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ALTAIR OptiStruct Interface

The strength assessment performed by the software LIMIT® incorporates a static and fatigue module to evaluate your structure. Base material as well as weld analysis can be accomplished using the commercial finite element code OptiStruct (Altair Engineering GmbH).

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Required import files for LIMIT

To allow a fatigue assessment of your structure using OptiStruct (Altair), you have to have the .fem to access the finite element model and the .op2 with all relevant result data.

Importing the .fem-file into LIMIT-CAE

  • Export model with standard format
  • Import .fem

Note: There might be issues concerning element sets and node sets exported by Hypermesh. If so do not export the sets to the model file.

Coordinate systems


  • Definition in the global coordinate system
  • Definition using CORD1R or CORD2R (RECTANGULAR)

Result data must exist in the global coordinate system (Solids) respectively in the default element coordinate system (shells).

Modifications for OP2-Output

  • sort: SORT1
  • Data format: REAL
  • Yield criteria: VONMISES
  • Position: BILIN (necessary for analyzing the gradient) or CORNER


Note: LIMIT® can average corner values of different elements, which is activated with the key *CENTER_STRESS

  • Geometry must be written to .op2-file:              PARAM, POST, -1


  • Please don‘t use:                                                    PARAM, PATVER, 2

Supported Altair OptiStruct Versions in Release Package

  • Altair OptiStruct 2020.1
  • Altair OptiStruct 2019

If you need a different version please contact our LIMIT® support.

Following elements can be analyzed


  • CTETRA (4 nodes) (not suitable for stress assessment)
  • CPENTA (6 nodes) (less suitable for stress assessment)
  • CHEXA (8 nodes) (less suitable for stress assessment)
  • CTETRA (10 nodes) => stress gradient available
  • CPENTA (15 nodes) => stress gradient available
  • CHEXA (20 nodes) => stress gradient available


  • CQUAD4
  • CQUAD8
  • CTRIA3
  • CTRIA6

For detailed information please refer to the OptiStruct interface document (.pdf) or contact our LIMIT® support.