Novel Strain-based NDE for Online Inspection and Prognostics of Composite Sub-structures with Manufacturing Induced Defects

To save time and reduce wastage it is essential that an inspection technology is developed that can be used to intervene at the manufacturing stage and provide high fidelity data for model based prognostic capability (beyond simply sizing defects) to further inform the decision process of ‘accept’, ‘rework’, ‘repair’ or ‘scrap’. To this end a novel inspection procedure for cured composite components was developed, which has the ability to provide high fidelity local strain/stress data to inform model-based prognostics and define how a given defect will evolve under service load. The novelty is based on the ability to simultaneously measuring the strain and a stress measure or metric in the vicinity of a manufacturing defect or intrinsic subsurface artefact incl. variability of fibre volume fraction and fibre orientation, wrinkles, etc, and not just the geometry and size.

To apply the fundamental conceptual idea successfully significant innovation is required to mimic the service loading mode on high value manufactured components, e.g. aerospace components, so the strain/stress distribution in the neighbourhood of the defect is representative. Knowing the strain/stress distribution gives additional information and inputs to models and, along with the component material properties, enables a prognosis on if and how the defect would grow.

To understand the mechanisms contributing to material heterogeneity in high volume manufactured parts, a study of discontinuous compression moulded composite materials was conducted. Surface strains and stresses have been extracted and X-ray CT has been used to quantify volumetric variability in local resin volume content and distribution of local fibre orientations. A novel approach has been demonstrated that allows (very) rapid and potential in-situ manufacturing inspection of parts based on vibration based loading with the potential to link the complex response from the material surface to be linked to the manufacturing procedure.