The FrD2 friction model is a second-order dynamic bristle model based on a shifted friction characteristic that targets long-term stiction and reproducible friction behavior. This paper shows that, contrary to earlier assumptions, in specific operation scenarios the FrD2 model can generate drift of the contacting bodies while the contact remains in the stiction regime. The drift is traced to asymmetrical excitation and the curved regularization of the friction characteristic, which introduces an operating-point-dependent local slope and thereby yields state-dependent effective stiffness and damping in the system dynamics. As a mitigation, a linearly regularized variant is proposed that suppresses this drift mechanism. In addition, a mechanism is discussed for both model variants, which can trigger premature sliding and leave a persistent displacement. It originates from dynamic overshoot near the static friction limit by bounding the shift of the friction characteristic. The findings are supported by linearization-based limit analysis and time-domain simulations.
Hanft et al. (Thu,) studied this question.