= Multiplicative decomposition of the deformation gradient
{title2=$F=F_*A$}
The factor $A$ can encode an internal relaxed configuration, while $F_*=FA^{-1}$ determines the instantaneous elastic energy. Differentiating $F_*$ at fixed $F$ or fixed $A$ produces the corresponding <nominal stress tensor> and <thermodynamic force conjugate to an internal variable>. This is a kinematic decomposition, not an assertion that each factor separately derives from a global <deformation map>.
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