Explicit Finite Element Modelling as a Development Tool for New Ultrasound Testing Methodologies for Detection and Characterization of Porosity and Defects in Composites

Composite components frequently contain porosity or defects, which might, in some circumstances, be deemed benign. Other defects could lead to progressive or sudden failure in service, hence reliable and accurate material condition monitoring and health assessment is an important prerequisite for further design for the use of composite materials in high duty and life sensitive engineering components. The objective of this paper is to demonstrate the use of explicit finite element as an effective development tool in the development of ultrasound testing methodologies for the characterization of porosity in composites – a virtual ultrasound vibration laboratory. This would enable an improved inspection sentencing capability for as-manufactured composite structural components. It would also be of benefit in sentencing components subject to foreign object damage (FOD), in order to determine whether the component can continue in service, possibly with in-service monitoring or cosmetic repair, or must be condemned. In this work, finite element models simulating damage and porosity are presented. The models are compared with ultrasound tests on real specimens with practically relevant defects. Experimental tests, making use of wave superposition from two piezo-electric vibration sources, are shown to detect energy absorbing damage in the specimen, such as might have been created by impact or crush loads. The same piezo-electric vibration system is also used to measure the dissipated energy. Computational analysis, using simple material model variations, is able to replicate the Lamb wave generation and evolve a wave form resembling a “standing wave”. The computational material model is modified to represent porosity in composites