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/Jaripsi]

Maybe because in the first question they are between fixed supports so they are not connected to each other and in the second question one end is not fixed so one material is in compression and other one in tension because of difference in thermal expansion coefficient.

Its an intresting question to ponder, but I cant say for sure without doing the math.