Tensil Test Experiment (Lab Report)

Introduction and Theory:
Mechanical properties required in both the design and in the manufacturing.
• In design, mechanical properties such as elastic modulus and yield strength are important
in order to resist permanent deformation under applied stresses. Thus, the focus is on the
elastic properties.
• In manufacturing, the goal is to apply stresses that exceed the yield strength of the
material so as to deform it to the required shape. Thus, the focus is on the plastic
properties
Tensile testing:
• An axial force applied to a specimen of original length (Lo) elongates it, resulting in a
reduction in the cross-sectional area from Ao to A until fracture occurs.
• The load and change in length between two fixed points (gauge length) is recorded and
used to determine the stress-strain relationship.
• A similar procedure can be adopted with a sheet specimen.
Universal tensile mashine:
Also known as a universal tester, materials testing machine or materials test frame, is used
to test the tensile strength and compressive strength of materials. It is named after the fact that it
can perform many standard tensile and compression tests on materials, components, and
structures.
Tensile testing procedure:
• In order to conduct a tensile test, the proper specimen must be obtained. This specimen
should conform to ASTM standards for size and features. Prior to the test, the crosssectional
area may be calculated and a pre-determined gage length marked.
• The specimen is then loaded into a machine set up for tensile loads and placed in the
proper grippers. Once loaded, the machine can then be used to apply a steady, continuous
tensile load.
• Data is collected at pre-determined points or increments during the test. Depending on the
material and specimen being tested, data points may be more or less frequent. Data
include the applied load and change in gage length. The load is generally read from the
machine panel in pounds or kilograms.
• The change in gage length is determined using an extensometer. An extensometer is
firmly fixed to the machine or specimen and relates the amount of deformation or
deflection over the gage length during a test.
• While paying close attention to the readings, data points are collected (force and the
change in length) until the material starts to yield significantly. This can be seen when
deformation continues without having to increase the applied load. Once this begins, the
extensometer is removed and loading continued until failure. Ultimate tensile strength
and rupture strength can be calculated from this latter loading.
• Once data have been collected, the tensile stress developed and the resultant strain can be
calculated. Stress is calculated based on the applied load and cross-sectional area. Strain
is the change in length divided by the original length.
• Upon completion of the test, the sample is reassembled and final measurements for total
elongation and minimum diameter are made using a vernier caliper.
Discussion:
1- Plot stress strain curve of material A and material B. Specify which material has yield point
phenomenon and which one is without yield point and use 0.2% offset line to find the yield point
2- Find the following:
2.1-Yield strength of material A:
2.2- Yield strength of material B:
2.3- Elastic Modulus of material A and B:
2.4- Ultimate tensile strength of material A and B:
3- Calculate the maximum load and elongation if the original diameter and length are 9.11 mm
and 50.8 mm respectively:
4- Discuss the possible errors in this test. Explain what can be done to reduce and control the
error.