Calculate Stress & Strain from Length, Diameter & Load

[Chuck Finley]

Unsure how to calculate in order to get the stress (N/mm2) and strain (%) if:
a material has a length of 50mm
diameter of 12mm
Load: 11.5 kN
Extension 0.025 mm

Help on how to work this out would be very appreciated :)

 

[jambaugh]

Note the forum guidelines insist you show some attempt but let me see if I can get you started.

You need the mental picture of, I think in this case, tensile stress and strain. It appears as if the material is cylinderical so has a circular cross sectional area. Note that the stress units are force per area. Double check your textbook on the definition of stress. [If you haven't a clear idea of its definition you should not have started this problem yet.]

Secondly the cylinder has a length (50mm) and that is extended by the strain produced by the force (the extension amount) and so % strain should be an obvious calculation. Note that tensile stress extends along the entire length of a wire or rod so doubling the rod is equivalent to stacking two rods so doubling the length should double the strain for the same material and stress. Strain is proportional to the length in other words so it makes sense to express it as a proportion change.
[Again this is something you should understand before attempting the specific problem.]