Question

During the experiment a constant tensile load was applied to the sample, as described in Study session 17.1. This caused the sample to extend. You measured the change in length of the sample over time, which enabled you to calculate the strain.

In Question 2a you are asked to calculate the stress acting on parts of a sample at the beginning and end of an experiment similar to that in Week 17. The load applied in the experiment was 5.1 kN.

All your answers to Question 2a should be given to 3 significant figures, in appropriate units.

a.

i.To calculate the stress on the sample due to the applied tensile load you need to know the area over which this force is acting. Using information from Figure 2, show that the relevant cross-sectional area of the sample within the gauge length at the start of the experiment is 50.3 mm2.

ii.Using the value for the cross-sectional area from Question 2a(i), calculate the stress experienced by the test specimen within its gauge length, at the start of the test.

iii.The applied load remains constant throughout the test. At the end of the test, the diameter of the test specimen shown in Figure 1 at the location where necking occurred was measured and the cross-sectional area calculated to be 16.0 mm2. Based on the reduced cross-sectional area at the necking location, calculate the stress in the neck at the point of failure.

iv.Compare the value of stress at the beginning of the test (your answer to Question 2a(ii)) with the stress value at the point of failure (your answer to Question 2a(iii)) and use these values to calculate the percentage increase in the value of stress due to ‘necking’ of the test specimen from the start of the test to the point of failure

Answer 1