Damage and Failure of Non-Conventional Composite Laminates

Abstract

For a long time, the application of composite materials was restricted to military aircraft and secondary structures of commercial aircraft. Furthermore, the design possibilities offered by composite laminates were narrowed to quasi-isotropic configurations due to their closer behaviour with monolithic materials, hence with a more predictable response, and easiness of manufacturing. However, this picture is changing. Nowadays, there are automated systems capable of rapidly manufacturing large and high quality composite parts. As an example, the fuselage of the all-new long haul Boeing 787 aircraft is being built by means of automated fibre-placement machines. These highly precise systems can build laminates made of combinations of ply angles other than the conventional 0 degrees, 90 degrees and 45 degrees. Furthermore, automated fibre-placement machines can steer the fibres tows as these are being placed, resulting in plies with variable fibre orientation and laminates whose elastic properties vary along their planar coordinates, termed “variable-stiffness panels”. In this thesis, the expression “non-conventional composite laminates” refers to straight-fibre laminates made of combinations of non-conventional ply angles as well as to variable-stiffness panels. The structural behaviour of these non-conventional composites is not fully understood yet, particularly their damage and failure responses. The goal of this thesis is to shed light on this field.