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4.15.2.2 in-situ stretch
The in-situ stretch generator option calculates a prestrain gradient based on a fiber stretch and the fiber vector defined by the elastic material of the prestrain material. This implies that this elastic material must define a fiber property.
| parameter | description | initial values |
| stretch | initial fiber stretch | 1.0 |
| isochoric | use the isochoric prestrain generator option | 1 |
This option generates one of the following prestrain gradients, depending on the isochoric option.
If the isochoric option is set to 1, then is used. Otherwise, is used.
The rotation tensor is defined implicitly via the fiber vector and the prestrain gradient tensor is effectively determined via,
where the prescribed fiber stretch, and or depending on the isochoric option.
Example:
<material id="1" type="prestrain elastic">
<elastic type="coupled trans-iso Mooney-Rivlin">
<k>0.1</k>
<density>1e-09</density>
<c1>0.01</c1>
<c2>0</c2>
<c3>0.0139</c3>
<c4>116.22</c4>
<c5>535.09</c5>
<lam_max>1.046</lam_max>
<fiber type="vector">-0.0804,-0.508,-0.858</fiber>
</elastic>
<prestrain type="in-situ stretch">
<stretch lc="1">1.05</stretch>
<isochoric>1</isochoric>
</prestrain>
</material>