I have values of stress in Gauss points I would like to crea

I have values of stress in Gauss points. I would like to create a stress contour plot. How can I know values of stress in other points? Do I have to care about shape functions?

Solution

The stresses at the integration points are the most accurate. They occur inside the element and may not be the highest stress in the area; for example around a fillet radius the free surface stress will be higher than the integration point stress.

The element shape function is used to extrapolate the integration point stresses out to the element nodes - these are in a useful location like a fillet radius free surface or a hole edge.

Adjacent elements combined with their shape functions will predict different stress values at their common nodes. The question then arises which stress do you believe? Most FE packages average the stresses for each element at the node.

If the unaveraged stresses are within a few percent of each other I go ahead and use averaged nodal stresses. If the unaveraged stresses are significantly different, I use peak unaveraged stresses, or refine the mesh to get a better result.

IN ALL CASES, UNAVERAGED NODAL STRESSES MUST BE CHECKED BEFORE USING AVERAGED NODAL STRESSES.

WHEN USING SHELL, BEAM, OR ANY OTHER ELEMENT FOR WHICH RESULTS ARE PRESENTED IN SOME FORM OF LOCAL SYSTEM, AVERAGED NODAL STRESSES SHOULD NOT BE USED UNLESS YOU REALLY KNOW WHAT YOU ARE DOING.