material processing a low order of ductility
may not exhibit yield point.
3) Compression tests provide a standard method of obtaining data for research and
development, quality control, acceptance or rejection under specifications and special
purposes.
3.4.4 TEST METHOD:
Test Method for Compressive Properties of Rigid Plastics (ASTM D 695), ISO 75-1
and 75-2
3.4.5 TEST SPECIMEN
3.4.5 (a) Specimen preparation method: For rod materials, the test specimen shall have a diameter equal to diameter of tube and a
length of 25mm. For crushing load determination, the specimen size is the same, with
the diameter becoming the height. Specimens are prepared by machining or moulding.
3.4.5 (b) Dimensions of test specimen:
3.4.6 EQUIPMENTS DETAILS:
1) Universal Testing machine
2) Drive mechanism
3) Load indicator
4) Compressometer or deflectometer – To measure any change in distance between two
fixed points on the test specimen at any time during the test.
5) Compression tool
6) Supporting jig
7) Micrometers.
A typical test set-up for compression testing
3.4.7 TEST PROCEDURE:
1) Measure the width and thickness of the specimen to the nearest 0.01 mm at several points
along its length.
2) Calculate and record the minimum value of the cross-sectional area.
3) Measure the length of specimen and record the value.
4) Place the test specimen between the surfaces of the compression tool, taking care to align
the center of its long axis with the centerline of the plunger and to ensure that the ends of
the specimen are parallel with the surfaces to the compression tool.
5) Place thin specimens in the jig so that they are flush with the base and centered.
6) If only compressive strength, then set the speed control at 1.0 mm / min and start the
machine.
7) If strain- stress data are desired then,
a) Attach compressor
b) Record load and corresponding compressive strength at appropriate intervals of
strain.
c) After the yield point reach, it is desirable to increase the speed from 5 to 6
mm/min. and allow machine to run at this speed until the specimen breaks.
3.4.9 FORMULA E AND CALCULATION
(1) Compressive strength: Calculate the compressive strength by dividing the max.
Compressive load carried by the specimen during the test by the original minimum
cross sectional area of the specimens. Express the result in Mpa.
Load (kg)
(1)
Compressive strength =
Original cross sectional area (cm2)
Maximum load recorded (N)
(2) Compressive strength at yield (N/mm²) =
Cross-section area (mm²)
Load recorded at break (N)
(3) Compressive strength at break (N/mm²) =
Cross-section area (mm²)
Difference in stress
(4) Compressive Modulus =
Difference in corresponding strain
Change in length (Deformation)
(5) Deformation at yield, Strain (ε) =
Original length (gauge length)
(6) Percent Deformation = ε x 100
If the specimen gives a yield load that is larger than the load at break, calculate “percent
Deformation at yield” otherwise; calculate “percent Deformation at break”.
3.4.10 FACTORS INFLUENCING:
a. Temperature and Humidity
b. Method of specimen Preparation
c. Effect of Plasticizer and filler
d. Molecular Weight and Molecular Weight Distribution
e. Crystallinity
f.
Rate of Straining
3.4.11 TEST RESULTS
The results shall include the following1) Speed of testing.
2) Compressive strength average value and standard deviation.
3) Type of test specimens and dimensions.
4) Compressive yield strength and offset yield and standard deviation.
5) Modulus of elasticity in compression (if required)
3.4.13 SAFETY PRECAUTIONS:
1. Specimen should be placed in the centre between to fixtures.
2. Observation should read carefully.
3. Before test, test specimen should be checked properly for any moulding or machining
defects.
4. The specimens should be tested within 10 seconds after removing from conditioning
chamber.
3.4.14 REFERENCES: ASTM STANDARDS
# D618 Method of conditioning plastics and electrical insulating materials for testing.
# D638 Test method for tensile properties of plastics.
# D695 Test method for compressive properties of rigid plastics.
# D3410 Test method for compressive properties of unidirectional crossply fiber resin
composites.
# E4 practice for load verification of testing machine.
3.5 SHEAR STRENGTH
3.5.1 INTRODUCTION
Shear strength of plastic material is defined as the ability to withstand the maximum
load required to shear the specimen so that the moving portion completely clears the
stationary portion. Forcing a standardized punch at a specified rate through a sheet of
plastics until the two portions of the specimen completely separate carries out shear
strength test.
3.5.2 DEFINITION:
3.5.2(a) SHEAR STRENGTH: The maximum load required to shear a specimen in such a
manner that the resulting pieces are completely clear of each other.
Unit is lb / inch².
3.5.3 SIGNIFICANCE:
Shear strength data is of great importance to a designer of film and sheet products
that tends to be subjected to such shear loads. Most large molded and extruded products
are usually not subjected to shear loads.
3.5.4 TEST METHOD:
Test Method for shear strength of plastics by punch tool (ASTM D 732)
3.5.5 TEST SPECIMEN
3.5.5(a) Sample preparation method and Dimensions of Test specimen:
The specimen shall consists of a 50mm (2inch) square or a 50mm (2inch) dia disk
cut from sheet material or moulded into this form. The thickness of the specimen is from
0.127 to12.7mm (0.005 to 0.500inch). The upper and lower surface is parallel to each
other and reasonably 11mm (7/16inch) in diameter is drilled through the specimen at its
centre.
3.5.5 (a). 1 CONDITIONING:
Condition the test specimen at 23ºC and 50% relative humidity for not less then
40h prior
to test in accordance with procedure A of methods D618, for those tests where conditioning
is required. In case of disagreement, the tolerance shall be 1ºC(1.8F) and 2% relative
humidity.
3.5.5 (a). 2 TEST CONDITIONS:
Conduct test in the standard laboratory atmosphere of 23 + 2°C and 50 + 5% relative
humidity, unless otherwise specified in the tests methods. In cases of disagreement, the
tolerances shall be + 1°C and
+ 2% relative humidity.
3.5.6 EQUIPMENT DETAILS
3.5.6(a) Testing machine:
 Any suitable testing machine of the constant rate of crosshead movement type. The
testing machine is equipped with the necessary drive mechanism for importing to the
crosshead a uniform, controlled velocity with respect to the base.
 The testing machine shall also be equipped with a load indicating mechanism capable of
showing the total compressive load carried by the test specimen. This mechanism is
essentially free from inertia – lag at the specified rate of testing and shall indicate the load
with an accuracy of + 1% of the indicated value or better.
Shear strength test set up
3.5.6(b) Shear Tool:
A shear tool of the punch type, which is so, constructed that the specimen is
rigidly clamped both to the stationary block and movable block so that it cannot be
deflected during the test.
3.5.6(c) Micrometers
Suitable micrometers for measuring the testing thickness of the test specimen
to an incremental discrimination of at least 0.025 mm are used.
3.5.7 TEST PROCEDURE:
• Measure the thickness of the test specimen with a suitable micrometer to the nearest
0.025 mm at several points 12.7 mm from its centre.
• Place the specimen over the 9.5 mm pin of the punch and fasten tightly to it by means of
the washer and nut.
• Assemble the tool jig and tighten to bolts.
• Maintain the crosshead speed of the machine during tests at 1.25 mm/ min measured
when the machine is running idle. The tolerance is 1.3 + 0.3 mm/min.
• Pushdown the punch for enough so that the shoulder clears the specimen proper.
• The specimen will then be adjacent to the necked-down portion of the punch and it is
possible to remove the specimen readily from the tool.
3.5.9 FORMULA:
Shear strength is calculated as follows:
Force required to shear the specimen
Shear strength (psi) =
Area of sheared edge
Area of sheared edge = (circumference of punch) x (thickness of specimen)
Calculate shear strength in Mpa determined by dividing the load required to shear the
specimen by the area of the sheared edge, which shall be taken as the product of the thickness
of the specimen by the circumference of the punch.
3.5.10 FACTORS INFLUENCING
• Temperature and Humidity
• Method of specimen Preparation
• Effect of Plasticizer and filler
• Molecular Weight and Molecular Weight Distribution
• Crystallinity
3.5.11 TEST RESULTS:
The result shall include the following:
1. Complete identification of the material tested including type, source, manufacturers
code no, firm, principle dimensions, previous history etc.
2. Method of tests type of tests, specimen & dimensions.
3. Atmospheric conditions in the test room.
4. Conditioning procedure used.
5. Diameter of punch.
6. Load in Newton’s required to shear each specimen and average value.
7. Shear strength in the Mpa for each specimen, the average value and the standard
deviation.
3.5.12 SAFETY PRECAUTIONS:
1. Specimen is free from notch, voids or any specimen preparation defects.
2. The hole is in centre and diameter of hole and specimen is correct
3. Specimen is clamp properly.
4.
Alignments of shear tool (Clamp and punch) are proper and not touch the wall of
clamp to punch.
5. Conditioning and test temp should be correct
6. Don’t touch the shear printer when punch comes down or test performs.
7. Do not touch the specimen or movable part of tool during testing.
8. Specimen should be free from voids and grease, oil.
3.5.13 REFERENCES: ASTM Standards:
D618 methods of conditioning plastics and electrical insulting materials for testing
D4066 specification for Nylon Injection and extrusion materials
E4 methods of load verification of testing materials
E691 practice for conducting an inter-laboratory test programme to determine the
precision of Test methods.
3.6(A) TEAR STRENGTH - INTIATION
3.6(A). 1 INTRODUCTION
This test method covers the determination of the tear resistance of flexible plastic film
and sheeting at very low rates of loading.
3.6(A). 2 DEFINITIONS:
The test method covers the determination of the average force to propagate tearing to a
specified length of plastic film or non-rigid sheeting. After the tear has been started using
an element of types tearing tester to specimen are cited a rectangular type and one with a
constant radius testing length. The latter shall be preferred are free specimen.
3.6(A). 3 SIGNIFICANCE:
This test method is of value in ranking the tearing resistance of plastic films and
thin sheeting of comparable thickness. Variable elongation and oblique tearing effects on
the more extensible films preclude its use as a precise production tool for this type of
plastic. This test method is used for specification acceptance testing method.
3.6 (A). 4 TEST METHOD:
Test Method for Initial Tear Resistance of Plastic Film & Sheeting. ASTM D 1004
3.6 (A). 5 TEST SPECIMENS:
Test specimen is cut to form a constant radius testing length. That is the preferred
or reference specimen type, since its geometry automatically compensates for the problem of
oblique tearing. The dimensions are 101.60 mm x 19.05mm and 0.750” rad.
3.6 (A). 5 .1 CONDITIONING:
Condition the test specimens at 23  2C (73.43.6F ) and 50  5%
relative humidity for not less than 40h prior to test in accordance with procedure A of
method D 618 for these tests where conditioning is required. In cases of disagreement the
tolerances shall be 1C (1F) and 2% relative humidity.
3.6 (A). 6 EQUIPMENT / INSTRUMENTS DETAILS:
Pendulum impulse type testing apparatus consisting of the following:
1) Testing machine
2) Grips
3) Thickness measuring devices
4) Die
3.6(A). 7 TEST PROCEDURES:
 Measure and record the thickness of each specimen at several points to the
accuracy limits of the measuring devices and the average thickness.
 Place the specimen in the grips of the testing machine so that the long axis of the
enlarged ends of the specimen is in line with the points of attachment of the grips to the
machine.
 Apply the load at 51 mm/ min. rate of grip separation. After complete rupture of
the specimen, the maximum tearing load is noted from the dial scale or recorder chart
and recorded.
3.6(A).9FORMULA:
1. Calculate the average resistance to tearing from all specimens tested in each principal
direction of orientation. The tearing resistance is denoted as gf or pounds.
16 * 9.81* average scale reading
Average tearing force, mN =
n
16 * average scale reading
Average tearing force, gf =
n
Where
n =1
16 * 9.81* average scale reading * gf capacity
Average tearing force, mN =
n * 1600 gf
16 * average scale reading * gf capacity
Average tearing force, gf =
n * 1600 gf
Where n = 1 as number of piles if used
16 * average scale reading * capacity N
Average tearing force, mN =
n * 15.7 N
16 * average scale reading * capacity N
Average tearing force, gf =
9.81 * n * 15.7 N
Where n =1 as number of piles if used
average scale reading
Average tearing force, mN =
n
average scale reading
Average tearing force, gf =
9.81 * n
Where n =1 as number of piles if used.
average scale reading * 9.81
Average tearing force, mN =
n
average scale reading
Average tearing force, mN =
n
2. Calculate standard deviation (Estimated),
Σ (X² - nX²)
S=
(n-1)
Where,
S = estimated standard deviation
X = value of a single observation
n = number of observations
X = arithmetic mean of the set of observations
3.6(A).10FACTORS INFLUENCING:
a. Temperature and Humidity
b. Test Speed
c. Method of specimen Preparation
d. Effect of Plasticizer and filler
e. Molecular Weight and Molecular Weight Distribution
f.
Crystallinity
g. Rate of Straining
3.6 (A). 11 TEST RESULTS:
The report shall include the following
1. Average thickness of each test specimen and average thickness of all test specimens.
2. Type of testing machine used
3. Number of specimens tested in each principal direction
4. Average value of tear strength
5. Standard deviation from the averaged values obtained for specimens tested in each
principal direction.
3.6 (A). 12 SAFETY PRECAUTION:1.
2.
3.
4.
5.
Selection of scales should be more-than 15% of approx test value
Specimen should be proper in shape & size.
Notch should be straight and middle in the specimen
Don’t touch the knife when specimen notch
Don’t touch pendulum when test perform (close the chamber of machine)
3.6 (A). 13 REFERENCES: ASTM Standards:
D 374 test methods for thickness of solid electrical insulation.
D 618 practice for conditioning of plastics
D 882 test methods for tensile properties of thin plastic sheeting
3.6 (B) TEAR STRENGTH - PROPAGATION
3.6 (B). 1 INTRODUCTION
This test method covers the determination of the average force to
propagate tearing to a specified length of plastic film or non-rigid sheeting. After the tears
start using an element of types tearing tester to specimen is cited a rectangular type and one
with a constant radius testing length. The latter is preferred are free specimen.
3.6 (B). 2 SIGNIFICANCE:
This test method is of value in ranking relative tearing resistance of
various plastic films and thin sheeting of comparable thickness. Experience has shown the
test to have it best reliability, on relatively less extensible films and sheeting.
Variable elongation and oblique tearing effects on the more extensible
films preclude its use as a precise production tool for this type of plastic. This test method is
used for specification acceptance testing method.
3. 6 (B). 3 TEST METHOD:
Test Method for Propagation Tear resistance of Plastic Film & Thin sheeting by a
Pendulum Method. - ASTM D 1922, ISO 6383 / 2
3. 6 (B). 4 TEST SPECIMEN:
Test specimen is cut to form a constant radius testing length. That is the preferred
or referee specimen type, since its geometry automatically compensates for the problem of
oblique tearing. Specimens are cut to form a rectangle 76 mm or more in width by 63 mm
in length and plainly marked to denote intended direction to tear.
3. 6 (B). 5 EQUIPMENT / INSTRUMENTS DETAILS:
Pendulum impulse type testing apparatus consisting of the following:
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
Stationary clamp
Movable clamp
Stop watch
Indicating device
Capacity instruments
Template, die or shear type
Razor blades
Thickness measuring device
3. 6 (B). 6 TEST PROCEDURE:
 At least ten specimens in each of the principal film or sheeting directions are tested.
 Measure and record the thickness of each specimen as the average of three readings
across its center in the direction in which it is to be torn.
 Read the thickness to a precision of 0.0025mm (0.0001 in.) or better except for
sheeting greater than 0.25mm (10 mils) thickness, which is read to a precision of
0.025mm (0.001in.) or better.
 Keep the pendulum in its raised position, place the specimen midway in the clamps
so that its upper edge is parallel to the top of the clamps and the initial slit is at the
bottom of and between the clamps at right angles to their top.
 Slit the firmly clamped specimen with the sharp spring-loaded knife if it is not slit
during cutting.
 Lay the upper testing portion of the specimen over in the direction of the pendulum
pivot.
 Release the sector stop and tear the specimen.
 The sector completes its return swing; catch it with thumb and forefinger of the left
hand, being careful not to disturb the position of the pointer.
 Check the specimen. If it tore through the constant radius section within an
approximate angle of 60° on either side of the vertical line of intended tear, record the
pointer reading to the nearest 0.5 units.
 Reject if the line of tear is 60° from the vertical.
 Reject all specimens that tear obliquely more than 9.5 mm from the vertical line of
intended tear, if rectangular specimens.
3. 6 (B). 8FORMULA:
1. Calculate the average tearing force, if the standard 1600 – gf instrument with a 0 to
100 scale is used
16 x 9.81 x average scale reading
Average tearing force, mN =
n
Where n =1
16 x average scale reading
Average tearing force, gf =
n
Where n = 1, or number of piles, if used
2.Calculate the average tearing force, if an instrument has direct reading scale in
millinewtons,
9.81 x average scale reading
Average tearing force, mN =
n
Where, n =1
Average scale reading
Average tearing force, gf =
n
Where n = 1, or number of piles, if used
3. 6 (B). 9 FACTORS INFLUENCING:
a. Temperature and Humidity.
b. Test Speed
c. Method of specimen Preparation
d. Effect of Plasticizer and filler
e. Molecular Weight and Molecular Weight Distribution
f.
Crystallinity
g. Rate of Straining
3. 6 (B). 10 TEST RESULTS:
The report shall include the following
(1) Type and direction of specimens tested:
Rectangular or constant radius, parallel or normal to the machine direction of the
film.
(2)
Capacity of the tester.
3. 6 (B). 11 SAFETY PRECAUTION:1. Selection of scales should be more-than 15% of approx test value
2. Specimen should be proper in shape & size.
3. Notch should be straight and middle in the specimen
4. Don’t touch the knife when specimen notch
5.
Don’t touch pendulum when test perform (close the chamber of machine)
3. 6 (B). 12 REFERENCES: ASTM Standards:
D 374 test methods for thickness of solid electrical insulation.
4.1 CREEP PROPERTIES
4.1 .1 INTRODUCTION:
Today plastics are used in application that demand high performance and extreme
reliability. Many components, conventionally made in metals are now made in plastics. An
increasing number of designer have now recognized the importance of thoroughly
understanding the behaviour of plastic under long term load and varying temperatures and
such behaviour is described in terms of creep properties.
4.1. 2 DEFINITION:
4.1.2 (a) Creep - When a plastic material is subjected to a constant load, it deforms
quickly to a strain roughly predicted by its stress-strain modulus, and then continues to
deform slowly with time indefinitely or until rupture or yielding causes failure. This
phenomenon under load with time is called creep
4.1.2 (b) Creep modulus (Apparent modulus):
It is defined as the ratio of initial stress to creep strain.
4.1.2 (c) Creep rupture strength:
Stress required to cause fracture in a creep test within a specified time.
Unit:- Flexural Creep = lb/inch2
4.1.3 SIGNIFICANCE: (i)
Data from creep and creep rupture tests are necessary to predict the creep
modulus and strength of material under long-term loads and to predict dimensional
changes that occurs as a result at such loads.
(ii)
Data from these tests methods are used to compare material in that design at
fabricated parts to characterized plastic for long term performance under constant load
and under certain condition for specification purpose.
4.1.4 TEST METHODS:
Test Method for Tensile, Compressive and Flexural creep and Creep Rupture of
plastics (ASTM D 2990), JIS-7115
The test method consist of measuring the extension or compression was a
function of time and time to rupture of failure of a specimen subject to a constant tensile
or compressive load under specification environmental conditions.
4.1.5 TEST SPECIMEN:
4.1.5 (a) SAMPLE PREPARATION METHODS:
(i)
The test specimen for tensile creep measurement is either type1 or type 2 as
specified in test method D 638
(ii) Specimen for unconfined compressive creep test is suitably prepared in the manner
described in test method D 695, except that the length is increased so that the
slenderness ratio lies between 11 and 15.
(iii) Test specimen is made by injection or compression moulding or machining from
sheets or other fabricated form.
(iv) Specimen prepare from sheets are cut in the same direction.
4.1.5 (b) DIMENSIONS OF TEST SPECIMEN
(i)
Test specimen for the compressive creep measurements using the guide tube is
slender walls of square cross section with side measuring 4.850 ± 0.025 mm and
diagonal 6.860± 0.025 mm.
(ii) Test specimen for flexible creep is a rectangular bar conforming to the requirements
of section 5 at test method D-790.
The width and thickness of the specimen is measured at room temperature
which is suitable in creep testing at a single temperature at each stress is two if four or
more levels of stress are used or three if lower than four micrometer.
Mould dimension of types S and L tensile impact specimen
4.1.5 (c ) CONDITIONING:
(i) Condition the test specimen at 23 ± 2°C and 50 ± 5% relative humidity for not less than
40 h prior to test in accordance with procedure A of test methods D 618 for those tests
where conditioning is required.
(ii) The specimen shell be preconditioning in the test environment for at least 40 h prior to
being tested.
4.1.6 EQUIPMENT DETAILS:
(i) Tensile Creep: Grips-The grips and gripping techniques are minimizing eccentric
loading of the specimen. It is recommend that grips permit the final Centring of the
specimen prior to applying the load.
(ii) Flexural creep:
1. Test rack
2. Stripping
3. Loading system
4. Extension, compression and deflection measurement device
5. Time measurement device
6. Temperature control and measurement device
7. Vibration control device.
4.1.7 TEST PROCEDURE:
4.1.7 (a) Tensile Creep:
(i) Mount a properly conditioned and measured specimen in the grips, tensile creep
fixture.
(ii) Attach the deformation-measuring device to the specimen.
(iii ) Apply the constant load to a tensile test specimen and smoothly to the specimen
and measuring its extension as a function of time.
(iv) The extension measurement is carried out by taking two gauge marks on the tensile
specimen and measure the distance between the marks at specified interval time.
(v) Measure temperature, relative humidity and other environmental variables and
deformation of control specimen with the some schedule as that for deformation of the
test specimen.
4.1.7(b) Flexural Creep
(i)
Flexural creep measurements are also made by applying a constant load to the
standard flexural test specimen and measuring its deflection as a function of time.
(ii)
The deflection of the specimen at mid-span is measured using a dial indicator
gauge.
(iii)
The electrical resistance gauges may also be used in place of a dial indicator.
(iv)
The deflections of the specimen are measured at a predetermined time interval.
Flexural creep testing
4.1.9 FORMULA AND CALCULATION:
(i) For flexural measurements calculate the maximum fibre stress for each specimen in Mpa
as follows:
3PL
S=
2bd2
Where
S = Stress, N/mm² (Mpa)
P = Load, N (lbf)
L = Span, mm (in)
b = Width, mm (in) and
d = depth, mm (in)
(ii)
Calculate the percent flexural creep strain,
6Dd
r=
x 100
L2
r = maximum percent creep strain, mm /mm (in/in)
D = maximum deflection at mid-span, mm (in)
d = depth, mm (in) and
L = span, mm (in)
Initial applied stress
(iii) Creep (Apparent) modulus at time t =
Creep strain
4.1.10 FACTORS INFLUENCING:
a. Temperature of testing -The creep Resistance is inversely proportional to the
Temperature.
b. Humidity of Environment – The creep Resistance is inversely proportional to the
Humidity level in moisture sensitive material
c. Effect of Reinforcing Filler - Creep Resistance is directly proportional to the loading of
Reinforcing Filler.
d. Effect of Plasticizer - Creep Resistance is inversely proportional to Plasticizer.
e. Aromatic Content & Cross-linking of Polymer - Creep Resistance is directly
proportional to the Aromatic Content & Cross-linking of Polymer.
Case - 4 Stress-Time curve
Case – 5 Creep and Stress relaxation
4.1.11 TEST RESULTS:
The report shall include the following:
(i)
For each test temperature plot log creep strain in percent versus long time in
hours under load with stress as a parameter
(ii) Where deformation measurements at load specimen have been corrected from
unload control specimen.
(iii) When a material soul significance dimension change due to environmental
alone, any properties calculated from the creep data is levelled corrected or
uncorrected, depending on which approach is used
4.1.12 SAFETY PRECAUTIONS:
1.
Specimen is free from any preparation defects like burrs, notch
etc.
2.
Specimen gauge mark is clear and permanent.
3.
Measurement of initial position of mark is clear.
4.
Temperature is maintained.
4.1.13 REFERENCES: - ASTM standards
D618 Method of conditioning plastic and electrical insulating materials
for testing.
D790 Test methods for flexural properties of unreinforced and
reinforced plastic and electrical insulating material
D638 Test method for tensile properties of plastics.
4.2 STRESS RELAXATION
4.2. 1 Introduction:Stress relaxation, characteristic behavior of the polymer is studied by applying a fixed
amount of deformation to a specimen and measuring the load required to maintain it as a
function of time. This phenomenon of creep and stress relaxation is further clarified
schematically in figure below.
Creep and Stress relaxation
4.2.2 DEFINITION:- Stress relaxation is defined as a gradual decrease in stress with
time, under a constant deformation (strain).
Stress Relaxation:- The gradual decrease in stress with time under a constant
deformation (Strain).
Stress optical sensitivity:- the ability of some material to exhibit double refraction of
light when placed under stress is referred to as stress-optical sensitivity.
Stress Concentration :- The magnification of the level of applied stress in the region of
a notch, crack, void, inclusion, or other stress rises.
Stress:- The ratio of applied load to the original cross sectional area expressed in pounds
per square inch.
4.2. 3 SIGNIFICANCE:
Stress relaxation behavior of the polymers is overlooked
by many design engineers and researchers, partly because the creep data is much easier
to obtain and is readily available. However, many practical applications dictate the use of
stress relaxation data. For example, extremely low stress relaxation is desired in the case
of threaded bottle closure, which may under constant strain for a long period.
Stress-Time curve
4.2.4. TEST METHOD
Practice for Testing Stress – Relaxation of Plastics (ASTM D 2991)
Stress relaxations measurements can be carried out using a tensile testing
machine such as that describe earlier. However, the use of such a machine is not always
practical because the stress relation test ties up the machine for a long period of time. The
equipment for a stress relation test must be capable of measuring very small elongation
accurately, ever when applied high speeds. Many sophisticated pieces of equipment now
employ a strain gauge or a diff. Transformer along with a chart recorder capable of plotting
stress as a function of time. At the beginning of the experiment the strain is applied to the
specimen at a constant rate to achieve the desired elongation. Once the specimen reaches
the desired elongation the strain is held constant for predetermined amount of time, the
stress delay, which occurs due to stress relaxation, is observed as function of time. If a chart
recorder is not available the stress value at diff. Time intervals are recorded and the result
are plotted to obtain a stress versus time curve.
4.2. 5 TEST SPECIMEN
4.2. 5 (a) SAMPLE PREPARATION METHODS:
a)
Test specimen is made by injection or compression moulding or machining from
sheets or other fabricated form.
b) Specimen prepares from sheet is cut in the same direction.
c) The width and thickness of the specimen is measured at room temperature which is
suitable in Stress relaxation testing at a single temperature at each stress is two or four or
more levels of stress are used or three if lower than four micrometer.
4.2.5 (b) CONDITIONING:
(i) Condition the test specimen at 23 ± 2°C and 50 ± 5% relative humidity for not less
than 40 h prior to test in accordance with procedure A of test methods D 618 for those
tests where conditioning is required.
(ii) The specimen shell be preconditioning in the test environment for at least 40 h prior
to being tested.
4.2. 6 EQUIPMENTS DETAILS:
1. Test rack
2. Stripping
3. Loading system
4. Extension, compression and deflection measurement device
5. Time measurement device
6. Temperature control and measurement device
7. Vibration control device.
4.2. 7 TEST PROCEDURE:
 Stress relaxation a measurement is carried out by using a tensile testing machine such as
that describes earlier.
 The equipment for a stress relaxation test must be capable of measuring very small
elongation accurately, even when applied high speeds. Many sophisticated pieces of
equipment now employ a strain gauge or a difference.
 The strain is applied to the specimen at a constant rate to achieve the desired elongation.
 Once the specimen reaches the desired elongation, the strain is held constant for
predetermined amount of time, the stress decay, which occurs due to stress relaxation, is
observed as function of time.
 If a chart recorder is not available the stress values at different time intervals are recorded
and the results are plotted to obtain a stress versus time curve.

The stress data obtained from stress relation experiment is converted to a more
meaningful apparent modulus data by simply dividing stress at a particular time by the
applied strain.
 The curve is re-plotted to represent apparent modulus as a function of time.
 The use of logarithmic co-ordinates further simplifies the stress relaxation data by
allowing us to use standard extrapolation methods such as the one used in creep
4.2.9 FORMULA AND CALCULATION:a) For Stress relaxation measurements calculate the maximum fibre stress for each specimen
in megapascals as follows:
S = 3PL
2bd2
Where
S = Stress, mpa
P = Load, N (Ibf)
L = Span, mm (in)
B = Width, mm (in) and
D = depth, mm (in)
b) Calculate
6Dd
The max. strain r =
L2
Where
r
D
d
L
=
=
=
=
maximum strain , mm /mm (in/in)
maximum deflection at mid-span, mm(in)
depth , mm (in) and
span , mm (in)
4.2. .10 FACTORS INFLUENCING:
a) Temperature of testing
b) Humidity of Environment
c) Effect of Reinforcing Filler
d) Effect of Plasticizer
e) Aromatic Content & Cross-linking of Polymer
4.2. 11 TEST RESULTS:
The report shall include the following:
a) For each test temperature plat log creep strain in percent versus long time in
hours under load with stress as a parameter
b) Where deformation measurements at load specimen have been corrected from
unload control specimen.
c) When a material soul significance dimension change due to environmental alone,
any properties calculated from the creep data is leveled corrected or uncorrected,
depending on which approach is used
4.2.12 SAFETY PRECAUTIONS:
1. Specimen should be free from any preparation defects like burrs, notch etc.
2. Specimen gauge mark should be clear and permanent.
3. Measurement of initial position of mark should be clear.
4. Temperature should be maintained.
4.2.13 REFERENCES:
1. Handbook of plastics testing technology –VISHNU SHAH
5.1(a) ABRASION RESISTANCE FOR
TRANSPARENT PLASTICS
5. 1(a). 1 INTRODUCTION:
This test method describes a procedure for estimating the resistance of transparent
plastics to one kind of surface abrasion by measurement of its optical effects. Abrasive
damage is judged by that percentage of transmitted light, which in passing through the
abraded track, deviates from the incident beam by forward sweltering.
For the purpose of this test method, only light flux deviating more than 0.044 rad
(2.5˚) on the avg. is considered in this assessment of abrasive damage. The values stated in SI
units are to be regarded as the standard.
5. 1(a). 2 DEFINITION
Abrasion Resistance:- Abrasion Resistance is defined as the ability of a material to
withstand mechanical action (such as rubbing, scrapping or erosion) that tends
progressively to remove material from its surface.
Unit:- mg/1000 cycles
5. 1(a). 3 SIGNIFICANCE:
1. Transparent plastics material when used as enclosures are subjected to wiping and
cleaning hence the maintenance of optical quality of a material after abrasion is important.
2. Although this test method does not provide fundamental data. It is suitable for grading
materials relative to this type of abrasion in a manner that co-relates with service.
1. 1(a). 4 TEST METHOD:
Test Method for Resistance of Transparent Plastics to Surface Resistance (ASTM-D
1044, JIS-7205-77)
5. 1(a). 5 TEST SPECIMEN
The specimens are clean, transparent disks 102 mm (4-inch) in diameter
are plates 102 mm (4-inch square) having both surface substantially plane and parallel,
they are cut from sheets or molded in thickness up to 12.7 mm (1/2 inch). A 6.3 mm (1/4
inch) hole is centrally drilled in each specimen. Three such specimens are tested per
sample. Except for inter laboratories are specification test when ten specimens are tested.
5.1(a). 6 CONDITIONING:
Condition the test specimens at 23 + 2˚C and 50 ± 5% relative humidity or not
less than 40 hours prior to test in accordance with procedure A of test methods D 618 for
these tests where conditioning is required. In case of disagreement the tolerances shall be
± 1˚C and 2% relative humidity.
5. 1(a). 7 EQUIPMENT:
1. Abrader
2. Refacing stone
3. Abrasive wheels
4. Abraser turn table
5. Photometer
6. Stops
7. Specimens’ holder.
Abrasion tester
5. 1(a). 8 TEST PROCEDURE:
1. Mount the pair of “calibrate” wheels to be used on their respective flange holders. Taking
care must be handle them by the abrasive surface. Select the load to be used and affix it to the
abraser, mount a ST-11 refacing stone fine side up, on the turntable.
1.1 The use of vacuum cleaner is recommended to remove residue.
1.2
Reface new wheels for 100 cycles reface previously used wheels for 25 cycles.
1.3
Discard the ST-11 refacing stone when grooves or ridges first become evident.
2. Mount the specimen on the specimen holder and subject it to abrasion for a selected no. Of
cycles.
3. Using an integrating sphere photometer that is properly adjusted.
4. Place the specimen in the holder and measure the percentage of transmitted light that is
diffused by abraded track on at least four equally spaced intervals along the track.
5. The abraded track is against the entrance window of the photometer.
6. The specimen holder is positioned so that no portion of the light beam is with in 1mm of
the inside or outside edge of the track.
5. 1(a). 10 FORMULAE AND CALCULATION:
% change of transmitted light per 500 cycles
Transmitted light before test - Transmitted light after test
=
x 100
original transmitted light
5. 1(a). 11 FACTORS INFLUENCING:
a. Temperature of testing b. Humidity of Environment
c. Effect of Reinforcing Filler
d. Surface Conditions of the specimen
5. 1(a). 12 RESULT:
1. The result shall include the following.
1.1 Percentage of transmitted light that is scattered by the abrased specimens averaged for
the specimens tested.
1.2 Number of the specimens tested
1.3 Load and the number of cycles used, if other than specified.
1.4 Plot the percentage of light scattered verses cycles abraded, if more than one number
of cycles is used and,
1.5 Description of the integrating sphere photometer including, sphere geometry, exit light
beam diameter with and without the diaphragm inserted, and location of the diaphragm in
the light beam.
5.1(a).13 SAFETY PRECAUTIONS:1. Specimen should be free from burrs and other defects like grease, oil, voids and
other specimen preparation defects.
2. Weight of the specimen takes properly before and after test.
3. Don’t touch Abrasion wheals and rotating table during machine run
4. Use the brush when clean the specimen after test.
5. After test specimen should be clean properly.
6. Before and after test machine should be clean.
5. 1(a). 14 REFERENCES: ASTM Standards.
D 618 methods of conditioning plastics and electrical insulating material and testing.
D 1003 Test method for haze and luminous transmittance of transparent plastics.
D 2240 Test method for rubber property- durometer hardness.
D 691 practice for conducting and inter laboratory test program to determine the
precision of test methods.
5.1(b) ABRASION RESISTANCE FOR FLAT
SPECIMENS
5.1(b) .1 INTRODUCTION:
These test method cover the determination of the resistance to abrasion of flat surface of
plastic material measured in terms of volume loss by two different type of abrasion
testing machines as follows:
1. Test method A – Loose abrasive
2. Test method B – Bounded abrasive on cloth or paper
5.1(b). 2 DEFINITION:
Resistance to abrasion - The ability of material to withstand mechanical action such as
rubbing scrapping or erosion, that tends progressively to remove material from its
surface.
Unit :- mg/1000 cycles
5.1 (b). 3 SIGNIFICANCE AND USE:
The measurement of the resistance to abrasion of plastic material is very complex.
The resistance to abrasion is affected by many factors such as the physical properties of
the many materials, particularly hardness, resilience and the type and degree of added
filler such as cellulose, fiber or pigment. Resistance to abrasion is also affected by
condition of the test such as the nature of the abradent, action of the abradent over the
area of the specimen abradent and development and description of heat during the test
cycle.
5.1(b). 4 EQUIPMENT DETAILS:
The apparatus shall consists of following:
1. A rotating disk,
2.
A specimen,
3. Mounting plate holder,
4. Hooper and distributed for fitting fresh abrasive.
5.
Abrasives revolving counter are added weight of 4.5 kg and suitable mechanism
for driving the disk at 23.5 rpm and the specimen holder at 32.5 rpm.
Abrasion tester
5.1(b). 5 TEST SPECIMEN:
The test specimen shall measure 58.8 ± 0.4 by 72.2 ± 0.4mm and is mounted face
up on the specimen and mounting plate by means at a suitable adhesive. Wood adhesion
is obtain by holding the mount the specimen 2hrs under a 23.8 kg weight in the
conditioning room. The average at 6 measurements is taken as the abrasion less for the
material.
5.1(b).5.1 CONDITIONING:
(1) Condition the specimen at 23 ± 2°C and 50 ± 5% relative humidity for not less than
40 h. prior to test in accordance with procedure A of methods D 618 for those tests where
conditioning is required. In case of disagreement, the tolerances shall be ± 1°C and ± 2%
relative humidity.
(2) Test conditions- conduct tests in the standard laboratory atmosphere of 23 ± 2°C and
50 ± 5% relative humidity, unless otherwise specified in the test methods. In case of
disagreement, the tolerances shall be ± 1°C and ± 2% relative humidity.
5.1(b). 6 TEST PROCEDURE:
(1) Determine the density of material to be tested in accordance with standard analytical
procedure.
(2) Fill the abrasive container with the grit and adjust the rate at feed to 44 ± 2 g/min.
(3) Weigh the mounted test specimen to the nearest 0.1 g, and attach to the specimen
plate holder by means of the endcam provided.
(4) Place the weight on the specimen shaft bush at grid under the specimen, place the 1.6
mm spacer under the specimen with the largest dimension on the surface at the rotating
disk, and adjust the cam follower to this max. Tilt. Remove the spacer.
(5) For continuing runs reattach the specimen mounting plate to the specimen plate
holder. Read just to a 1.6mm lift.
5.1(b). 10 RESULTS
(1) The resistance to abrasion is the abrasion loss in volume at 1000 revolutions.
(2) The average volume loss in cm3 at 1000 revolution for the three specimens tested in
duplicate.
(3) The 95% confidence limits.
(4) The name and grade of abrasive grit employed in making the test.
5.1(b). 11 REFERENCES:
(1)- ASTM Standards
D 618 Method of conditioning plastic and electrical insulating materials for testing.
E 11 specification or wire cloth sieves for testing purpose
(2)- ASTM Standards special technical publication ASTM manual on quality control of
materials
ASTM STP 15-C. 1951.
5.2. HARDNESS TEST
5.2. 1 INTRODUCTION:
The popularity of hardness test is clearly due to the relative simplicity of
this type of measurement and its success in quality control applications acts as an indicator
surface durability. This test method covers two procedures for testing the indentation hardness
of plastic and related plastic electrical insulating material by means of the Rockwell hardness
tester. Hardness measurement of plastics usually is forcing a standard indentor – often a
hardened steel ball under a known load into a flat surface of material and measuring the degree
of penetration.
5.2. 2 (a) DEFINITION:
Hardness:- Hardness is defined as the “resistance of a material to deformation”
particularly permanent deformation, indentation, or scratching.
Unit:- Rockwell Hardness – Number reading in M, L or R scales
Durometer Hardness – Number
5.2.2
(b) Types :- Following are some of the method used for measuring the hardness
of plastics(1) Shore durometers :- These tests measure the depth of penetration under load when a
hardness steel indenter is forced into a surface by calibrated spring.
(2) Rockwell hardness tester: - Rockwell hardness number is not a measure of total
indentation but of the non-recoverable indentation after a major load applied for 15
second is reduced to a 10 kg minor load for 15 second. Measurement is made from the
increase in depth of impression when load on a ball indenter is increased from a fixed
minimum to a specified maximum then returned to the minimum load.
(3) Barcol Tester :- Barcol tester is a hand pressed one with a spring loaded plunger.
Indenter is a frustum of 26 cone with flat tip 0.0062 inch surrounded by concentric
sleeve. The indenter is mob and hardened steel. The hardness value is the initial highest
dial reading.
(4) Brinell Hardness method:- The brinell test for plastics generally used loads of 500 Kg
and a 10 mm diameter steel ball applying the load for 30 second specimen should be 0.125”
thick.
2F
Brinell Hardness =
π D2 {1-[1-(d/D)2 ]½}
Where
F = Load in Kg
D = Diameter of indenter
d = Diameter of impression produced
5.2. 3 SIGNIFICANCE:
(1)
A Rockwell hardness number is a number derived from the net increase in depth
impression as the load on an indenter is increased from a fixed minor load to a major load
and then returned to a minor load. Indenters are round steel balls of specific diameters.
Rockwell hardness numbers are always quoted with a scale used. This test method is
based on test method E18. Each Rockwell scale division represents 0.002-mm
(0.00008in) vertical movement of the indenter.
(2) A Rockwell hardness number is directly related to the indentation hardness of a
plastic material, the higher the reading the harder the material. Hardness number is equal
to minus the instrument reading. Due to a short overlap of Rockwell hardness scales, two
different dials reading on different scales are technically correct.
5.2. 4. TEST METHODS: Test Method for Rockwell Hardness of Plastic &
Electrical Insulating Material. ASTM D 785, JISK-7112, ASTM D 2240,
ASTM D 2583
At least five hardness tests are made on isotropic material for anistropic materials, at
least five hardness test is made along each principle axis of anisotropy, provided the
sample size permits.
5.2. 5 TEST SPECIMEN
5.2. 5 (a) Specimen Preparation Method
¨ The standard test specimen shall have a minimum thickness of 6mm (1/4 in) unless it is
verified that, for the thickness used, the hardness values are not affected by the supporting
surface and that no imprint shows on the under surface of the specimen after testing.
¨
The specimen is a piece cut from a moulding or sheet or composed of a file-up of
several pieces of the same thickness, provided that precaution is taken that the surface of
the pieces are in total contact and not held apart by sink marks burrs from saw cuts or
other protrusions.
¨ Care is taken that the test specimen has parallel flat surface to ensure good seating on
the anvil and thus avoid the deflection that is caused by poor contact.
5.2. 5(b) Dimensions of test specimen
The specimen is at least 25 mm square if cut from sheet stock, or least 6 cm2 in
area it cut from other shapes. The minimum width is 13 mm (1/2 in.). The diameter of the
solid rod specimen is not less than three times the diameter of the steel ball indenter.
5.2. 6 EQUIPMENT/ INSTRUMENT DETAILS:
Rockwell hardness tester, a flat anvil at least 50mm (2in) in diameter is used as a base
plate for flat specimens.
(1)
For Rockwell hardness testing, it is necessary that the major load, when fully
applied, be completely supported by the specimen and not held by other limiting elements
of the machine. To determine whether this condition is satisfied, the major load is applied
to the test specimen. If an additional load is then applied, by means of hand pressure on
the weights, the needle should indicate an additional indentation.
(2)
If this is not indicated, the major load is not being applied to the specimen, and a
long-stroke machine or less severe scale is used. For the harder materials with a modulus
around 5500Mpa (8 x 105 Psi) or over, a stroke equivalent to 150 scale divisions, under
major load application, is adequate; but for softer materials the long-stroke (250 scale
divisions under major load) machine is required.
(3)
A V- block anvil or double roller anvil is used if solid rods are tested.
5.2.6 (1) CONDITIONING:
1. Conditioning the test specimen at 23 ± 2°C and 50 ± 5% relative humidity for not less
than non prior to test in accordance with procedure A of methods D 618m, unless it has
been shown that conditioning is not necessary. Increases of disagreement, the tolerances
shall be 1°C and 2% relative humidity.
2. Test condition – conduct tests in the standard laboratory atmosphere of 23 ± 2°C and
50 ±5 % relative humidity, unless otherwise specified in the test methods or in the
specification. In case of disagreement, the tolerance shall be 1°C and 2 % relative humidity.
5.2. 7 TEST PROCEDUES:
5.2. 7(a) Rockwell Hardness
Test Method for Rockwell Hardness of Plastics and Electrical Insulating Materials
(ASTM D 785)
¨ The specimen is placed on the anvil of the apparatus and minor load is applied by
lowering the steel ball onto the surface of the specimen.
¨ The minor load indents the specimen slightly and assures good contact.
¨ The dial is adjusted to zero under minor load and the major load is immediately
applied by releasing the trip lever.
¨ After 15 sec the major load is removed and the specimen is allowed to recover for
an additional 15 sec.
¨ Rockwell hardness is read directly off the dial with the minor load still applied.
Rockwell hardness tester
5.2.7(b) Durometer Hardness
 Test Method for rubbery Property – Durometer Hardness (ASTM D 2240) The test
is carried out by placing specimens on a hard flat surface.
 The pressure foot of the instrument is pressed onto the specimen, making sure that it
is parallel to the surface of the specimen.
 The durometer hardness is read within 1sec after the pressure foot is in firm contact
with the specimen.
 Two types of durometers are most commonly used –Type A & Type D.
 The difference between two types is the shape and dimension of the indentor.
 Type A durometer is used for soft material.
 Type D durometer is used for hard material.
Durometer hardness tester
5.2.9 FORMULA & CALCULATIONS:
(1) Calculate the arithmetic mean for each series of tests on the same material and
at the same set of test conditions. Report the results as the “average value”
rounded to the equivalent of one dial division.
(2) Calculate the standard deviation (estimated) as follows, and report it to two significan
figures:
S=
(ε x2 – n x2 / (n-1)
Where:
S = estimated standard deviation
X = value of a single observation,
X = arithmetic mean of a set of observation ,and,
n = number of observation in the set.
5.2. 10 FACTORS INFLUENCING:
(1) Temperature of testing
(2) Humidity of Environment Sensitive material.
(3) Effect of Reinforcing Filler
(4) Surface Conditions of the specimen
(5) An-isotropy
5.2. 11 RESULT:
The report shall include the following:
(1) Material identification,
(2) Filler identification and particle size, if possible,
(3) Total thickness of specimen,
(4) The number of pieces in the specimen and the average thickness of each piece,
(5) Surface conditions, for example, molded or machined, flat or round,
(6) The procedure used (procedure A or B),
(7) The direction of testing,
(8) A letter indicating the Rockwell hardness scale used,
(9) An average Rockwell hardness number calculated by procedure A or B,
(10) The standard deviation.
5.2.12 SAFETY PRECAUTIONS:1) The load should be taken according to correct scale.
2) Specimen should be flat.
3) The diameter of ball should be according to the scale.
5.2. 13 REFERENCES: ASTM standards:
D 617 test method for punching quality of phenolic laminated sheets
D 618 methods of conditioning plastic and electrical insulating materials for testing
D 2240 test method for rubber property-durometer hardness
E 18 test methods for Rockwell hardness and Rockwell superficial hardness of metallic
materials
E 691 practice for conducting an inter laboratory test study to determine the precision of test
methods.
5.3. COEFFICIENT OF FRICTION
5.3.1 DEFINITIONS:
5.3.1(a) Coefficient of friction- It is the ratio of the frictional force to the force, usually
gravitational acting perpendicular to the two surfaces in contact. This coefficient is a
measure of the relative difficulty with which the surface of one material will slide over an
adjoining surface of itself or of another material.
5.3.1(b) Friction: The resisting force that arises when a surface of one substance slides or
tends to slide over an adjoining surface of itself or of another
substance.
There are two types of friction:
(1) The resistance opposing the force required to start to move one surface over another.
(2) The resistance opposing the force required to move one surface over another at a
variable, fixed or predetermined speed.
5.3.1(c) Slip: It denotes the lubricity of two surfaces sliding in contact with each other
5.3.2 SIGNIFICANCE AND USE:
(1) Measurements of frictional properties are made on a film or sheeting specimen when
sliding over itself or another substance. The coefficients of friction are related to the slip
properties of plastic films that are of wide interest in packaging applications.
(2) Slip properties are generated by additives in some plastic films for e.g. Polyethylene.
These additives have varying degrees of compatibility with the film matrix. Some of them
bloom, or exude to the surface, lubricating it and make it more slippery.
(3) Frictional and slip properties of plastic film and sheeting are based on measurement of
surface phenomena where products have been made by the same process, their surface is
dependent on the equipment or its running conditions.
(4) The measurement of the static coefficient of friction is highly dependent on the rate of
loading and on the amount of blocking occurring between the loaded sled and the platform
due to variation in time before motion is initiated.
5.3.3 EQUIPMENT DETAILS:
The following equipments are use for testing,
1.
Sled
2.
Plane
3. Scissors or cutter
4. Adhesive tape
5. Beaded chain
6. Low-Friction pulleys
7. Force- Measuring Device
8. Supporting Base
9. Driving or pulley Device for sled or Plane
5.3.3. (1) CONDITIONING:
Condition the test specimens at 23 ± 2°C (73.4 ± 3.6°F) and 50 ± 5% relative
humidity for not less than 40 h prior to test in accordance with procedure A of methods D
618. In case of disagreement, the tolerances shall be ± 1°C (± 1.8°F) and ± 2% relative
humidity
5.3.4. TEST METHODS:
Test Method for Static and Kinetic Coefficients of Friction of Plastic Film and
Sheeting (ASTM D 1894)
5.3.5 TEST SPECIMENS:
The specimens are prepared as following,
1.
For plane specimen – cut 250 mm in the machine direction and 130 mm in the
transverse direction
2. For film specimen – cut 120 mm square
3. For sheet specimen – cut 63.5 mm square
5.3.6 TEST PROCEDURES:
(1) Tape the 250/130 mm film or sheet specimen to plane with the machine direction at
the specimen in the 250mm direction.
(2) Smooth the film specimen to eliminate wrinkles if necessary taking care not to alter
the specimen surface through finger oils etc.
(3) Start the driving mechanism which is adjusted previously provides a speed at 150 ±
30mm/mm per min.
(4) Record the visual average reading during the run at app. 130mm where the surfaces
are sliding uniformly over one month.
(5) This is equivalent to the kinetic force require to sustain motion between the surface
normally lower than the static force required to initiate motion, after the sled has traveled
over 130mm over stop the apparatus.
(6) Remove the film or sheeting from the sled and the horizontal plane.
(7) The apparatus is now ready for the next set of specimens.
(8) A new set of specimens is used for each run. Specimen surface(s) is tested more than
once unless such tests constitute one of the variables to be studied.
5.3.7 FORMULAE:
(1) Calculate the static coefficient of friction μs , follows
μs = As/ B
where, As = initial motion scale reading, g, and
B = sled weight, g.
(2) Calculate the kinetic coefficient of friction μk , follows
μk = Ak/ B
where, Ak = average scale reading obtained during uniform sliding of the film surfaces,g ,
and
B = sled weight, g.
(3) Calculate the arithmetic mean of each set of observation and report these values to three
significant figures.
(4) Calculate the standard deviation (estimated to be ±15% of the value of the coefficient of
friction) as follow and report it to two significant figure.
S=
(X
X2 –n X2 / (n-1)
(n-1)
Where
S = sample standard deviation
X = value of a single observation
n = number of observation and
X = arithmetic mean of the set of observations.
5.3.8 FACTORS INFLUENCING:
a. Surface Conditions of the specimen
b. A smooth moulded surface yield lower value than a machined surface.
c. Test Speed- Higher the test speed is directly proportional to the values coefficient of friction.
d. Sled Weight- Sled Weight inversely proportional to the values coefficient of friction.
5.3.9 RESULTS
The report shall include the following
(1) Complete description of the plastic sample, including manufacturers code designation,
thickness, material, production, surfaces tested, principal direction tested, approximate age of
sample after manufacturer.
(2) Description of second substance if used
(3) Apparatus used
(4) Average static and kinetic coefficient of friction together with the standard deviation, and
(5) Number of specimen tested for each coefficient of friction.
5.3.11SAFETY PRECAUTIONS:
1. Level of Instrument should be horizontal
2. Slides should be smooth and free from rust etc.
3.
Specimen should be free from oil, grease, pinholes and wrinkle.
5.3.12 REFERENCES: ASTM standards
D 618 Method of conditioning plastic and electrical insulating materials for testing.
D 883 definition of terms relating to plastics
D 3574 Methods of testing flexible cellular materials slab banded and molded urethane
foams.
E 691 Practice for conducting an inter laboratory test study to determine the precision of
test Methods.