Friction Resistance of Uncured Carbon/Epoxy Prepregs under Thermoforming Process Conditions: Experiments and Modelling

Abstract

The numerous prepreg characteristics benefit industries like the aerospace and automotive ones, producing a wide range of high-performance components for primary or secondary applications. Parts production is usually assisted by a thermoforming process in which the prepreg is heated and reshaped employing a moulding system. The ply-ply and ply-tool sliding behaviours in the Thermoforming govern the defects generation, such as wrinkles, making its study a crucial step. This work analyses ply-ply and ply-tool friction coefficients for UD AS4/8552 Carbon/Epoxy prepreg. A pull-out test method was employed to determine the friction coefficients at different velocities, pressures, and temperatures related to the thermoforming process conditions, supplying a detalied report of friction parameters and mechanisms. The measurements of the interlaminar resin layer thickness and the surface roughness geometry resulted respectively in a range of 11–14 μm and 3–4 μm were taken into account in the Lubrication Theory approach to developing an analytical model. Based on the Stribeck curve and Reynolds equation for a viscous fluid, the developed model accurately predicts friction coefficients for prepreg composite materials in the process and contact conditions mentioned below.