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Early damage in metal materials is primarily characterized by microdefects, such as microcracks and micropores. In this study, we developed a novel approach for quantitatively assessing the microdefect damage degree in dual-phase bainite–ferrite (B + F) X80 pipeline steel using ultrasound nonlinear parameters. A finite element analysis model with micron-scale three-dimensional ellipsoidal defects was established based on the Gurson–Tvergaard–Needleman material damage theory. The propagation process of Lamb waves in the model was simulated to investigate the interaction mechanism between microdefects and Lamb waves and explore the quantitative relationship between ultrasound nonlinearity and microdefect damage degree, which can be characterized by the size and number of microdefects. Furthermore, to validate the simulation findings, an ultrasound testing experiment was designed to evaluate the microdefect damage in (B + F) X80 pipeline steel. The results demonstrate that when Lamb waves propagate through microdefects, their amplitude is attenuated, resulting in changes in ultrasound nonlinear parameters. Within a specific range, the nonlinear coefficient of Lamb waves increases with an increase in microdefect length and number of microdefects but decreases with an increase in microdefect width. This finding holds significant value for evaluating damage degree and predicting the service life of X80 pipeline steel. [ABSTRACT FROM AUTHOR]

Most cracks do not grow straight due to the inhomogeneity of material properties. Furthermore, quantifying structural damage using Lamb waves is difficult due to uncertain crack shape. Here, we present a newly developed finite element model to simulate the propagation of Lamb waves in a cracked plate to quantify the influence of crack size and orientation on the characteristics of Lamb wave propagation. This model includes a piezoelectric actuator and sensor to generate and receive the tone-burst signals of Lamb wave. The damping coefficient of the finite element model was calibrated with the experimental data of plates without a crack. The Lamb wave propagation simulations were performed with various crack sizes, crack orientations, and distances between the actuator and sensor. Our model was utilized to investigate the influence of crack orientation on damage quantification based on the signal phase change and normalized amplitude. We successfully evaluated the effect of the incident angle of the crack, crack size, and distance between the sensors on the change of the plate wave signal characteristics. The signal characteristics obtained from our novel finite element model can be used to develop a quantification model to estimate the crack size, direction, and distance from the sensor. [ABSTRACT FROM AUTHOR]

Purpose: Most Lamb wave-based damage detection techniques use scattering signals obtained from the subtraction of baseline and current signals. This article presents a baseline-free damage detection method based on the signals scattered by the damage in plate-like structures containing a circular hole with edge cracks using guided ultrasonic waves (GUWs) and signal processing. Methods: First, the GUWs were generated by simulating 16 transducers, using finite element analysis and ABAQUS. The location of transducers on the plate were set in a way that similar paths were made for waves traveling from actuators to sensors. Then, the differences between the similar path signals (residual signals) were obtained. The damaged path and arrival time of the scattered wave from the defect to the sensor location were determined using the wavelet coefficients obtained from continuous wavelet transform of the residual signals. Finally, to identify damage locations, arrival time data is applied in a probabilistic approach. Results and Conclusion: The numerical simulation results reveal that the baseline-free approach is able to accurately detect the location of the multiple damages occurred at the hole edge. Further, in order to investigate the effect of the edges of the plate on the results of damage detection, the transducers were considered at different distances from the edge of the hole. By ignoring the damage index values obtained at the edges of the plate, it can be stated that even when the transducers are located near the edges of the plate, the proposed method can detect the crack location at the edge of the hole. [ABSTRACT FROM AUTHOR]

An ultrasonic phased array scanning method was used for lamb wave evaluation of surface and in-depth defects in a steel plate. The ultrasonic guided wave modes resulting from a phased array transducer were modeled using finite element method. The experimental results showed that the high-frequency A0 mode gives acceptable sensitivity and resolution for small diameter through-thickness and surface defects. The sectorial scanning showed better axial resolution rather than spatial resolution. [ABSTRACT FROM AUTHOR]

Analytical expressions are derived for the stresses and electric fields induced in a piezoelectric multilayer deposited on a substrate with lattice misfit and thermal expansion coefficient mismatch. The piezoelectric multilayer can be subjected to an externally applied force, moment and electric potential. The derived formulations can model any number of layers using recursive relations that minimize the computation time. A proper rotation matrix is utilized to generalize the derived expressions to accommodate various orientations allowing each layer to have hexagonal crystal symmetry. The influence of lattice misfit and thermal expansion coefficient mismatch in the presence of externally applied force, moment and electric potential on the state of the electroelastic fields in each layer is evaluated for various applications. Comparison with finite element analysis results shows excellent agreement. The analytical expressions developed here can be useful in designing electromechanical sensors, actuators and optoelectronic devices made from piezoelectric multilayers. [ABSTRACT FROM AUTHOR]

The potentials of high frequency Lamb wave modes are investigated in the inspection of plate-like structures. The wave propagation characteristics of higher order wave modes and the corresponding sensitivity and detectability are studied. Finite element simulations are carried out using infinite elements to model the ultrasonic wedge transducer and the inspection system. Experimental pulse-echo measurements are conducted to verify the influence of different modes characteristics predicted from the finite element simulations. The experimental measurements show a good agreement with the obtained numerical results for the fundamental modes, S and A, and the higher order modes, S and A, at 4 MHz mm of frequency-thickness. [ABSTRACT FROM AUTHOR]

Structural health monitoring (SHM) is becoming very significant for preventing catastrophic failures and uninterrupted operation. Due to continuous developments in SHM Lamb wave technique, finite element simulation is emerging as an initial step to be performed to visualize the potential solution to problem. The present study focus on the simulation of Lamb wave response using finite element method and its application to crack detection and identification in 3D aluminium plates and brass tubes using commercially available finite element package ABAQUS. Phase velocity and group velocity dispersion curve are initially plotted for aluminium and brass material. Subsequently simulation of distinct specimens with and without presence cracks is performed. Simulation results were validated and compared with actual results and were found to be in reasonably good agreement. A damage index parameter i.e. amplitude ratio is defined to notice the effect of crack dimensions variation. Interaction of Lamb waves with rectangular, semi-elliptical and semi-circular cracks (shallow to deep) is studied in detail. Also the application of signal processing techniques such as Spectrogram analysis, Fourier transform and Hilbert transform is also reported in this paper. [ABSTRACT FROM AUTHOR]

Acoustic Emission (AE) method proposed in this paper as a novel approach was used to evaluate residual stress in friction stir welding (FSW) of 5086 aluminum plates. A finite element method was used to evaluate residual stresses in aluminum plates caused by FSW, which was validated by the hole-drilling process. Moreover, fundamental antisymmetric Lamb wave mode ( A ) was implemented to measure the residual stresses produced by FSW process. The novelty of this investigation is the combination of a robust signal-processing analysis and theory of acoustoelastic Lamb wave. In this analysis, an envelope of A mode is used instead of signal time of flight, which obliterates the need to utilize a synchronizing clock of receiving sensors. It was shown that the duration of the signal changes linearly with residual stress variation, and a new equation was then established. Finally, it is confirmed that AE as a nondestructive approach can be an efficient tool for residual stress measurement in welded plate. [ABSTRACT FROM AUTHOR]

The propagation characteristics of laser-generated Lamb waves in multilayered fiber-reinforced composite plates with different fiber orientations and number of layers have been investigated quantitatively. Considering the viscoelasticity of the composite materials, we have set up finite element models for simulating the laser-generated Lamb waves in two types of the multilayered composite plates. In the first type, different fiber orientations are adopted. In the second one, different number of layers are considered. The results illustrate the occurrence of attenuation and dispersion, which is induced by the viscoelasticity and multilayer structure, respectively. [ABSTRACT FROM AUTHOR]

This pioneering experimental work is a proof of concept in which ultrasonic flexural waves have been imaged in a spatially and temporally resolved manner. Thin vibrating plates made of mirror glass and carbon/epoxy composite have been used in the experiments. Results obtained via a standard approach (scanning laser Doppler vibrometry) and the novel methodology based on deflectometry have been compared with a multi-physics finite element simulation. There is a very good correlation between the two experimental techniques. The numerical model provides insight into the experiments, but differs in its detailed structure due to uncertainties over material properties. The extreme slope resolution of deflectometry allows the measurement of peak-to-peak deflections of a few tens of nanometres in one shot. The use of an ultra-high speed camera allows for both space and time resolved measurements of Lamb waves which, to the best knowledge of the authors, has never been reported before. The limitations of the technique arise from the need for a flat specularly reflective surface. However, coating is possible for non-reflective materials and extension to moderately curved surfaces is possible in the future. [ABSTRACT FROM AUTHOR]

The numerical simulation of propagation of the S Lamb mode as a pulse through a waveguide with defect is performed with the use of the finite-element method. As a defective waveguide, an isotropic aluminum plate with a groove placed asymmetrically relative to the center is considered. The groove depth is half the plate thickness. It is shown numerically that propagation of the S wave in the groove is ensured owing to conversion of this wave at the groove edges into the lower-order mode and the inverse conversion. [ABSTRACT FROM AUTHOR]