In FEA simulation of simple beams (3D solid and shell/plate), I have taken a simple geometry:
- A long beam in the y direction
- a concentrated load applied on the plane of symmetry
There is a pin or roller joint at some point between the symmetry plane and end of the beam:
load a b c↓ ======================⌇ y-symmetry ▲ free pin
In this system, when we solve with the typical beam equation, we assume that the angle of deflection is small. In that case, we see a slight axial distortion between the pin and free end because the total deflection is very small.
However, when we solve this with 3D FEA elements, I would expect the length of the beam from a-b to be conserved. In my understanding, I expect the the shear and moment on elements beyond the joint to be zero. However, in practice I have seen beams with finite-thickness-shell elements and 1 and 2 element thick solid plate (cannot go thicker because of software limitations) meshes result in extreme axial distortions of this region when the load is large.
Is the mesh distortion here unphysical? What is the cause of this behavior? What are some ways to reduce or eliminate this behavior?
Should I simply not include this region in a simulation? If so, what are some guidelines or considerations for deciding what regions to expect such behavior in order to eliminate/reduce it?