“…Condition (1.2) is quite difficult to handle analytically due to the fact that it is not compatible with some common hypotheses (e.g., monotonicity with respect to the strain rate) on the stress (see [12], [29,Section 2.3]). The existence of a dissipation potential R means that there exists a real-valued function R(x, F,Ḟ ) with R(x, F,Ḟ ) ≥ R(x, F, 0) = 0 such that ∂Ḟ R(x, F,Ḟ ) = S(x, F,Ḟ ).…”