A state-rate model for the transient wall slip effects in ply-ply friction of UD C/PAEK tapes in melt

Ply-ply slippage is one of the key deformation mechanisms occurring during hot press-forming of thermoplastic composite laminates. Advanced forming simulations, required for defect-free manufacturing, rely on accurate constitutive models for these deformation mechanisms. In this work, we propose a relative simple, yet accurate, transient model to describe the start-up friction response of UD C/PAEK tapes. The model combines a White–Metzner viscoelastic fluid with a state-rate model for the evolution of wall slip near the fiber–matrix interface, describing the disentanglement of surface polymer chains followed by the settlement of these chains in a new equilibrium state. This allows prediction of the stress growth at start-up and the transition from peak to steady-state friction, from smooth to sharp with increasing sliding rate, as well as the magnitude of the peak and steady-state friction. We obtained a good correlation between the modeled and measured friction response for different sliding rates.