Grid Point Stresses

The default method of calculating stresses in OptiStruct produces values of stress components at the centroids of elements.

Typically a post-processor, such as HyperView, will then average these values to produce smooth contour plots. This method, while useful for viewing stress distribution, may underestimate stress maxima, especially on the surface of the body.

To provide higher accuracy stresses, OptiStruct supports grid point stress calculation. Grid point stresses are computed using the following steps:
  1. Calculate stress components at integration points of elements (these are generally the most accurate stress locations).
  2. Extrapolate stress values to element nodes (grid points).
  3. Calculate average at each grid point using values from surrounding elements.
  4. Calculate derived quantities, such as von Mises stress or principal stresses, at each grid point (this assures that these values are consistent and make physical sense).

The above approach produces continuous stress field, typically in the entire domain. Since, however, stresses can be discontinuous between different materials, OptiStruct supports calculation of separate grid point stress field per each material sub domain. The presence of more than one material is detected automatically and then grid point stresses are calculated for the entire domain and as a separate field for each material region.

Grid point stress calculation is activated through the I/O Subcase command GPSTRESS. When activated, grid point stresses are produced in addition to default stress results - they can be found in a separate results subcase.

The present support for grid point stress capability has the following scope:
  • It is supported for nodes connected to three-dimensional solid elements
  • It is available for static load cases and non-design elements
  • Grid point stresses are always calculated in the basic coordinate system