Process modelling for distortions in manufacturing fiber reinforced composite materials

Abstract

A fibre reinforced composite part generally takes a shape different from the one that is originally designed after removing from the mould at the end of the curing process. Due to the anisotropic nature of the fibre reinforced composite materials, the Coefficient Of Thermal Expansion (CTE), the cure shrinkage rate and the stiffness are direction dependent. The direction dependent behaviour of the composite materials, with the aid of temperature change during curing, triggers some mechanisms that are responsible for the residual stresses and shape distortions. Composite parts of various geometries (L-section, U-section and flat strip laminates), various stacking sequences, thicknesses and lay-up conditions are manufactured by using prepreg material system designated as AS4/8552. These parts were scanned using a 3D laser coordinate scanner to obtain the distorted geometry. A 2D and 3D Finite Element model has been developed for predicting shape distortions during curing of fibre reinforced composite parts. The total curing process is divided into three steps that corresponds the states that resin is passing through during curing: viscous, rubbery, and glassy. The material property changes during curing are implemented in the model through a three step user subroutine. Various mechanisms that contribute to shape distortions are identified and their relative contributions are assessed. Some observations on final shape and manufacturing defects are addressed. The shape distortion predictions are compared to the distortions measured by 3D laser coordinate scanner and satisfactory results are obtained.