I've come across this phenomenon several times and never found any real reason for this.
When I consider a cylindrical object like a rod, I need to calculate several things. One of those is the stress tensor in cylindrical coordinates represented by $r$, $\theta$, and $z$ directions.
Now, in many books and in my lecture notes there's always this one line that says:
I know that when compressing a steel rod (assuming there is little to no friction at the contact points) the steel rod should get compressed in the $z$-direction and expand in the radial direction. Why is there no stress in the circumferential direction?
I've looked in many places and I hope that I didn't accidentally miss the other SE question with respect to this specific topic.