UCONST.F - - Cubic St.Venant Example

The uconst.f file in the user directory allows one to create user constitutions that will be added to FEAP's material library for use with FEAP's internal elements. To set up a user constitution one needs to edit the file uconst.f to include the code for reading input data for the new model; this will be stored in the ud(*) array and kept separate from FEAP's own material data array d(*). The other routine to be edited is the umodel.f file which will be called when the stresses etc. need to be computed for residual and tangent operations etc. What is shown below is a rather elementary implementation that does not get to fancy.

The main steps in creating a user constitution are:

Edit uconst.f to set the material identifier number umat which corresponds to the user model type requested in the input file.
Edit uconst.f so that it reads in the user data and passes it out in ud(*) and additionally in n1 and n3 set the required history amounts per gauss point.
Edit umodel.f so that it responds to the following isw switches

isw = 3 Compute stressess and material tangent
isw = 4 Compute stresses for output
isw = 6 Compute stresses for use in residual calculations
isw = 8 Compute stresses for use in plotting

To use the model one needs to compile the following routines. A sample call to these routines would look something as follows

mate

solid
finite
ucon,cubic
alpha,1.0
beta,2.0
gamma,3.0
aaxis,1,1,1
baxis,1,-1,0
ucon,end

In this alpha, beta, and gamma are the 3 cubic constants and aaxis and baxis denote the direction of two of the principal cubic axes in the coordinate frame used to define the mesh. They need not be unit length but they must be orthogonal. The program automatically computes the third principal cubic axis internally. If you wish to run the model in the small deformation setting use:

mate

solid
small
ucon,cubiclin
alpha,1.0
beta,2.0
gamma,3.0
aaxis,1,1,1
baxis,1,-1,0
ucon,end

Source files: Dowloading versions

Description of the consitutive equation