Understanding the Origins of Defects and Variability in Composites Manufacture

As the volume of advanced composites components for aircraft applications continues to rise and primary structures are increasingly made from advanced composites it is necessary to review the quality of the materials, processes and design practices that are used to generate those composite structures. As production rates are expected to expand very markedly the quality target must be zero defects, zero rework and repair (with the associated concessions), and zero scrap. This paper reviews the sources of variability and defects in aircraft composite parts, and attempts to identify approaches that can be taken to generate more robust design and manufacturing processes. More than 130 defect types and more than 60 sources of variability and unreliability can be identified for the autoclave and resin transfer moulding processes. Many of these sources of variability have their roots in the reinforcements used and in the ways that those reinforcements map to the geometry of components. Almost all of our mechanical property data is generated from flat laminates, but almost all useful components are of more complex geometry. Understanding the underlying variability of reinforcements and their deformation and consolidation characteristics is one key to the understanding of variability in product performance.