  We formulate a quasistatic nonlinear model for nonsimple viscoelastic
materials at a finite-strain setting in the Kelvin's-Voigt's rheology where the
viscosity stress tensor complies with the principle of time-continuous
frame-indifference. We identify weak solutions in the nonlinear framework as
limits of time-incremental problems for vanishing time increment. Moreover, we
show that linearization around the identity leads to the standard system for
linearized viscoelasticity and that solutions of the nonlinear system converge
in a suitable sense to solutions of the linear one. The same property holds for
time-discrete approximations and we provide a corresponding commutativity
result. Our main tools are the theory of gradient flows in metric spaces and
Gamma-convergence.
