Learning Forum

[peteroznewman]

nStress is computed in each element at the integration points, then extrapolated out the the nodes of the element. If a node is connected to 8 solid hex elements, that node has 8 values of stress. If a node is connected to 4 shell quad elements, that node has 4 values of stress. You can plot the averaged value of stress at each node and the contour shows smooth transition of stress from one element to the next. Or you can plot the unaverage stress on each element. The unaveraged plot has stress values that make step changes at element boundaries. If the stress is changing slowly and the elements are small, the step is small. If the stress is changing rapidly and the elements are large, the step is large. A large step shows that the elements are not small enough to capture the stress gradient accurately. That is why you can plot the size of the step directly using Nodal Difference, to identify areas to improve the mesh.nAn example is an aluminum deposition coating a glass part to make a mirror. When the temperature changes, stress is caused by the different coefficients of thermal expansion. The stress in each material is computed by the elements. There is a layer of nodes at the interface that have a glass element on one side and an aluminum element on the other side. That node has multiple values of stress that you don't want to average across the bodies (but you do want to average within a body). One layer deeper into the mesh, there is a layer of nodes that have the same material on each side. That node also has multiple values of stress, but you do want to average those.nI think you have another discussion to talk about sudden geometric change, so let's discuss that in the other thread.n