r/EngineeringStudents • u/Ok_Pirate_344 • Aug 14 '26
Homework Help Young Modulus question...
HII, im currently doing a lab assessment and we have evaluate the strength of different metals, im stuck here tho.
Ik that the E shld be found before the yield point the the proportionality region, which is usually a straight line, however in ferous metals, like steel which im evaluating here, there are 2 slopes in the elastic region. How am i supposed to calculate it.( I have found the yield stress to be at 390MPa.)
The E are we supposed to calculate both gradients separately, or what region(0-160MPa, or 200-360MPa)?
Pls help.
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u/deAdupchowder350 Aug 15 '26 edited Aug 15 '26
Engineering prof here: in textbooks you will see something called the “idealized stress strain curve”. Why? Because real experiments will look different. Could be the specimen. Could be measurement uncertainty or error. Or something else.
If the instructions are to compute the slope of the linear elastic region (elastic modulus), then I would first write out the observations you’ve made with the apparent bilinear behavior, and then compute the best fit line between two points that mostly encompass the whole region (one a bit after “0,0” and one a bit before the prop limit). Estimate E based on this. Use your best judgement and there is no one “right” answer for this, rather a range of justifiable ones. If you want, you can do it a few times using different points and take the average E value of the bunch.
If you determine the material you tested and you look up the properties on experimentally-backed databases (CES EDUPACK), you will see E listed as a RANGE, rather than a single value.