The aim of this study is to analyze a mathematical model describing the contact between a deformable body and an obstacle. The material behavior is governed by a linear viscoelastic Kelvin-Voigt constitutive law involving time-fractional derivatives. The contact model combines normal compliance with unilateral stress constraints under Coulomb's friction law. We first derive the variational formulation and prove existence of weak solutions. Furthermore, we analyze a penalized version of the problem without constraints, demonstrating that its solutions converge to the original variational inequality solution as the penalty parameter tends to zero.
Cen et al. (Mon,) studied this question.