Ply-ply friction for UD C/PAEK tapes in melt under varying sliding rates

High fidelity composite forming simulations require accurate characterization and modeling of ply-ply friction. Most of the efforts so far considered constant sliding rates, yet these rates will certainly vary during actual forming processes. In this paper, we follow up on our previous research on ply-ply friction with novel varying-rate experiments using a newly developed friction tester. These experiments demonstrated that the peak friction depends on the sliding history for medium to high sliding rates, while this peak friction remains unaffected in the case of initial sliding with low rates. Further, a low-rate ramp mitigates a peak friction. These observations substantiate the concept of wall slip in the fiber–matrix interphase as the key underlying mechanism for the transient friction response, in line with our earlier work. Moreover, we discussed an extension to our earlier transient shear flow model that correctly describes the observed varying-rate friction, contributing to implementation in forming simulations. • Varying sliding-rate friction experiments were performed on UD C/PAEK tapes. • The sliding history affects the transient ply-ply friction response. • A low-rate ramp instead of a stepwise applied rate mitigates a peak friction. • A proposed model extension correctly describes the measured varying-rate friction.