Variability, fibre waviness and misalignment in the determination of the properties of composite materials and structures

This paper will examine how the choices made in the design of components can influence the properties of composite materials. It will seek to demonstrate that features of the micro and meso-structure which are directly attributable to design decisions must be rigorously identified; and the influence of those features on composite properties must be explicitly included in determining allowable properties. We can then recategorise what we currently experience as defects into design induced defects, which might more properly be regarded as features, and process induced defects which are truly defect states that we can influence by correct choice of manufacturing conditions. Critically, it is necessary that true defect states and variability must be clearly distinguished from inherent or designed-in features as the latter cannot be eliminated by improvements in manufacturing processes. Design defects can only be avoided at the design stage.