Data Processing Scheme for Laser Spot Thermography Applied for Nondestructive Testing of Composite Laminates

This paper proposes a data processing scheme for laser spot thermography (LST) applied for nondestructive testing (NDT) of composite laminates. The LST involves recording multiple thermographic sequences, resulting in large amounts of data that have to be processed cumulatively to evaluate the diagnostic information. This paper demonstrates a new data processing scheme based on parameterization and machine learning. The approach allows to overcome some of the major difficulties in LST signal processing and deliver valuable diagnostic information. The effectiveness of the proposed approach is demonstrated on an experimental dataset acquired for a laminated composite sample with multiple simulated delaminations. The paper discusses the theoretical aspects of the proposed signal processing and inference algorithms as well as the experimental arrangements necessary to collect the input data

Damage imaging in composites using nonlinear vibro‐acoustic wave modulations

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VIBROTHERMOGRAPHY FOR IMPACT DAMAGE DETECTION IN COMPOSITES STRUCTURES

The paper investigates modelling aspects related to application of vibrothermography for detection of barely visible impact damage in composite structures. Low-velocity impact tests were performed to introduce multiple delaminations into carbon/epoxy composite plate. Damage severity was revealed using well-established non-destructive evaluation techniques. Vibrothermography was used subsequently to show good agreement with classical damage detection techniques. Following these experimental investigations, numerical simulations were performed to assess feasibility and sensitivity of vibrothermography for impact damage detection. Numerical results were validated using experimental data showing very good qualitative and encouraging quantitative agreement. The study demonstrates that virtual impact damage detection using vibrothermography can be performed as part of structural design to assess sensitivity of the method in real engineering applications. Copyright © 2012 John Wiley & Sons, Ltd

State of art spatial data measurements methods for civil engineering structures

There are many spatial data collection methods, but their characteristics favour ones over another when it comes to engineering structures inspections. Recently, with rapid growth of Unmanned Aerial System technology, their application starts to be appreciated in many scientific fields. In the thesis classical methods of obtaining spatial data: total station positioning and terrestrial laser scanning are presented, and compared with UAS-based photogrammetry. The thesis presents whole process of obtaining data, quality assessment and results comparison. Moreover, Pix4Dmapper Pro, Agisoft Photoscan and Bentley ContextCapture photogrammetry software are tested and analysed with regards of use for spatial engineering structures. For the analysis, Tyholt tower was chosen. It is a concrete cylinder-shaped tower with a number of balconies. It is simple, yet distinct engineering structure, providing good testing field for the study. Obtained results corresponds with initial assumptions when it comes to accuracy, efficiency and workload. The most noticeable contrast while processing was performance of analysed software

The Study of Localized Crack-Induced Effects of Nonlinear Vibro-Acoustic Modulation

The nonlinear interaction of longitudinal vibration and ultrasound in beams with cracks is investigated. The central focus is on the localization effect of this interaction, i.e., the locally enhanced nonlinear vibro-acoustic modulation. Both numerical and experimental investigations are undertaken. The finite element (FE) method is used to investigate different crack models, including the bi-linear crack, open crack, and breathing crack. A parametric study is performed considering different crack depths, locations, and boundary conditions in a two-dimensional beam model. The study shows that observed nonlinearities (i.e., nonlinear crack–wave modulations) are particularly strong in the vicinity of the crack, allowing not only for crack localization but also for the separation of the crack-induced nonlinearity from other sources of nonlinearity

Scaling Subtraction Method for Damage Detection in Composite Beams

Composite materials have been widely used in many advanced engineering structures, because of their high strength and good resistance to fatigue and corrosion. Nevertheless, their susceptibility to impact damage is one of the biggest concerns for use in critical load-bearing structures. Over the last few decades, many non-destructive techniques based on the analysis of nonlinear vibrations and other acoustic phenomena have been developed. Among them, the Scaling Subtraction Method (SSM) is an approach used to extract nonlinear features of an acquired signal generated by the response of a system to an impinging wave, in order to reveal effects that can be associated to internal damage. In this paper, the SSM is applied to examine the response of laminated composite beams to the presence of damage induced by low-velocity impact. The composite beams are tested, both before and after impact, under either impulsive or harmonic excitation of different frequencies, selected among the natural frequencies of the beams. Piezoceramics transducers bonded to the surface of the beam are used for both excitation and sensing. For each harmonic excitation case, the linearly scaled reference signal is compared to the response at large amplitude excitation. An extension of the SSM in the frequency domain is proposed in this paper to detect damage under an impulsive excitation, which typically covers a wide range of frequencies. The results show that this pulse-based extension of the method may be a promising option for detection of nonlinearities associated to damage occurring in composite structures

Force Identification Based on Response Signals Captured with High-Speed Three-Dimensional Digital Image Correlation

Structural Health Monitoring (SHM) systems allow three types of diagnostic tasks to be performed, namely damage identification, loads monitoring, and damage prognosis. Only if all three tasks are correctly fulfilled can the useful remaining life of a structure be estimated credibly. This paper deals with the second task and aimed to extend state-of-the-art in load identification, by demonstrating that it is feasible to achieve it through the analysis of response signals captured with high-speed three-dimensional Digital Image Correlation (HS 3D-DIC). The efficacy of the proposed procedure is demonstrated experimentally on a frame structure under broadband vibration excitation. Full-field vibration displacement signals are captured with the use of two high-speed cameras and processed with 3D-DIC. Loads are identified with two different algorithms based on inverting the Frequency Response Function (FRF) matrix and modal filtration (MF). The paper discusses both methods providing their theoretical background and experimental performance

The study of localized crack-induced effects of nonlinear vibro-acoustic modulation

The nonlinear interaction of longitudinal vibration and ultrasound in beams with cracks is investigated. The central focus is on the localization effect of this interaction, i.e., the locally enhanced nonlinear vibro-acoustic modulation. Both numerical and experimental investigations are undertaken. The finite element (FE) method is used to investigate different crack models, including the bi-linear crack, open crack, and breathing crack. A parametric study is performed considering different crack depths, locations, and boundary conditions in a two-dimensional beam model. The study shows that observed nonlinearities (i.e., nonlinear crack–wave modulations) are particularly strong in the vicinity of the crack, allowing not only for crack localization but also for the separation of the crack-induced nonlinearity from other sources of nonlinearity