MARMARA UNIVERSITY
FACULTY OF ENGINEERING
MECHANICAL ENGINEERING DEPARTMENT
ME 4001
MECHANICAL ENGINEERING LABORATORY REPORT
EXPERIMENT NO : 1
EXPERIMENT NAME : TENSILE TESTING of ENGINEERING
MATERIALS
Experiment Date:25.02.2019
Report Date: 04.03.2019
Students Names and Numbers:
Ozan Berke YABAR 150416822 (Leader)
İhsan ÇAKMAK 150414021
Şahin AKGÜN 150414057
2 ) Scope of Test
The objective of this experiments is to load a tensile test sample at a constant crosshead speed
until failure, while recording the value of the load and the change in length of the test sample
at each stage. Then based on the collected data,
• The material’s stress-strain relationship is obtained.
• The following structural properties are determined: Modulus of elasticity, yield strength,
ultimate tensile strength, yield strain, failure strength and strain to failure.
• The strain is measured with a video extensometer.
• The reduction of cross-sectional area of the tested sample is determined, if applicable.
3 ) Apparatus :
 Universal Testing Machine (SHIMADZU AGS-X 50 kN)
 Computer with TRAPEZIUM Software
 Video Extensometer
 Vernier Caliper
 Permanent marker
4) Materials :
Dog bone shape High Density Polyethylene(HDPE) polymer specimen (TS EN
ISO 527 Standards)
5) Theory
Tensile test, is a basic and universal engineering test for achieve material
parameters such as ultimate strength, yield strength, elongation, area of
reduction and Young’s modulus. As a mechanical engineering student and also
for designing machines, one of the most important thing is obtain your
mechanical part’s limits. We have to know when will our parts fail. With tensile
test we can obtain our part’s strength limits.
With tensile test we can obtain our material is acting like a Brittle or
Ductile material. It is also important because when we are doing fatigue
analysis, we need this information to calculate our part’s life.
By looking the Stress-Strain curve we can compare the strength of
different materials, independently of their sizes.
6) Definitions and Process Terminology
 Stress : Stress is defined as the force per unit area of a material.
i.e. Stress = force / cross sectional area
We can calculate stress with this formula
 
F
A
F is the force and A is the cross sectional area.
 Strain : Strain is defined as extension per unit length. Strain = extension /
original length. We can calculate strain with the formula below.

L  L0
L0
where L is the instantaneous length of the specimen and L0 is the initial length.
 Proportional Limit : Proportional limit is point on the curve up to which
the value of stress and strain remains proportional. From the diagram point
P is the called the proportional limit point or it can also be known as limit
of proportionality. The stress up to this point can be also be known as
proportional limit stress. Hook’s law of proportionality from diagram can
be defined between point OP. It is so, because OP is a straight line which
shows that Hook’s law of stress strain is followed up to point P.
 Elastic Limit : Elastic limit is the limiting value of stress up to which the
material is perfectly elastic. From the curve, point E is the elastic limit
point. Material will return back to its original position, If it is unloaded
before the crossing of point E. This is so, because material is perfectly
elastic up to point E.
 Breaking Stress (Point of Rupture) : Breaking point or breaking stress is
point where strength of material breaks. The stress associates with this
point known as breaking strength or rupture strength. On the stress strain
curve, point B is the breaking stress point. Here is Curve 1.
 Modulus of elasticity : An elastic modulus (also known as modulus of
elasticity) is a quantity that measures an object or substance's resistance to
being deformed elastically (i.e., non-permanently) when a stress is applied
to it. The elastic modulus of an object is defined as the slope of its stress–
strain curve in the elastic deformation region.
 Yield Strength : Yield strength or Yield stress is the material property
defined as the stress at which a material begins to deform plastically
whereas yield point is the point where nonlinear (elastic + plastic)
deformation begins.
Prior to the yield point the material will deform elastically and will return
to its original shape when the applied stress is removed. Once the yield
point is passed, some fraction of the deformation will be permanent and
non-reversible.
 Ultimate tensile strength : is the capacity of a material or structure to
withstand loads tending to elongate, as opposed to compressive strength,
which withstands loads tending to reduce size. In other words, tensile
strength resists tension (being pulled apart), whereas compressive strength
resists compression (being pushed together). Ultimate tensile strength is
measured by the maximum stress that a material can withstand while being
stretched or pulled before breaking.
 Here the below, stress-strain curve for ductile materials (Curve 2)

7) Procedure
For dog bone shape specimen, my department professors use iron mold and they
cut it the material for desired shape.
Photo 1 : Iron mold for to get dog bone shape HDPE material.
Photo 2 : Dog bone shape HDPE. They determine the dimensions according to
TS ISO EN 527.
We need to cut the specimen according to standards because we need to
sure the results of the tests will be the same all around the world. That is why we
used the TS ISO EN 527 standards.
We are using dog bone shape because we need to see the elongation on
the gage length part. Also the specimen has radius because we don’t want the
stress concentration on our specimen.
Before the test we measure the thickness of our specimen. We found 2.94,
2.96 and 3.00 mm on different zones. Then we calculate the average value
which is 2.97 mm.
Calibration is really important for the accurate results. Before starting the
test, we calibrate the universal testing machine. We press the force zero hold
button on computer and we connect the specimen to the testing machine.
Photo 3 : Universal Testing Machine (SHIMADZU AGS-X 50kN)
When we are connecting the specimen to the testing machine we have to
be sure our materials axis and the computer camera’s axis has to intersect.
Otherwise it could be some bending moment and we our calculation’s will be
wrong because of the bending effect.
Photo 4 : When we were trying to intersect the axis of camera and specimen
For strain calculations, we need gage length. Because of this purpose we
used these clips. We see that our gage length is 66 mm.
Photo 5 : We use these clips to obtain the gage length.
Using these clips we can see the engineering stress, real stress and also the
dimensions.
Photo 6 : Orange and green boxes is for obtain the point of elongation and it
measure how much is it. Pink box is for measuring the width instantly.
.
Photo 7 : We can see the displacement and width values just below the camera
image. We want to keep them blue for to sure it is safe.
After our specimen reaches the fracture stress level, it has broken. We
calculate the strain and elongation with computer.
Photo 8 : Photo of our specimen after tensile test.
After the tensile test, we notice some white parts as shown in photo 9
Photo 9 : All of the specimens has the stress whitening.
Stress whitening is a white line appearing along the bend or curve when a
material is stressed by bending or punching operations. The appearance of white
line indicates that there is an onset of failure of the corresponding material. This
phenomenon is known as "stress whitening". This is more common in
amorphous materials, and also in some brittle polymers like PS, PMMA and
Polycarbonate. The white colour is because of the light scattering by the crazes.
Stress whitening starts when stress is created by impact or tension upon a
polymeric surface. This stress leads to the creation of microcrazes and/or
microvoids—essentially, the microscopic beginnings of cracks that result when
stresses overcome the forces bonding particles together. Unlike surface cracks,
you cannot feel micro- crazes or microvoids, but you can see them. This is
because these tiny aberrations reflect light slightly differently than the surfaces
around them, which in turn gives them different color- ation as perceived by the
human eye.
You can see the difference between our test specimen and the original
specimen. Also we can see the elongation and stress whitening physicaly.
Photo 10 : Difference between test specimen and the original one
Photo 11 : Difference between our specimen and metal specimen.
We can notice that the test specimens not homogeneous. As you can see that
from photo 9, all of them broke from different parts. It means they are not
homogeneous.
If we compare our specimen with the metal specimen at photo 11, we can see
the main difference is how much necking the metal specimen and also testing
this ductile metal specimen takes too much long time than testing our specimen.
In tensile test we observed when the ductile materials fractured we can see the
necking on our material as we described at Curve 2. (Stress-strain curve for
ductile materials) But for the brittle materials on tensile test there won’t be any
necking part.
8) Raw Data
9) Calculations and Results :
10) Figures and Diagrams
11)Discussion
12)Conclusion
13)Referances
Mechanics of Materials – R.C. Hibbeler 9th Edition
http://www.engineeringintro.com/mechanics-of-structures/stress-strain-curveexplanation/
http://web.mit.edu/course/3/3.11/www/modules/ss.pdf
https://www.mtu.edu/materials/k12/experiments/tensile/
https://www.ptonline.com/articles/how-to-prevent-stress-whitening-in-ppcopolymers
https://en.wikipedia.org/wiki/Elastic_modulus
https://en.wikipedia.org/wiki/Ultimate_tensile_strength
https://en.wikipedia.org/wiki/Stress-whitening