8 - Case studies: failures due to overload and design deficiencies

Abstract

To demonstrate how fractographic analysis can be used to deduce information on the failure of composite components, the mechanisms of failures due to overload and design defi ciencies are considered. Case studies, drawn from both laboratory and in-service investigations, demonstrate the methodologies and use the morphologies described elsewhere in the book. These failures cannot be attributed to a particular defect, but show that the component has been exposed to excessive loading (overload) or that the loading has been such that the local stress concentrations at geometric features have acted as failure initiation sites. The first two failure examples are attributed to overload and are of a military aircraft component and a tragic accident of a civil airliner. Examples of design defi ciencies are presented; partitioned into in-plane (notched shear web) and delamination (stiffener runout) to demonstrate the respective failure modes, whilst the third case study (generic nacelle element) demonstrates a combination of these modes. The fi nal two case studies demonstrate failure in spar/skin or stiffener/skin structures, but in two very different composite materials.