This directory contains results from the axial traction test using a
generalized Maxwell viscoelastic material model. The test is a simple test
using a cube-shaped domain. All cube faces except the upper one (zmax) have
displacements constrained in the normal direction. A constant traction is
applied to the upper face. As a result, all horizontal strains are zero,
and the vertical stress is equal to the applied traction value. The
horizontal stresses are equal, and will vary with time according to the
selected set of parameters. Similarly, the vertical strain will also vary
with time. The current implementation of a generalized Maxwell model allows
up to 3 Maxwell models in parallel with a spring (which may have zero shear
modulus). The various problems consist of several different variations, with
the simplest example (1) being a single Maxell model (spring and dashpot in
series). For this case, there is a simple analytical solution, as described
by Turcotte & Schubert (1982).

For comparison, we have run the same problems using the finite element code
FEAPpv (http://www.ce.berkeley.edu/~rlt/feappv/), which uses a similar
implementation of the generalized Maxwell model. We have found that there
is a problem with properly initializing the viscous strain in this model
when going from the elastic solution to the time-dependent solution, which
could be a problem with the code, or could be due to using it incorrectly.
The simplest way to overcome this problem is to simply use smaller time
steps. These results are contained in the *s.res files. We have also
included PDF's showing a comparison of the horizontal stress over time.
