Problem 3: The force-elongation data in the table below were obtained from a ten

Question

Problem 3: The force-elongation data in the table below were obtained from a tensile test of a
metal specimen with a rectangular cross-section of 0.25 in
2 and a gage length (the length over which the elongation is measured) of 3.0 inches.
3-1) Convert the force-elongation data to stress-strain data and tabulate your results.
3-2) Plot these values and draw a best-fit line to obtain a stress-strain curve.
3-3) Determine the modulus of elasticity from your best fit line.
3-4) Estimate the value of the proportional limit.
3-5) Use the 0.2% offset method to determine the yield stress.

Stress (ksi) Stress x 10^3 (in./in)
0 0
2.5 0.0825
5 0.177
7.5 0.355
10 0.508
12.5 0.7195
15 0.8575
17.5 0.996
20 1.141
22.5 1.3
25 1.4715
27.5 1.64
30 1.8165
32.5 2.0005
35 2.1935
37.5 2.3205
40 2.444
42.5 2.666
45 2.93
47.5 3.181
50 3.652
52.5 4.041
55 4.528
57.5 5.666
60 7.066
62.5 10.5025
65 14.448

Explanation / Answer

a)stress =F/A given A=0.25 in2

strain =l/l given l=3 in

so the table can be made

b) you can plot the stress(y-axis) vs strain(x-axis) curve easily once you get the corresponding values from part (a)

c) E=/

else from graph, E is the slope of the curve

d) proportional limit is the value of stress and strain till the point they vary linearly.

e) mark the point corresponding to 0.2% strain, then draw a line with slope =E, the point where this line intersects the original stres strain curve gives the yield stress.

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