Reshaping the testing pyramid: Utilisation of data-rich NDT techniques as a means to develop a 'high fidelity' component and sub-structure testing methodology for composites

A key issue in the certification of composite structures is the heavy reliance on ‘coupon level’ tests that do not always translate well to the sub-structure, component and full scale structural behaviour within a ‘building block’ or ‘testing pyramid’ framework. This has a strong bearing on the certification process as many of the design allowables and failure predictions are determined from the behaviour of coupon specimens. The overarching aim of this work is to develop an understanding into the behaviour of composites at the larger sub-component scales, which better represent the in-service behaviour of these structures, reducing the reliance on extensive coupon level testing. This requires non-destructive testing (NDT) methods that are scalable to large components. This study investigates the feasibilities of Thermoelastic Stress Analysis (TSA) and Digital Image Correlation (DIC) as scalable strain based NDT methods that provide full-field information to study the effects of defects on structural composite components. Both techniques are successfully demonstrated showing their capability for detecting the detrimental effects of fibre waviness (wrinkles) on a thick non-generic composite component. X-ray computed tomography (CT) is used to validate the observations made with the two strain based NDT techniques.