Inspect the motorised tensometer, noting the settings that can be made and the method of plotting results on the attached chart recorder.
CIE5003- Materials
Laboratory testing – TESTS ON POLYMERS
Purpose
- To investigate the strength of various polymers.
- To investigate the effect of strain rate on polymer strength.
Safety Precautions
- The motorised tensometer has moving parts. Assess yourself and your colleagues for loose clothing, jewellery or long hair that might get trapped in the tensometer.
- Energy is released when the polymers break. Always close the cover n the tensometer before running a test.
Apparatus:
Motorised tensometer with attached chart recorder.
Micrometer.
Stop watch.
Three sheets of chart paper.
Graph paper
Material Samples (coloured to help identification): Two each of:
Yellow Low density polyethylene (LPDE). Polythene, amorphous with crystalline regions.
Nominal density 920 kg/m3
Red High density Polyethylene (HDPE), crystalline with amorphous regions
Nominal density 960 kg/m3
White Polyamide (PA). Nylon, crystalline
Nominal density 1130 kg/m3
Black Glass-filled Polyamide, crystalline, with powdered glass filler.
Nominal density 1490 kg/m3
Introduction
Polymers have many applications in construction, including adhesives, sealants, insulators, pipes, window frames and cladding panels. They are extensively used for repairs, and may be used as additives in concrete.
The properties of polymers can be adjusted for particular applications by modifying the lengths of the molecule chains, by varying the proportion of crystalline material in the solid, or by including other substances such as filler powders or fibres.
The two major groups of polymers are:
- Thermoplastics. These soften when heated. Examples are polyethylene, polypropylene, PVC, nylon, acrylics.
- Thermosets. These harden during manufacture in a way that cannot be reversed by heating. Examples are epoxies, phenolics, polyesters and polyurethanes.
The behaviour of thermoplastics is partly viscous, ie the stress depends on the rate of strain. The aim of these tests is to stress four thermoplastics to failure and to note the influence of strain rate.
Procedure
- Inspect the motorised tensometer, noting the settings that can be made and the method of plotting results on the attached chart recorder.
Always close the cover panel before running the Tensometer.
- Set the tensometer and recorder for a maximum force of 5kN, a strain rate of 30mm per minute and a maximum extension of 100mm.
- Measure one of the specimens and note the cross-section area under test.
- Test one specimen of each colour, recording the results on the same chart. Be sure to label the traces.
For each specimen, work out:
- The ultimate tensile stress, N/mm2
- The Modulus of Elasticity
- Compare these to the respective values of steel
- Set the strain rate on the tensometer to 400 mm/minute. Test the second specimens of LDPE, HDPE and PA at this new strain rate, recording results on a new chart. Note differences from the previous behaviour.
Report
- Explain experiment, apparatus and method used.
- Report and Explain the behaviour of the sample under the applied load up to and including the point of fracture and compare with steel
- Explain the behaviour of the samples under the applied load with different strain rate
- Relate the results to published information on the properties of polymers.
Section B
TENSILE TESTING ON FIBRE REINFORCED BAR
Aims
To observe simple tensile tests on fibre reinforced polymers barsandcompare/interrogatetheirmechanical and physical properties through the use of Load/Extension
Objectives
Todescribetensiletest, record results, analyse findings and form conclusions
Health & Safety
The Denison Universal Testing Machine will be operated by an experienced technician.
- Beware not to drop steel bars on toes.
- Stand a suitable distance away from the equipment during testing.
- Be careful of sharp serrated edges of fractured samples.
Material Samples
- One fibre reinforced polymer bar.
Apparatus
- Avery Denison Universal Testing Machine.
- Micrometer.
Fibre Reinforced Bar
- Measure the diameter with the micrometer provided. Take two measurements of diameter at the length of the bar.
- Calculate the average cross sectional area (CSA) of the bar and inform the technician of the value for input into the Test Program.
Tensile Tests
Secure the samples (in turn), into the jaws of the Denison Universal Testing Machine and load each bar (in tension), to fracture. Two graphs will be provided from the tensile testing software:
- Load v extension Graph ( used for calculation purposes)
- Load v extension Graph ( used for calculation purposes)
Report
- Explain experiment, apparatus and method used.
- Explain the behaviour of the sample under the applied tensile load up to and including the point of fracture.
- Select a minimum of three points on the elastic region of each load v Extension graph and calculate the average value of Young’s Modulus of Elasticity (E) for each bar (show all calculations). Comment on the value obtained against the values that might be expected.
- Fully label the Load v Extension graphs provided and highlight the important points and values for each curve.
- Sketch and classify the fracture of both samples.
Materials laboratory level HE5
The submission consists of TWO parts;
(i) A report of requested information (75% marks)
(ii) A professional presentation (25% marks);
Working as group, plan and prepare a 20 minute presentation about testing of Steel
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