Extraneous Stiffness Parameters

Insert the extraneous stiffness parameters required for reduced integration elements with user materials.

Helius PFA uses a *User Material definition instead of a *Elastic definition to define a material in Abaqus. When a *User Material definition is used, Abaqus is unable to compute certain section parameters because the elastic constants necessary to compute these section parameters are not available. You must define these parameters for an analysis to run successfully.

Helius PFA comes with a command line program called xStiff that reads an Abaqus input file and automatically computes and inserts the extraneous stiffness parameters required by reduced integration elements that utilize Helius PFA materials. This auxiliary program significantly improves the speed and accuracy of the model building process.

Typically, xStiff is executed after the model is built and before the model is submitted for analysis. Here, the input file for this analysis will be written and xStiff will be used to calculate and insert the appropriate extraneous stiffness parameters.

1. Open the Helius PFA 2016 Command Shell and change the directory to the location of the Tutorial_5.inp file.

   >>cd <directory containing input file>

2. In the Command Shell, enter:

   >>xstf -i Tutorial_5

3. xStiff will write a modified input file and rename it Tutorial_5_xs.inp.
4. Open the new file and note the addition of the extraneous stiffness parameters to the section definition. In particular, xStiff added the following section parameters:
   • Poisson
   • Thickness Modulus
   • Transverse Shear Stiffness
   • Hourglass Stiffness