Numerical and Experimental Investigation of Prepreg Compaction for Defect Formation Mechanisms

Abstract

Manufacturing defects in composites materials are responsible for severe reduction in mechanical properties. For example, it is reported in the literature that out-of-plane waviness can cause up to 36% knockdown on the overall strength of composites parts. The formation of fibre wrinkling is influenced by through-thickness compression and shear forces during processing and is one of the more detrimental defects that can be found in composites materials. In the present study an experimental and numerical programme is undertaken to explore the compaction behaviour of carbon fibre prepreg material under processing conditions consistent with automatic fibre deposition, hot debulking and pre-cure consolidation in an autoclave. Two main concurrent deformation mechanisms were observed in a bespoke experimental programme; shear flow, where the laminate behaves as a highly viscous incompressible fluid, and percolation flow where the pressure gradient causes resin flow relative to the fibres. An analytical model, based on micro-structural considerations and addressing the percolation/shear flow transition, was developed. A 3D hyper-viscoelastic constitutive relation was then constructed based on this analytical model and implemented in implicit formulation within the finite element package Abaqus/Standard. The model was validated against compaction experiments over a wide range of load rates, temperatures, and laminate configurations