We present for the first time an approach for identifying the geometric and material characteristics of layered composite structures through an inverse wave and finite element approach. More specifically, this Non-Destructive Evaluation (NDE) approach is able to recover the thickness, density, as well as all independent mechanical characteristics such as the tensile and shear moduli for each layer of the composite structure under investigation. This is achieved through multi-frequency single shot measurements. It is emphasized that the success of the approach is independent of the employed excitation frequency regime, meaning that both structural dynamics and ultrasound frequency spectra can be employed. It is demonstrated that more efficient convergence of the identification process is attained closer to the bending-to-shear transition range of the layered structure. Since a full FE description is employed for the periodic composite, the presented approach is able to account for structures of arbitrary complexity. The procedure is applied to a sandwich panel with composite facesheets and results are compared with two wave-based characterization techniques: the Inhomogeneous Wave Correlation method and the Transition Frequency Characterization method.Numerical simulations and experimental results are presented to verify the robustness of the proposed method.

There exists a great variety of structural failure modes which must be frequently inspected to ensure continuous structural integrity of composite structures. This work presents a finite element (FE) based method for calculating wave interaction with damage within structures of arbitrary layering and geometric complexity. The principal novelty is the investigation of pre-stress effect on wave propagation and scattering in layered structures. A wave finite element (WFE) method, which combines FE analysis with periodic structure theory (PST), is used to predict the wave propagation properties along periodic waveguides of the structural system. This is then coupled to the full FE model of a coupling joint within which structural damage is modelled, in order to quantify wave interaction coefficients through the joint. Pre-stress impact is quantified by comparison of results under pressurised and non-pressurised scenarios. The results show that including these pressurisation effects in calculations is essential. This is of specific relevance to aircraft structures being intensely pressurised while on air. Numerical case studies are exhibited for different forms of damage type. The exhibited results are validated against available analytical and experimental results.

Previous studies on wave inspection in different propagation directions have focussed on the analysis of wave propagation and wave scattering from various types of joints in two-dimensional monolayered structures. In this work, a Finite Element (FE) based numerical scheme is presented for quantifying wave interaction with localised structural damage within two-dimensional layered composite structures having arbitrary layering, complexities and material characteristics. The scheme discretise a damaged structural medium into a system of N healthy substructures (waveguides) connected through a joint which bears the localised structural damage/discontinuity. Wave propagation constants along different propagation directions of the substructures are sought by combining Periodic Structure Theory (PST) and the FE method. The damaged joint is modelled using standard FE approach, ensuring joint-substructures mesh conformity. This is coupled to the obtained wave propagation constants in order to determine scattering coefficients for the wave interaction with damage in different propagation directions within the structure. Wave interaction coefficients for different damage types and structural parameters are analysed in order to establish an optimum basis for detecting and identifying damage, as well as assessing the orientation and extent of the detected damage. The main advantage of this scheme is precise predictions at a very low computational cost.

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The increased use of composite materials in modern aerospace and automotive structures, and the broad range of launch vehicles' operating temperature imply a great temperature range for which the structures has to be frequently and thoroughly inspected.