Analysis, realization and experiment of Lamb wave phased arrays for damage detection and imaging in carbon composite structures

Phased array theory is utilized in the unmanned aerial vehicle (UAV) wing box to identify the damage in the structure. The phased array theory has been adapted to Lamb wave propagation to improve the detection ability of local defects in the complex composite structure. The validity of the proposed method is demonstrated by experimental research in which input signals exerted at piezoelectric (PZT) actuators/sensors on the UAV wing box are successfully reconstructed by using the phased array method. The recognition result is shown on a mapped image. The original mapped image uses gray level transformation method to enhance the image identifiable degrees. And the time of arrival of the Lamb wave signal is calculated by Shannon Wavelet. The experiments is done on carbon composite structure using one dimensional PZT linear sensors array exemplifies that phased array theory well utilized in scanning and detecting the damage and the screw loosening in the structure. The original image is processed by the gray level transformation to improve the contrast and the recognition

Novel Approaches for Structural Health Monitoring

The thirty-plus years of progress in the field of structural health monitoring (SHM) have left a paramount impact on our everyday lives. Be it for the monitoring of fixed- and rotary-wing aircrafts, for the preservation of the cultural and architectural heritage, or for the predictive maintenance of long-span bridges or wind farms, SHM has shaped the framework of many engineering fields. Given the current state of quantitative and principled methodologies, it is nowadays possible to rapidly and consistently evaluate the structural safety of industrial machines, modern concrete buildings, historical masonry complexes, etc., to test their capability and to serve their intended purpose. However, old unsolved problematics as well as new challenges exist. Furthermore, unprecedented conditions, such as stricter safety requirements and ageing civil infrastructure, pose new challenges for confrontation. Therefore, this Special Issue gathers the main contributions of academics and practitioners in civil, aerospace, and mechanical engineering to provide a common ground for structural health monitoring in dealing with old and new aspects of this ever-growing research field

Structural Health Monitoring (SHM) systems in aircraft: wing damage detection employing guided waves techniques

The doctoral thesis provides a detailed description of the implementation of methodologies and technologies based on ultrasonic guided waves for Structural Health Monitoring (SHM) on wing structural elements made of composite materials for BVID or hidden flaws detection. The developed methodologies have been first technologically integrated and applied on small scale structural elements, unstiffened and stiffened plates. Subsequently the SHM system was integrated on a full scale wing box demonstrator in order to perform the delamination detection. The implemented SHM system is capable to control a network of surface mounted piezoelectric transducers, to perform Electromechanical Impedance measurement at each transducer, to check the reliability as well as the bonding strength, and to perform an active guided wave screening

Guided wave propagation and scattering in anisotropic composite structures

Carbon fibre reinforced polymer (CFRP) laminates are widely used for aerospace applications as they reduce the weight of structures whilst maintaining mechanical strength. Composites have highly anisotropic material properties and high in-plane strength but poor interlaminar strength, making them vulnerable to barely visible impact damage (BVID) caused by low velocity impacts. Composite damage is multi-modal, consisting of fibre breakage, matrix cracking, and delaminations, with delaminations causing the most significant strength reduction. Guided ultrasonic waves, often generated using a sparse network of sensors bonded to a structure, provide a promising structural health monitoring (SHM) technique for composites. Guided waves propagate along a structure, with energy throughout the entire thickness, making them ideal for rapid, long-range inspection of large areas. In anisotropic materials wave energy is focused along the high stiffness (fibre) directions, resulting in higher amplitude and wave speed in these directions. Waves launched away from the fibre direction are steered towards the fibres. These anisotropic effects could lead to inaccuracies in damage localization if not accounted for. Propagation of the fundamental, flexural (A0) guided wave mode was investigated in an undamaged unidirectional CFRP panel. Anisotropic effects including the directionality of wave velocities, skew angles, and beam spreading were quantified through both finite element simulations and experiments, achieving good agreement with predictions obtained from dispersion curves. Scattering of the A0 mode at an artificial delamination was studied for a quasiisotropic CFRP plate layup. Wave-trapping on top of the delamination, and strong forward scattering at the delamination exit was found. Significantly different scattering behaviour was observed to that of a magnet target, often used to develop SHM systems. Scattering around both damage targets was found to be directionally dependent, with higher amplitudes in the fibre directions of the outermost laminae. Implications for the SHM of composites were discussed