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The optimization calculates an approximated von Mises stress and shows these values in the postprocessing.
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The elected stress goal is the overall optimization goal for the optimization and has a big influence on the resulting design. The target is that the material of the part is evenly loaded and the stress uniformly distributed. Thus, the stress goal isn’t the maximum stress which can occur at design space limits or due to FE singularities, but the value which is a good middle value for a long part life (green areas in the example above). Not in every case the yield strength of the material is the best value for this parameter, e.g. when the applied loads are too small to result in such stresses. By changing the stress goal, the stiffness of the structure can be influenced as well. Due to uniformly distributed stresses, lower stress goals result in stiffer parts at the most lightweight design.
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For each resolution level a different stress percent goal is defined which is dependent on the stress goal set for the optimization. On the lower resolution levels the stress goal varies on purpose from the requested stress goal to realize a fast material reduction and therefore design generation. On the highest resolution level, the requested stress goal reaches 100% and thus satisfies the defined stress goal as the geometry allows it.
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In one optimization several Events (load cases) can be considered. Each Event is calculated by itself and the stresses of all Events are enveloped and the highest stress for each area is considered. For information regarding event specific stress constraints have a look here.
The stress calculation is from an FE point of view an estimation. That’s why we recommend a FE reanalysis using Apex Structures/Nastran to verify the results regarding all boundary conditions. For the reanalysis the intersected model should be used which will be manufactured and used. The reanalysis can also take dynamic loading & other boundary conditions into consideration that are not considered in the design process. For more information regarding intersection have a look here.
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