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Non-destructive testing (NDT) techniques are usually used for the characterisation of defects arising in polymer composites during manufacturing or in-service use. However, each of these NDT techniques cannot always allow a full diagnosis of the material's or component's structural health. Thus, several techniques have to be combined in order to improve the diagnosis of the damaged state of composite structures and their evolution during the part's life span. This opinion paper proposes a critical overview of the use and applicability of these NDT techniques for the detection and characterisation of damage to structural composite materials in view of in-service performance assessment and residual durability prognosis. It also addresses some current trends of structural health monitoring (SHM) of these materials, such as sensor–actuator embedding and NDT data fusion, and draws future perspectives on how composite SHM could evolve in the digital era, taking advantage of artificial intelligence, Internet of Things and big data to implement digital twins. [ABSTRACT FROM AUTHOR]

Polymer composite materials are being increasingly used in primary load-bearing structures in several advanced industrial fields such as aerospace vessels, railway wagons and mega-scaled wind turbines where detection of subcritical damage initiation can significantly reduce safety issues and maintenance costs. It is therefore crucial to inspect these composite structures in order to assess their structural health and to ensure their integrity. Non-destructive testing techniques (NDT) are used for this purpose, making it possible to monitor mechanical damage of composite materials under in situ or ex situ service conditions. This paper reviews the capabilities of the most common NDT techniques used to inspect the integrity of composite materials. Each technique has a detection potential and cannot allow a full diagnosis of the mechanical damage state of the material. Thus, depending on the occurring damage mechanism and the conditions of use, one technique will be preferred over another, or several techniques should be combined to improve the diagnosis of the damage state of the structures. [ABSTRACT FROM AUTHOR]

A method for simultaneous measurement of the thickness and density for Glass Fiber-Reinforced Polymer (GFRP) laminate plates with ultrasonic waves in C-Scan mode is presented in the form of maps. The method uses three different signals in immersion pulse-echo C-Scan mode. The maps obtained based on the density show the heterogeneity of the material at high resolution at the pixel level (1 × 1 mm 2 ) and therefore they represent an efficient tool to assess and evaluate the damage of the composite structures after manufacturing and after an applied mechanical loading. [ABSTRACT FROM AUTHOR]

Multi-objective parametric optimization problem is presented for overwrapped composite pressure vessels under internal pressure for storage and heating water. It is solved using the developed iterative optimization algorithm. Optimal values of design parameters for the vessel are obtained by varying the set of parameters for composite layers, such as the thickness of layers and radii of polar openings, which influence the distribution of fiber angles along the vessel. The suggested optimization methodology is based on the mechanical solution for composite vessels and the satisfaction of the main failure criteria. An innovative approach lies in the possibility of using the developed optimization methodology for designing vessels with non-symmetrical filament winding, which have unequal polar openings on the domes. This became possible due to the development of a special numerical mechanical finite element model of a composite vessel. A specific Python program provides the creation of a model and controls the exchange of data between the modules of the iterative optimization process. The numerical model includes the determination of the distribution of fiber angles on the domes and cylindrical part of the vessel as well as changes in layer thicknesses. The optimization problem solution is provided using a Multi-Island Genetic Algorithm, this type of method showed its efficiency for such applications, by allowing to avoid local solutions. Thus, optimal parameters of a composite vessel were found by minimizing composite mass and thickness and maximizing the strain energy. Test solutions using the developed methodology are presented for three types of composite materials to evaluate their possibility for integration into the vessel design model. [ABSTRACT FROM AUTHOR]

Filament-wound Composite Pressure Vessels (CPVs) are employed largely for gas or fluid storage under pressure in aerospace, automotive and naval industries. Composite vessels are subjected to harsh conditions such as critical loadings, extreme temperatures, and bursting; therefore, a permanent in-situ and online monitoring approach for the structural integrity of the vessels is essential. Hence, this review paper focuses on the description of the most trending used sensors such as piezoelectric (PZT and PVDF), piezoresistive (BP and MXene) and fiber optic (SOFO®, OBR and FBG) sensors, for developing a Structural Health Monitoring (SHM) approach to create self-sensing composite pressure vessels. The novelty of this review paper lies in providing an overview of existing works covering the integration of sensors in composite vessels, including sensor types, localization, and their impact on composite integrity. Particularly, an analysis of the literature is provided concerning the sensor's integration and especially their monitored parameters, layout design and arrangement in CPVs. Additionally, the interaction between the host composite material and sensors is analyzed to understand how to integrate sensors with the minimum possible defects that alter the mechanical performance of composite vessels. Lastly, a discussion of a CPV's SHM system is provided to offer researchers a foundation for upcoming experimental work. [ABSTRACT FROM AUTHOR]

Ultrasonic imaging using the Total Focusing Method (TFM) is very useful for locating and sizing defects accurately. However, when imaging clusters of pores, the results may be distorted by multiple scattering phenomena. Several simulations are performed in a 2D context considering different scattering model approaches: single scattering, single scattering including defect shadowing, and multiple scattering. In order to reproduce clusters of pores, we use sets of side-drilled holes to impose well-controlled properties (position and size) for comparison with experimental tests. Comparisons of the simulated TFM images with the experimental ones show qualitative and quantitative improvements when using the multiple scattering model, thanks in particular to a better consideration of shadowing and other interaction effects between defects. • Simulation of the inter-element response matrix (Full Matrix Capture, FMC) using a multiple scattering model (under the hypothesis of far-field scattering coefficients). • Comparison of simulated TFM/FMC reconstructions with experimental measurements for several porosity cluster configurations. • Integration of the computational kernel into the NDT CIVA simulation platform developed by the French Research and Technology Organisation CEA and its partners. [ABSTRACT FROM AUTHOR]

• Fatigue crack propagation from different Through Drilled Holes (TDH) clusters. • Experimental fatigue test and crack propagation modelling. • Mix-mode behaviour using G-Theta method. • Strong dependency on crack paths and defect characteristics. This paper focuses on the fatigue life estimation of metallic components containing a group of porosities as manufacturing defects. In order to represent these defects, six groups of fatigue tests with different Through Drilled Holes (TDH) clusters have been carried out on 7075-T6 aluminium alloy samples. Main characteristics of such defects (of every single hole, spatial density or gradient of elementary sizes) have been studied to determine their influences on the fatigue life. Experimental tensile fatigue tests have been performed on all TDH samples with load ratio R = 0.1. For the finite element simulations of the fatigue crack growth, a semi-elliptical initial crack with size similar to a typical particle of 7075-T6 aluminium alloy has been chosen. Indeed, such a particle is often responsible for crack initiation in this kind of material. For crack growth, the Paris' type propagation law and Forman's law have been used in the modelling. Local stress redistribution due to the presence of the TDH implies mix-mode behavior which has been examined by using the G-Theta method. Simulations results allow realistic lifetime estimations according to the experimental results. Moreover, a strong dependence of the crack paths and fatigue lifetime on the defect characteristics has been proved and quantified. [ABSTRACT FROM AUTHOR]