TENSILE PROPERTIES OF MATERIALS
The student should read this practical and complete the Table below (Estimation of maximum forces for testing) prior to your practical session.
ROOM, M1-09, Common Testing – assemble in building foyer
CLOSED FOOTWEAR MUST BE WORN. YOU WILL NOT BE ALLOWED TO DO THE PRACTICAL IF YOU DO NOT HAVE CLOSED FOOTWEAR.
Only hand up this and the following pages.
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AIM
To investigate the range of tensile properties of various materials and to appreciate the importance of properties in design.
PROCEDURE
Various materials will be provided in a suitable form for tensile testing.
The dimensions of each test piece are to be recorded to allow for the later calculation of the cross sectional area, So, (that is the area over which the force is applied). The original gauge length, Lo, is to be marked on each sample.
From an estimated tensile strength of each material being tested and the given approximate cross sectional area (see table below), calculate the estimated maximum forces and hence the required force range for testing (HINT Use the formula for stress!)
Material Estimated tensile
strength
(MPa) Approximate cross sectional area
(mm2) * Estimated maximum force required
(N)
polyethylene 20
polystyrene 35
polystyrene-butadiene HIPS 30
nylon 66 55
polypropylene 25
glass reinforced polypropylene (composite) 60
Acronitrile Butadeine Styrene ABS 40
Polycarbonate 70
cold worked brass 420
annealed aluminium 100
cold worked aluminium 180
low carbon steel 230
* approximate only – must not be used in calculation on the following page
A tensile test is to be performed on each of the provided samples. For each test, the force coinciding with the elastic limit, the maximum force and the final gauge length, Lf, should be recorded. Each student then needs to fill in the following tables from the supplied data set.
RESULTS:
Tabulate the raw data using the table below.
Material and condition
(if relevant) Original dimensions
(mm) * Force at the limit of proportionality
(kN) Maximum force
(kN) Initial gauge length, Lo
(mm) Final gauge length, Lf
(mm)
Your Polymer
Steel
Aluminium
Brass
(*) specify whether width and thickness or diameter.
Generate schematic force/extension curves using Excel on the same graph and axes (i.e. superimpose the graphs for the different materials), of the materials tested to qualitatively evaluate their relative rigidities. Clearly identify each material on the graph. Note variations in the cross sectional area will affect the measured properties and this will NOT be reflected in the force-extension curves.
Note that if your polymer has a particularly long elongation you may have to use a second X Axis on the plots (at the top of the Chart) or use a Logarithmic Scale for the X Axis.
Calculate properties using the table below. Report the area to 2 decimal places and the properties as whole numbers.
Material Original cross sectional area
(mm2) Limit of proportionality
(MPa) Tensile strength
(MPa) % elongation
Your polymer
Steel
Aluminium
Brass
From the force extension data generate schematic Stress/Strain extension curves using Excel.
From suitable references, enter in the table below published mechanical properties for the materials tested by your practical group. Ensure that you quote all references used.
Material
Elastic limit
(MPa) Tensile strength
(MPa) %
Elongation Reference
Number
Brass
Steel
Aluminium
Your Polymer
Give full details of references used at the end of the report. References in practical reports must follow a standard format.
Note:
1. When describing the material sufficient details must be given to fully identify material and its condition. For metals this will include its composition (or standard designation e.g. 1010 steel) and its condition such as level of cold working (e.g. 50% reduction cold worked, or half hard or H04 temper) or heat treated condition (e.g. annealed). ASM Handbook volume 2 (pages 21, 25, 26 and 49 for aluminium alloys and pages 234, 235, 265? for copper alloys) is a good references for properties of aluminium, copper and copper alloys in different conditions (tempers).
2. Elastic limit is being used as an estimate of yield strength (or proof strength) and published data will most often refer to yield (or proof) strength.
3. Polymers may only quote either yield or tensile strength. Provide any relevant comments on your results. Some points which you may wish to consider:
• Are the results what you expected (do they follow the trends of data in your references?).
• For alloyed metals (e.g. brass, steel if tested) can you suggest the alloy composition and condition by comparison with data in references?
• Compare polymers with respect to their strength, ductility and expected rigidity
Do NOT focus on inaccuracies or class mistakes.
From the stress-strain characteristics, as indicated by your Excel Plots, rank the relative tensile toughness levels of the materials tested giving your reasons.
Give full details of any text books, periodicals, standards, web sites and personal contacts that may have been used. References in practical report must follow the Harvard standard format.
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