Hello everyone,

In Abaqus, my model uses shell elements. After the simulation when I try to compare the principal stresses, there are 4 possibilities :

1. Max In-plane Principal

2. Max Principal

3. Min In-plane Principal

4. Min Principal

I was expecting 1. and 2. to produce the same values. Same goes with 3. and 4.

However, the in-plane principal stresses and the principal stresses are producing different values. (See attached pictures)

Could someone shed some light on this? Would be very helpful to me!

(The simulation is a thin-walled pressure vessel made of rubber, under 0.5 MPa internal pressure loading.)