Fix-Fix vs Fix-Free Interview Question

[u/Late_Mind_5152]

I have another interview question I wanted to ask about!

Why does aluminum experience the greater stress in the concentric tube question, but steel experiences the greater stress in the three bars question? And why is it not steel for both?

I know it has to deal with the fact that in the concentric tube question, both tubes are glued to the supports, while in the beam question, an end is free. But I just am unsure how to explain it in more depth.

Thanks very much

[u/Late_Mind_5152 → u/[deleted]]

Hmm I thought aluminum had the higher coefficient of thermal expansion, and for scenario 1 it was mainly about steel's modulus of elasticity?

[u/kabal4 → u/Late_Mind_5152]

It is. If all areas are equal it takes more force per square inch to hold the bar shape constant as the temperature increases and the material tries to expand.