Materials Science & Engineering for Mechanical Engineers
Lecture 5: Material Testing
Material Testing
➢ Materials testing is a well-established technique used to
determine the physical and mechanical properties of raw
materials and components from a human hair to steel, composite
materials and ceramics.
Reasons for Material Testing
● Meeting requirements of regulatory agencies
● Selecting appropriate materials and treatments for an application
● Evaluating product design or improvement specifications
● Verifying a production process
Types of Material Testing
1. Destructive Testing / Mechanical Tests
➢ The material may be physically tested to destruction or
indentation
➢ To measure the strength, hardness, toughness, etc.
➢ Examples: tensile testing, impact testing, hardness testing,
etc.
2. Non-destructive Tests
➢ Samples or finished articles are tested before being used and as
routing maintenance checks
➢ Example: Radiography, Dye penetration test, etc.
Tensile Test
➢ A tensile test applies tensile (pulling) force to a material and
measures the specimen's response to the stress. By doing this,
tensile tests determine how strong a material is and how much it
can elongate.
➢ Is done on a Universal Testing Machine (UTM)
➢ Variables such as strain, stress, elasticity, tensile strength,
ductility, and shear strength are measured and computed.
➢ Test specimens can be round or flat.
➢ Standard for Tensile testing: ASTM A370
ASTM A370
➢ is a testing standard that covers the mechanical testing
definitions and procedures of steel products such as
wrought and cast steels, stainless steels, and related alloys.
Universal Testing Machine (UTM)
➢ A machine which applies a
tensile force (a force applied in
opposite directions) to the
specimen, and then measures
that force and also the
elongation.
➢ Uses a load cell and an
extensometer
to
apply
measured force to a test
specimen
and percentage
elongation, respectively
➢ This machine usually uses a
hydraulic cylinder to create the
force. The applied force is
determined
by
system
pressure,
which
can be
accurately measured.
Tensile Test Results
Cup and cone fracture signifies a ductile material.
A shear fracture indicates a brittle material.
Hardness Testing
➢ Hardness is the ability of a metal or metal alloy to resist plastic
deformation, in a specific, localized location rather than in a
general location. It is also defined as metal’s resistance to
indentation, scratching, or abrasion.
➢ Hardness is an important feature because the level of hardness
that a metal has directly relates to its ability to resist wear.
➢ Hardness levels can vary within a given type of metal depending
on the alloying elements, heat treatment, work hardening, and
other hardening methods used.
➢ Methods for evaluating hardness such as Brinell hardness and
Rockwell hardness were invented to create a common
understanding of hardness levels because of the variation of
hardness among metals and even within a family of metals.
Brinell Hardness Test (BHN)
➢ Brinell hardness is a scale used to provide a numerical value to
the level of hardness of a material.
➢ The method for conducting a Brinell hardness test is defined fully
in ASTM E10.
➢ A certified Brinell indenter is pressed against a metal under a
predetermined load for a predetermined amount of time. All of
this is specified to reduce the risk of experiment method variation
affecting results.
➢ Typically, the indenter is a 10mm ball of hardened steel and
the force is 3,000 kgf for steels and other similar materials.
➢ For softer or harder materials, the test changes slightly. The
indenter is removed after it is applied onto the metal with a force,
and the resulting width of the indentation is measured using a
microscope.
➢ The measurement of the indentation can then be converted into a
Brinell hardness value using a Brinell hardness scale.
Rockwell Hardness Test (HRC)
➢ The Rockwell hardness test is the most employed hardness test
method. It is used on all kinds of metals, except in situations
Rockwell Hardness Test (HRC) vs Brinell Hardness Test (BHN)
What is the Difference Between Rockwell and Brinell Tests?
➢ The Brinell hardness testing uses a 10mm hardened steel
where the surface conditions and metal structure would produce
ball, while the Rockwell test uses either a much smaller steel
high variations.
ball (<4mm) or a diamond cone, depending on the material
➢ The exact method can be found in ASTM E18.
being tested.
➢ Rockwell hardness tests are performed with an indenter of a
➢ The Rockwell test measures the depth of the indentation, while
specified size applied with a specified force for a predetermined
the Brinell test measures the width of the indentation. Rockwell
amount of time.
hardness tests use a preload to establish a zero position before
➢ The measurement of the indentation is then converted to a
Rockwell hardness value using a Rockwell hardness scale.
the main load is applied. The main load is then taken away and
only the preload remains. Then the distance traveled is measured
by the Rockwell testing machine.
Test Method Illustration
A = Depth reached by indenter after application of preload (minor load)
B = Position of indenter during Total load, Minor plus Major loads
C = Final position reached by indenter after elastic recovery of sample material
D = Distance measurement taken representing difference between preload and
major load position. This distance is used to calculate the Rockwell Hardness
Number.
➢ The conversion scales for Rockwell hardness and Brinell
hardness are not the same and should not be confused with
one another.
Vickers Hardness Test (HV)
➢ It is a test performed to measure the hardness of materials,
specifically thin sections and small parts.
➢ It is comprised of a diamond indenter and a light load to
produce an indentation on the subject under testing.
➢ The depth of indentation is converted into the hardness value of
the object.
➢ The smaller the indentation, the harder the object. Likewise, if
the indentation is large, the material is lacking in hardness.
➢ This test is utilized by many industries to determine the right type
of material to use for operations and machinery. A material with
ideal hardness according to its purpose should be chosen.
➢ The Vickers hardness test is also known as microhardness
testing.
Impact Testing
➢ Impact testing is testing an object's ability to resist high-rate
loading.
➢ An impact test is a test for determining the energy absorbed in
fracturing a test piece at high velocity.
Impact Testing – Pendulum
➢ A pendulum impact testing is used to determine the impact
strength or toughness of a material under impact loading by
measuring the amount of energy the material is able to
absorb.
➢ It is commonly thought of as one object striking another object at
➢ Understanding a material’s energy absorption properties is critical
a relatively high speed. The two primary forms of impact test are
in predicting how much plastic, or permanent, deformation the
drop weight and pendulum impact tests.
material will be able to withstand before failure and is an
important
Impact Testing – Drop Weight
consideration
in
research
and
development
applications as well as for quality control and material acceptance
purposes.
Fatigue Testing
➢ A drop weight impact test typically determines a material's
resistance to a sudden external force.
➢ This type of test is also applicable for pipe testing where the
impact resistance of thermoplastic pipes is measured.
➢ The standards which are applicable for this type of testing include
ASTM D2444 and ISO 3127.
➢ Fatigue testing applies cyclic loading to a test specimen to
understand how it will perform under similar conditions in
actual use.
➢ The load application can either be a repeated application of a
fixed load or simulation of in-service loads.
➢ The load application may be repeated millions of times and
up to several hundred times per second.
Non-destructive Testing
1. Radiographic Testing (RT)
2. Dye Penetration Testing (DPI)
➢ A non-destructive testing (NDT) method which uses either x-rays
or gamma rays to examine the internal structure of
manufactured components identifying any flaws or defects.
➢ The test-part is placed between the radiation source and film
(or detector). The material density and thickness differences of
the test-part will attenuate (i.e. reduce) the penetrating radiation
through
interaction
processes
involving
scattering
and/or
absorption.
➢ The differences in absorption are then recorded on film(s) or
through an electronic means.
➢ In industrial radiography there are several imaging methods
available, techniques to display the final image, i.e. Film
Radiography, Real Time Radiography (RTR), Computed
Tomography (CT), Digital Radiography (DR), and Computed
Radiography.
➢ This non-destructive testing technique, also known as liquid
penetrant inspection (LPI), is a cost-effective method used to
locate surface breaking flaws such as cracks, porosity, laps,
seams and other surface discontinuities.
➢ Dye penetrant inspection can be applied to both ferrous and
non-ferrous materials and all non-porous materials (metals,
plastics or ceramics).
➢ It is commonly used to detect defects in castings, forgings
and weldments.
➢ Applications: aerospace, power generation, petrochemical
and oil, and gas
3. Magnetic Particle Testing (MPT)
➢ also referred to as Magnetic Particle Inspection, is a
nondestructive examination (NDE) technique used to detect
surface and slightly subsurface flaws in most ferromagnetic
materials such as iron, nickel, and cobalt, and some of their
alloys.
➢ because it does not necessitate the degree of surface
preparation required by other nondestructive test methods,
conducting MPT is relatively fast and easy. This has made it
one of the more commonly utilized NDE techniques.