Application of signal processing techniques to ultrasonic ToFD testing of austenitic welds

The desired properties of austenitic steels lead to their numerous applications in many industries. Welded austenitic materials have columnar grains, anisotropic elastic properties, and a heterogeneous structure. These properties are controlled by both the procedure and parameters of welding. The complex structure of austenitic welds can distort and scatter the ultrasonic beams. In ultrasonic testing of austenitic welds, this situation can lead to low signal-to-noise ratio and make the interpretation of results quite difficult. In this paper, the relatively new ultrasonic technique of time-of-flight diffraction (ToFD) is used for inspection of austenitic welds. Special signal processing techniques are implemented in order to improve the low signal-to-noise ratio of ultrasonic signals and make the interpretation of results easier

بررسی اثر درز جوش طولی لوله در هنگام بازرسی فراصوتی لوله با امواج هدایت شده متقارن

Low-pressure fluid transmission lines are largely manufactured by cold rolling of a plate followed by resistance welding of the two edges of the plate. Consequently, these pipes have a straight weld seam along their length. In this paper, a finite element method is used for simulating the propagation of symmetric guided wave modes L(0,2), L(0,1) and T(0,1) in straight seam welded pipes. A comparison is made between the propagation of these wave modes in seamless and seam welded pipes. Results indicate that the angular amplitude profiles of the L(0,2) and T(0,1) modes do not change much in the presence of the seam weld. However, the presence of the straight seam weld significantly affects the propagation of the L(0,1) mode along the pipe. While the angular displacement profile for the L(0,2) and T(0,1) modes are almost symmetric, for the L(0,1) mode, the angular displacement profile shows high asymmetry. This asymmetric behavior impairs the sensitivity of this mode to the detection of defects in the proximity of the weld line. As a result, the guided wave modes L(0,2) and T(0,1) are considered to be suitable for inspection of straight seam welded pipes but L(0,1) is not recommended for this purpose

تحلیل اجزای محدود آزمون غیرمخرب دمانگاری ارتعاشی به کمک فرکانس تشدید عیب

Vibro-thermography is an emerging and promising technique that uses ultrasonic elastic waves as an excitation source to detect and evaluate surface and subsurface defects. Friction of the edges of defects, viscoelastic behavior and non-linear vibrations of the defect region are the main sources of heating and the temperature gradient that shows up synchronously with variations of non-linear elastic energy. The temperature gradient in the defect region can be imaged by an infrared camera in order to estimate the location and size of the defects. In this paper, the vibro-thermography is simulated in COMSOL Multiphysics software. Lamb waves are used to excite an aluminum plate containing a flat-bottomed hole. First, the resonance frequency of the defect is found by means of the theory of vibrations and also by finite element method (FEM). An algorithm that incorporates frequency analysis as a function of out-of-plane displacements is used to verify this frequency and the results are compared with the eigenfrequency analysis results. The agreement observed between the theoretical and numerical models is found to be very good. The plate is then excited by an amplitude modulated sine-burst at the local defect resonance (LDR) frequency and a frequency related to the thermal penetration depth. Thermal image processing is carried out on the thermal waves to obtain their amplitude and phase images. By considering a four-point algorithm, the location, size and geometry of the defect is estimated with good accuracy

Linear and nonlinear guided wave imaging of impact damage in CFRP using a probabilistic approach

The amount and variety of composite structures that need to be inspected for the presence of impact damage has grown significantly in the last few decades. In this paper, an application of a probabilistic ultrasonic guided wave imaging technique for impact damage detection in carbon fiber-reinforced polymers (CFRP) is presented. On the one hand, a linear, baseline-dependent, technique utilizing the well-known correlation-based RAPID method and an array of piezoelectric transducers is applied to detect impact-induced damage in plate-like composite structures. Furthermore, a baseline-independent nonlinear extension of the standard RAPID method is proposed, and its performance is demonstrated both numerically and experimentally. Compared to the conventional RAPID, the baseline-free version suffers from a somewhat lower imaging quality. However, this drawback is compensated by the fact that no damage-free (intact) baseline is necessary for successful imaging of damage

Non-destructive evaluation of kissing bonds using local defect resonance (LDR) spectroscopy : a simulation study

With the growing demand from industry to optimize and further develop existing Non-Destructive Testing & Evaluation (NDT&E) techniques or new methods to detect and characterize incipient damage with high sensitivity and increased quality, ample efforts have been devoted to better understand the typical behavior of kissing bonds, such as delaminations and cracks. Recently, it has been shown experimentally that the nonlinear ultrasonic response of kissing bonds could be enhanced by using Local Defect Resonance (LDR) spectroscopy. LDR spectroscopy is an efficient NDT technique that takes advantage of the characteristic fre- quencies of the defect (defect resonances) in order to provide maximum acoustic wave-defect interaction. In fact, for nonlinear methodologies, the ultrasonic excitation of the sample should occur at either multiples or integer ratios of the characteristic defect resonance frequencies, in order to obtain the highest signal-to-noise response in the nonlinear LDR spectroscopy. In this paper, the potential of using LDR spectroscopy for the detection, localization and characterization of kissing bonds is illustrated using a 3D simulation code for elastic wave propagation in materials containing closed but dynamically active cracks or delaminations. Using the model, we are able to define an appropriate method, based on the Scaling Subtraction Method (SSM), to determine the local defect resonance frequencies of a delamination in a composite plate and to illustrate an increase in defect nonlinearity due to LDR. The simulation results will help us to obtain a better understanding of the concept of LDR and to assist in the further design and testing of LDR spectroscopy for the detection, localization and characterization of kissing bonds

Visualization of delaminations in composite structures using a baseline-free, sparse array imaging technique based on nonlinear Lamb wave propagation

Environmental factors such as temperature and humidity influence the efficacy of defect imaging procedures based on the identification of changes between an intact state and the current state of a sample/component/structure in the presence of a defect. In this paper, we focus on the Reconstruction Algorithm for Probabilistic Inspection of Damage (RAPID) and propose a nonlinear Lamb wave version of RAPID to visualize a delamination in a composite structure without having to know anything about the intact state, i.e. a baseline free RAPID. Once the optimal frequency selection of Lamb waves in a pitch-catch configuration mode is performed, low and high excitation amplitude signal responses within a sparse array at that frequency are evaluated along each transducer-receiver path by analyzing a set of damage sensitive parameters: the correlation coefficient, the energy of the scaling subtracted signal, and the and the third harmonic ratio. Processing of this information leads to a corresponding probabilistic damage map of the area within the sparse array. The obtained results from a validation experiment demonstrate the capability of this nonlinear variant of RAPID for the identification of a delamination in a composite structur

Non-destructive evaluation of kissing bonds using local defect resonance (LDR) spectroscopy : a simulation study

With the growing demand from industry to optimize and further develop existing Non-Destructive Testing & Evaluation (NDT&E) techniques or new methods to detect and characterize incipient damage with high sensitivity and increased quality, ample efforts have been devoted to better understand the typical behavior of kissing bonds, such as delaminations and cracks. Recently, it has been shown experimentally that the nonlinear ultrasonic response of kissing bonds could be enhanced by using Local Defect Resonance (LDR) spectroscopy. LDR spectroscopy is an efficient NDT technique that takes advantage of the characteristic fre- quencies of the defect (defect resonances) in order to provide maximum acoustic wave-defect interaction. In fact, for nonlinear methodologies, the ultrasonic excitation of the sample should occur at either multiples or integer ratios of the characteristic defect resonance frequencies, in order to obtain the highest signal-to-noise response in the nonlinear LDR spectroscopy. In this paper, the potential of using LDR spectroscopy for the detection, localization and characterization of kissing bonds is illustrated using a 3D simulation code for elastic wave propagation in materials containing closed but dynamically active cracks or delaminations. Using the model, we are able to define an appropriate method, based on the Scaling Subtraction Method (SSM), to determine the local defect resonance frequencies of a delamination in a composite plate and to illustrate an increase in defect nonlinearity due to LDR. The simulation results will help us to obtain a better understanding of the concept of LDR and to assist in the further design and testing of LDR spectroscopy for the detection, localization and characterization of kissing bonds

Nondestructive ultrasonic inspection of friction stir welds

Friction Stir Welding (FSW) is a relatively new solid-state welding procedure developed at The Welding Institute (TWI-UK) and the technique is widely employed for welding aluminum alloys in various applications. In order to examine the quality of the welds and to detect a variety of welding flaws such as wormholes and root-flaws, it is required to develop a methodical inspection technique that can be used for the identification and localization of such defects. The most prevalent and risky defect in this type of welding is the barely visible root flaw with a length varying from 100-700 μm. Due to the extreme characteristics of the flaw, off-the-shelf ultrasonic weld inspection methods are not always able to readily detect this type of minute defect feature. Here, we propose a novel approach to characterize root flaws using an oblique incident ultrasonic C-scan backscattering analysis. The implementation consists of an immersion ultrasonic testing method in pulse echo (i.e. backscatter) mode with a 3.5 MHz transducer, and makes use of an empirical procedure to engender of a shear wave dominated excitation at the root surface, and to properly gate the received signal for root flaw examination. By scanning the surface above the welded component, a C-scan image displaying the backscatter response from the root surface of the nugget zone can be obtained which allows a simple interpretation of the root flaw status of the weld

Nondestructive ultrasonic inspection of friction stir welds

Friction Stir Welding (FSW) is a relatively new solid-state welding procedure developed at The Welding Institute (TWI-UK) and the technique is widely employed for welding aluminum alloys in various applications. In order to examine the quality of the welds and to detect a variety of welding flaws such as wormholes and root-flaws, it is required to develop a methodical inspection technique that can be used for the identification and localization of such defects. The most prevalent and risky defect in this type of welding is the barely visible root flaw with a length varying from 100-700 μm. Due to the extreme characteristics of the flaw, off-the-shelf ultrasonic weld inspection methods are not always able to readily detect this type of minute defect feature. Here, we propose a novel approach to characterize root flaws using an oblique incident ultrasonic C-scan backscattering analysis. The implementation consists of an immersion ultrasonic testing method in pulse echo (i.e. backscatter) mode with a 3.5 MHz transducer, and makes use of an empirical procedure to engender of a shear wave dominated excitation at the root surface, and to properly gate the received signal for root flaw examination. By scanning the surface above the welded component, a C-scan image displaying the backscatter response from the root surface of the nugget zone can be obtained which allows a simple interpretation of the root flaw status of the weld

Improving industrial inspections combining high-frequency flexible ultrasonic arrays and coded excitation

In this study, a commercial 20-MHz 64-element 1 mm-pitch flexible linear array, developed by Novosound Ltd, was evaluated using two different coded excitation techniques to enhance the signal-to-noise ratio and operability on flat and complex-geometry components. Chirp and Golay coded excitation techniques were employed with an arbitrary waveform generation tool to excite the array. A pulse compression technique consisting of a matched filter was implemented, weighted by a Chebyshev window for Chirp excitation