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 and I want to deform it in any way, I need to calculate several things, one of those things is the stress tensor. Mind you that I'm talking about a cylindrical coordinate system with $r,\theta$, and $z$ directions.

Now, in many books and in my lecture notes there's always this one line that says:

$$ \frac{\partial\bullet}{\partial\theta}=0$$

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. But I can't imagine why there is 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.

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:

$$ \frac{\partial\bullet}{\partial\theta}=0$$

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.

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 and I want to deform it in any way, I need to calculate several things, one of those things is the stress tensor. Mind you that I'm talking about a cylindrical coordinate system with $r,\theta$, and $z$ directions. Now, in many books and in my lecture notes there's always this one line that says:

$$ \frac{\partial\bullet}{\partial\theta}=0$$

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. But I can't imagine why there is 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.

Many thanks for any consideration and answer.

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 and I want to deform it in any way, I need to calculate several things, one of those things is the stress tensor. Mind you that I'm talking about a cylindrical coordinate system with $r,\theta$, and $z$ directions.

Now, in many books and in my lecture notes there's always this one line that says:

$$ \frac{\partial\bullet}{\partial\theta}=0$$

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. But I can't imagine why there is 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.