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4.4.1 Uncoupled Viscoelastic Materials
These materials produce a viscoelastic response only for the deviatoric stress response. They must be used whenever the elastic response is uncoupled, as in the materials described in Section 4.1.2↑.
The material type for these materials is “uncoupled viscoelastic”. The following parameters need to be defined:
|<g0>||viscoelastic coefficient||1||[ ]|
|<g1>-<g6>||viscoelastic coefficients||0||[ ]|
|<elastic>||elastic component (must be an uncoupled elastic solid)|
For a uncoupled viscoelastic material, the second Piola Kirchhoff stress can be written as follows : where is the elastic stress derived from (see Section 4.1.2↑) and is the relaxation function. It is assumed that the relaxation function is given by the following discrete relaxation spectrum: Note that the user does not have to enter all the and coefficients. Instead, only the values that are used need to be entered. So, if is 2, only , , and have to be entered.
The elastic parameter describes the elastic material as given in Section 4.1.2↑.
<material id="1" name="Material 1" type="uncoupled viscoelastic"> <g1>0.95</g1> <t1>0.01</t1> <k>100</k> <elastic type="Mooney-Rivlin"> <c1>1</c1> <c2>0.0</c2> </elastic> </material>