ELMT13.C - - Linear Viscoelasticity Example

The elmt[01-50].f files in the user directory allow one to create user elements that will be added to FEAP's element library. To set up a user element one needs to edit the file elmt13.f (for example) to include the code one wishes to have executed when the user element is specified in the input file. The interface can be programed in FORTRAN or it can be programed in C. In the example that follows a C interface is utilzed to program a Q4 displacement element with a linear viscoelastic material model. Due to the differences in array storage methods (row major for C and column major for FORTRAN) one needs to be extra careful in interfacing C routines with FEAP's FORTRAN routines.

The main steps in creating a user element whether in C or Fortran are

Edit the elmt[01-50].[f,c] file and add the code to compute the required quantities. In particular one needs to add code to perform different task depending upon the 'isw' switch parameter that FEAP sets when calling the element; see the programmers manual for a description of the different tasks. The essential cases are:

isw = 0 Output descriptive name

isw = 1 Read input material data

isw = 2 Check mesh numbering order

isw = 3 Compute residual and tangent

isw = 4 Output stresses for printing

isw = 6 Compute residual