(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

Determine

a)where the greatest stresses are

b) overall change in length

That is meant to be a hollow cylinder on the bottom section inbetween the dotted lines

E = 200 GPa

2. Relevant equations

σ = Fn / A

ε = dl / lo = σ / E

3. The attempt at a solution

The book gives the answer as the top of the rod having the greatest stress = 7.64 MPa

So working back from that answer the force on the top of the rod = 15 kN

I assumed this was because -20+10-5 = -15 kN, but when I used -15 kN for the rest of the sections the stress was much higher due to the smaller area.

ie. 15e3/[(pi 25 mm^2)] = 7.64 MPa (top section)

15e3/[(pi 20 mm^2)] = 11.94 MPa (middle section)

15e3/ [(pi 10mm^2)] = 47.75 MPa (bottom section)

So my problem is that I don't know whether to include all the forces when calculating strain for each section or not..

Thanks

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# Homework Help: Mechanics - stress on rod of differing thickness and change in length

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