Angle Beam Transducers Research Articles

The determination of some sizes and physical characteristics of metals by ultrasound

Recently, ultrasound has found extensive applications in various areas such as industry, medicine, and agriculture. This paper introduces a method of determining the thickness, speed of propagation of ultrasound in metal, and the modulus of elasticity for selected metals by ultrasound. The determination of these properties was done with the NDT USM25 ultrasonic flaw detector by Krautkramer. For this purpose, straight beam contact transducer and angle beam transducers (60o) were used. The presented method offers a practical and reliable way of measuring thickness and other properties of metal and metal alloys.

Debond Identification in GFRP Strengthened RC Beam Using Surface Guided Wave Mode Generated by Angle Beam Transducer

Debond Identification in GFRP Strengthened RC Beam Using Surface Guided Wave Mode Generated by Angle Beam Transducer

Guided waves based debonding classification in lap-joints using modified Fisher discriminant criterion

In this paper, a modified fisher discriminant criterion is used to identify and rank damage sensitive features for debonding classification. For this purpose, the analysis of the correlation between features (ACF) based on Pearson correlation coefficient and the Fisher discriminant ratio (FDR) criterion were combined to select the most relevant features. The debondings classification was evaluated in a multiclass classification by considering three different classes of damage and one class of undamaged. The nondestructive inspection was performed in a composite-adhesive-composite lap-joint using guided Lamb wave testing with angle beam transducers mounted in a pitch-catch configuration. From the collected data, twelve features were extracted by using statistical functions and signal processing techniques. From the extracted features, the most damage sensitive features were selected based on the proposed method (ACF and FDR) and the results were compared using the conventional FDR method. For three different classifiers, the feature selection strategies were tested and their performance evaluated using the metrics: accuracy, precision, recall and F1 score. For the dataset collected in this study, the results support that the proposed method yields an improvement of the performance of the classifiers in comparison with the use of the conventional FDR-based feature selection.

Numerical modelling of ultrasonic guided waves for detection and characterization of debonds in FRP strengthened beams

Debonding failure in fibre reinforced polymer (FRP) strengthened structures is one of the most critical modes of failure. Timely detection of the debonds are vital for the safety of the structure. This study compares the three numerical models of ultrasonic guided wave generation in FRP strengthened concrete beam in an effort to detect and characterize debonds at the concrete-FRP interface. Numerical models of a carbon reinforced polymer (CFRP) strengthened beam with debonds of different sizes are prepared using commercially available finite element (FE) software ABAQUS®. The ultrasonic guided waves are introduced in the beam by the application of narrowband transient vertical and in-plane surface excitations representing contact type and surface bonded piezoelectric (PZT) transducers, respectively. A new model of angle beam transducer is also proposed, aiming to generate a particular guided wave mode in the CFRP strengthened beam. The wedge angle of the transducer is chosen in accordance with Snell’s law so that the desired mode is propagated in the beam. To prevent the reflections within the transducer, infinite elements are used for modelling the transducer boundary. Moreover, to minimise the computational cost, infinite elements are also used in the beam side faces. The models are validated by comparing the group velocity with the velocity obtained by the dispersion curve. Later, extensive parametric studies are conducted with the aim to relate the wave propagation characteristics to the debond sizes. It is found out that the amplitude of hilbert transform of the scattered wave increases with the increase in debond. size.

Investigation of the effect of angle beam transducer parameters on the lamb wave field in the three–layer plate by normal mode expansion method

The effect of angle beam transducer parameters such as wedge angle and width transducer on the Lamb wave field generated in the elastic-viscoelastic three-layer plate has been investigated using normal mode expansion method. At first, the propagation of Lamb wave in the three-layer plate has been investigated using global matrix method, and all the modes that are propagated in the three-layer plate have been specified. Then, the optimum parameters of angle beam transducer have been obtained to generate a mode with minimum attenuation at a specific frequency. In addition to this mode, other modes are also generated in the three-layer plate, but this mode has maximum energy in the three-layer plate. The results indicate that the energy contribution of the mode with minimum attenuation at a specific frequency is 99.9% of the total energy and this mode has the highest energy contribution.

Pure S0 and SH0 detections of various damage types in aerospace composites

This paper proposes a new single-mode guided wave-based method to detect various types of damage in aerospace composites. In this method, single-mode guided wave excitation was achieved using adjustable angle beam transducers (ABT). The ABT tuning angles of various pure-mode guided waves were calculated based on Snell's law applied to the composite dispersion curves. A finite element (FE) simulation of pure S0 mode excitation in a crossply composite plate was conducted and the simulation results were validated by the experiment. For the first time, angle beam transducers were applied to generate pure shear horizontal (SH0) wave in a thick quasi-isotropic composite plate. The pure SH0 wave excitation was successfully verified by a three-dimensional (3D) FE simulation. SH0-mode wave propagation and interaction with delaminations were further conducted and strong trapped waves within the delamination regions were observed. Experiments using S0 or SH0 pure-mode guided waves were conducted to detect various types of composite damage, such as wrinkle damage in the crossply composite plate, multilayer delaminations by Teflon inserts, and actual impact damage in the thick quasi-isotropic composite plate. A significant amplitude drop was observed due to the presence of different composite damage types. In addition, a linear scanning method using pure SH0 wave was also developed to estimate the sizes of delaminations and impact damage. Both numerical and experimental results demonstrated the validity and usefulness of the proposed method for the detection of various damage types in composites.

Multimode Guided Wave Detection for Various Composite Damage Types

This paper presents a new methodology for detecting various types of composite damage, such as delamination and impact damage, through the application of multimode guided waves. The basic idea is that various wave modes have different interactions with various types of composite damage. Using this method, selective excitations of pure-mode guided waves were achieved using adjustable angle beam transducers (ABTs). The tuning angles of various wave modes were calculated using Snell’s law applied to the theoretical dispersion curves of composite plates. Pitch–catch experiments were conducted on a 2-mm quasi-isotropic carbon fiber-reinforced polymer (CFRP) composite plate to validate the excitations of pure fundamental symmetric mode (S0) and shear horizontal mode (SH0). The generated pure S0 mode and SH0 mode were used to detect and separate the simulated delamination and actual impact damage. It was observed that S0 mode was only sensitive to the impact damage, while SH0 mode was sensitive to both simulated delamination and impact damage. The use of pure S0 and SH0 modes allowed for damage separation. In addition, the proposed method was applied to a 3-mm-thick quasi-isotropic CFRP composite plate using multimode guided wave detection to distinguish between delamination and impact damage. The experimental results demonstrated that the proposed method has a good capability to detect and separate various damage types in composite structures.

Comparative Study of Coupling Techniques in Lamb Wave Testing of Metallic and Cementitious Plates.

Lamb waves have emerged as a valuable tool to examine long plate-like structures in a faster way compared to conventional bulk wave techniques, which make them attractive in non-destructive testing. However, they present a multimodal and dispersive nature, which hinders signal identification. Oblique incidence is one of the most known methods to generate and receive Lamb waves and it is applied in different experimental arrangements with different types of sensors. In this work, several setups were conducted and compared to determine the optimal ones to launch and detect ultrasonic Lamb waves, especially in non-homogeneous specimens. The chosen arrangements were contact with angle beam transducers, immersion in a water tank, localised water coupling using conical containers and air coupling. Plates of two different materials were used, stainless steel and Portland cement mortar. Theoretical and experimental dispersion curves were compared to verify the existence of Lamb modes and good correspondence was achieved.

Rayleigh Wave Calibration of Acoustic Emission Sensors and Ultrasonic Transducers.

Acoustic emission (AE) sensors and ultrasonic transducers were characterized for the detection of Rayleigh waves (RW). Small aperture reference sensors were characterized first using the fracture of glass capillary tubes in combination with a theoretical displacement calculation, which utilized finite element method (FEM) and was verified by laser interferometer. For the calibration of 18 commercial sensors and two piezoceramic disks, a 90° angle beam transducer was used to generate RW pulses on an aluminum transfer block. By a substitution method, RW receiving sensitivity of a sensor under test was determined over the range of frequency from 22 kHz to 2 MHz. Results were compared to the sensitivities to normally incident waves (NW) and to other guided waves (GW). It was found that (1) NW sensitivities are always higher than RW sensitivities, (2) differences between NW and RW receiving sensitivities are dependent on frequency and sensor size, (3) most sensors show comparable RW and GW receiving sensitivities, especially those of commonly used AE sensors, and (4) the receiving sensitivities of small aperture (1 mm diameter) sensors behave differently from larger sensors.

Ultrasonic Bulk Waves Measurements for Defect Detection of Composite Materials

The defect detection in composite material is important for its quality control where the hidden defect such as crack, corrosion, notch, holes, void and porosity can develop. In this paper, the ultrasonic bulk wave measurements of longitudinal and shear waves are used to identify defect in the multilayered composite material. This study employs pulse echo technique and utilized angle beam transducer. The composite material model investigated in this contribution are made of 24 mm and 12 mm thick Aluminium plates with a width of 100 mm and a length of 203 mm which are separated with an approximately 1 mm thick oil layer. A simulated defect is created in the composite test material by drilling a hole with 2.5 mm diameter and 3 mm depth on the bottom surface of the third layer material. Finding indicates that the defect is located at 53.39 mm from transducer and the percentage difference of the defect location compared to the calculation method is 7%. It indicates that the proposed method can be use to detect defect in multilayered composite material within 10% accuracy compared to the calculation method.

Method and analysis for determining yielding of titanium alloy with nonlinear Rayleigh surface waves

Methods for determining yielding of titanium (Ti) alloy material with second harmonic Rayleigh ultrasonic wave are investigated. Both piezoelectric angle beam transducers and high frequency laser scanning vibrometer (LSV) are used to detect ultrasonic signals in the Ti alloy specimens with different plastic strain levels. Technical features and outcomes with use of piezoelectric transducers and LSV are compared. The method using piezoelectric transducers, with much higher signal-to-noise ratio than LSV, has been further improved by deploying two transducers with central frequencies corresponding to the fundamental and second order harmonic signals respectively to improve the testing reliability and accuracy. Both the techniques using piezoelectric transducer and LSV demonstrate consistently that the acoustic nonlinearity increases with plastic strain, and the second harmonic Rayleigh ultrasonic wave can be utilized for effective determination of yielding in Ti alloy. Our experiments further show that the acoustic nonlinearity increases gradually with plastic strain at small plastic strain level, and there is a more significant increase of acoustic nonlinearity when the plastic strain reaches a higher level. Microscopic investigations using scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM) are conducted for clarifying the relationship between the observed acoustic nonlinearity and micro-structural changes.

Ultrasonic Beam Models for Angle Beam Surface Wave Transducers

ABSTRACTExplicit three-dimensional (3D) point source and multi-Gaussian beam models are obtained for the Rayleigh waves generated by a surface wave angle beam transducer using an angular plane wave spectrum approach. Simulations show that the multi-Gaussian surface wave beam model agrees well with the point source model while being computationally more efficient. The theoretical predictions obtained with the models are also compared to the experimental measurement results where good agreement with the models is found for both on-axis and off-axis field comparisons.

Theoretical modeling of low-attenuation lamb wave modes generation in three-layer adhesive joints using angle beam transducer

IN THIS PAPER, AT FIRST THE ATTENUATION OF LAMB WAVES IN THREE-LAYER ADHESIVE JOINTS, INCLUDING TWO ELASTIC PLATES BONDED TOGETHER BY A VISCOELASTIC ADHESIVE LAYER, IS INVESTIGATED USING GLOBAL MATRIX METHOD AND THEN SUITABLE INCIDENCE ANGLE IS THEORETICALLY CALCULATED TO GENERATE LOW-ATTENUATION LAMB WAVES USING ANGLE BEAM TRANSDUCER. THEORETICAL BOUNDARY VALUE PROBLEM IN THREE-LAYER ADHESIVE JOINTS WITH PERFECT BOND AND TRACTION-FREE BOUNDARY CONDITIONS ON THEIR OUTER SURFACES IS SOLVED TO FIND A COMBINATION OF FREQUENCIES AND MODES WITH LOWEST ATTENUATION. CHARACTERISTIC EQUATION IS DERIVED BY APPLYING CONTINUITY AND BOUNDARY CONDITIONS IN THREE-LAYER JOINTS USING GLOBAL MATRIX METHOD. PHASE VELOCITY DISPERSION CURVES AND ATTENUATION INTENSITY PLOT IN HIGH AND LOW FREQUENCIES ARE OBTAINED WITH NUMERICAL SOLUTION OF THIS EQUATION BY A COMPUTER CODE FOR A THREE-LAYER JOINT, INCLUDING AN ALUMINUM REPAIR PATCH BONDED TO THE AIRCRAFT ALUMINUM SKIN BY A LAYER OF VISCOELASTIC EPOXY ADHESIVE. TO VALIDATE THE NUMERICAL SOLUTION RESULTS OF CHARACTERISTIC EQUATION, WAVE STRUCTURE CURVES ARE PLOTTED FOR A SPECIAL MODE IN TWO DIFFERENT FREQUENCIES IN THE ADHESIVE JOINT. ALSO, TRANSDUCER INCIDENCE ANGLE IS CALCULATED IN TERMS OF FREQUENCY FOR DIFFERENT MODES USING THEORETICAL METHOD TO GENERATE LAMB WAVE MODES WITH LOW ATTENUATION LEVEL BY ANGLE BEAM TRANSDUCER. THESE MODES ARE RECOGNIZABLE BY TRANSDUCERS IN INSPECTIONS WITH LAMB WAVES BECAUSE OF LOW ATTENUATION LEVEL.

Non-Destructive Testing with Ultrasound in Rails and Ship Plates

This paper deals with finding of defects, such as cracks, breakdowns and inclusions in rails and in ship plates, by ultrasound technique. Pulse echo method and twin beams technique is some of the ultrasonic inspection methods we have used for thickness measurements and for inspection of the welds. Initially, the thickness of rails and ship plates was measured by ultrasound devices using straight beam transducers and then the weldings of these samples were checked by using angle beam transducers.

Acoustic Nonlinearity of Surface Wave in a Fatigued Aluminum Alloy Specimen

This paper reports a case study for the evaluation of surface fatigue damage by using the acoustic nonlinearity of surface waves. A measurement system using contact angle beam transducers was constructed to measure the acoustic nonlinearity of surface waves based on the harmonic measurement. In order to prove the general properties of acoustic nonlinearity, dependencies of the second harmonic amplitude on the fundamental frequency amplitude and the propagation distance were tested first, where the effect of frequency-dependent attenuation was compensated for. The results showed good agreement with the theoretical expectations. Next, an aluminum 6061 T6 specimen, of which the surface was damaged by a three-point bending fatigue test, was experimented on and magnitudes of nonlinear parameter, measured before and after the fatigue test, were compared. We could see a clear increase in the nonlinear parameter after the fatigue test at the central position of the specimen, where the surface fatigue damage was expected to be concentrated. [doi:10.2320/matertrans.I-M2011846]

A knife-edge load traveling on the surface of an elastic halfspace

A load moving on the surface of an elastic halfspace forms a basic problem that is related to different fields of engineering, such as the subsoil response due to vehicle motion or the ultrasound field due to an angle beam transducer. Many numerical techniques have been developed to solve this problem, but these do not provide the fundamental physical insights that are offered by closed form solutions, which are very rare in comparison. This paper describes the development and analysis of the closed form space–time domain solution for a knife-edge load, i.e. a line segment of normal traction, moving at a constant speed on the surface of an elastic halfspace. The various contributions making up the exact solution, obtained with the Cagniard–De Hoop method, produce all the complicated wave patterns from this distributed type of loading. Examples are the transient wave field at the starting position of the load, angled conical and plane waves propagating into the solid, Rayleigh waves propagating along the surface, and head waves spreading and attenuating in specific directions from the loading path. The influence of the load speed on the wave field is investigated by considering the singularities in the relevant complex domains, for each sonic range relative to the bulk wave velocities. The characteristic wave fronts and wave patterns as exhibited by the particle displacements are evaluated for subsonic, transonic and supersonic load speeds.

Rapid thickness measurements using guided waves from a scanning laser source

Guided waves have been effectively used for rapid inspections of plates and pipes. However, the guided-wave technique is not generally used for measuring the remaining thickness in a plate and a pipe due to the difficulties in guided-wave motion. Instead, time-consuming and costly direct contact thickness measurements are still used in practice. This study describes a thickness measurement technique using the A0 mode of a Lamb wave generated by a laser source. A finite element analysis of Lamb wave revealed that this mode propagates with small reflections and mode conversions at a rounded shallow defect and has larger amplitude at thinner regions. Using these characteristics, it is experimentally demonstrated that the distributions of plate thickness were obtained from the amplitude of A0 mode generated by a scanning laser source and received by an angle-beam transducer. The resulting distribution images were obtained at extremely high speed compared to the conventional thickness measurements.

Lamb Wave Interactions with Non‐symmetric Features at Structural Boundaries

AbstractThe paper initially describes on a numerical basis how a Lamb wave would have to perform that has been initiated in a pure mode (either symmetric or anti–symmetric) and what the wave would have to anticipate in terms of mode conversion when being reflected at a surface not perpendicular to its traveling direction. The effects of changing in geometric specifications of non–symmetric artificial features like angle of sloping edge or partially sloping edges are studied. The results obtained from these studies are presented as the reflected and converted parts of the incident wave versus angle of the edge or percentage of the sloped edge. It has been further shown that Lamb waves being generated experimentally by a finite size transducer into a plate like structure thus most likely result in a combination of modes. Reflection of these combined modes at structural boundaries will therefore generate an even more complex coupling of modes. This situation is further aggravated if the structural boundary is not purely perpendicular to the traveling wave but has a slightly varying angle such as it might have to be anticipated at a countersunk rivet, a notch or even more extreme a crack in a metallic component. However from understanding the background of Lamb wave generation, mode separation and superposition, a systematic approach can be established that allows complex Lamb waves, such as they are observed when monitoring true structures, to be interpreted and understood. This approach has been explained on the basis of numerical result obtained from finite element analyses first before proving the findings by some fundamental experiments performed with variable angle beam transducers which demonstrates the difficulties in de–coupling Lamb wave modes and how to handle those coupled modes in terms of structural condition monitoring. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Guided Wave Dispersion Curves Derived with a Semianalytical Finite Element Method and Its Applications to Nondestructive Inspection

In guided wave inspection, dispersion curves and wave structures are indispensable for designing inspection tools and analyzing waveforms. This report describes solutions of the dispersion curves and wave structures with a semi-analytical finite element method and discusses the applications of the dispersion curves and wave structures in guided wave inspection. Formularization of the semi-analytical finite element method revealed that external dynamic loading should be distributed in a shape similar to the wave structure of the desired mode and enabled the analysis of excitation potentials of desired modes with an angle beam transducer. Using a semi-analytical finite element analysis, guided wave tools for inspecting bottom-edges of rails were developed and gave good results for practical use.

Development of New Flaw Depth Sizing Technique in Ultrasonic Testing (3rd Report, Demonstration of Short Path of Diffraction Technique)

This paper deals with a new crack tip diffraction technique named the “short path of diffraction (SPOD)” technique for accurate depth sizing of flaws on the surface opposite to the examination surface in which a pair of an angle beam and a 0-degree transducers is used as a transmitter and a receiver. In SPOD, flaw depth is calculated from a time difference between two echoes of a tip diffracted longitudinal wave, which arises after an incident wave from the angle beam transducer impinges the flaw. One echo is related to a wave traveling directly from the tip to the receiver, and the other is a wave which reflects at the back surface and subsequently travels to the receiver. The two echoes are detected by the 0-degree transducer located right above the flaw. The new technique will be demonstrated by applying to depth sizing of slits and fatigue cracks in austenitic stainless steel blocks, and slits and stress corrosion cracks in welded austenitic stainless steel specimens.