Extreme shearography

Abstract

Monitoring of extreme dynamic loadings on composite materials with high temporal and spatial resolution provides an important insight into the understanding of the material behaviour. Quantitative measurement of the surface strain at the first moments of the impact event may reveal the initiation of the failure mechanisms leading to damage. For this purpose, we developed a shearography instrument for strain measurements during a severe impact event at µs temporal resolution. This paper presents the design, development and experimental measurement of the surface strain during an impact on aluminium and composite samples. The final design realises measurements of the in- and out-of-plane surface strain components to improve coupling of experimental data with the numerical models. The experiments on aluminium and composite specimens revealed the main elastic material response to be in the first 1-2 µs after the impact followed by the initiation and propagation of flexural waves causing in- and out-of-plane deformation. Further analysis of the wavefronts will be used as input and validation data for new numerical and analytical models of the impact response of composites and for validation of other experimental techniques as acoustic emission and embedded piezo sensors. The set of technical parameters of the developed shearography instrument makes it one of the most extreme applications of shearography for material characterisation. The framework for this work is the “EXTREME Dynamic Loading – Pushing the Boundaries of Aerospace Composite Material Structures” Horizon 2020 project.