Shear mechanism modelling of heavy tow braided composites using a meso-mechanical damage model

Heavy tow braid reinforced composites are a potential substitute for metals in automotive and other transport applications. These composites, if properly designed, can provide lightweight efficient load bearing structural members that can also absorb high specific energy under impact and crash loading. Many of these components are ‘beam like’ members that must resist large transverse deformations at high force levels, thereby absorbing high levels of energy. This class of composite component is particularly considered in this paper.An effective means to achieve high energy absorption is careful design of the fabric architecture so that shearing mechanisms of the fibre/matrix interface, without premature fibre failure, are possible. Characterisation and modelling of progressive shear damage and failure occurring in biaxial carbon and glass braided composites are investigated. Fibre re-orientation and fibre/matrix interface damage is measured using an optical strain measuring method based on digital image correlation (DIC). This is then used to provide input to a meso-mechanical damage model in an explicit finite element code. A modelling approach using coupled layers of equivalent unidirectional plies is used to represent the biaxial braid composite and validation of the approach has been performed against test coupons and beam structures loaded transversally to failure.