Ultrasonic Nondestructive Testing System Research Articles

Quantitative Measurement and Evaluation of High-Resolution Ultrasonic Sound Fields using a Novel Automated Ultrasonic Immersion Scanner

Ultrasonic probes are an integral part of the automated ultrasonic non-destructive testing and evaluation (NDT&E) systems to detect and size the defects in a wide range of structural materials in production lines. A complete quantitative assessment of the performance characteristics of an application-specific UT probe is needed to be evaluated on the basis of the international standard DIN EN ISO 22232-2. This requirement of full assessment not only improves the quality assurance of the manufactured probes by evaluating the acceptance criteria but also provides the useful technical information to the end-user to optimize the automated ultrasonic testing on-site. In addition, the evaluation of probe characteristics should be carried periodically throughout their service life. In this work, we developed a novel high-precision ultrasonic immersion scanner to evaluate the full ultrasonic probe characteristics which include the squint angle measurement in three different reference planes (XY, XZ, and YZ), RF-signal and its frequency spectrum at water-steel interface, focal distance, focal range, focal width, focal length and also the angle of beam divergence in different planes of the sound field distribution. In the newly developed UT immersion scanner, for the first time, we successfully integrated the high-precision Hexapod with six axes to achieve a few micrometer (~15 µm) spatial-resolution in the measured sound field patterns and a good angular resolution (~0.05°) in the squint angle measurement. In addition, we used a verified UT instrument in accordance with the standard DIN EN ISO 22232-1 to obtain more accurate amplitude values (±0.5 dB) while scanning a test block. The automated scanning, data acquisition, evaluation, visualization and the automated test report generation are carried based on the standard DIN EN ISO 22232-2. The measured sound beam characteristics of both focused and non-focused application-specific ultrasonic probes with center frequencies ranging from 0.2 - 15 MHz using the pulse-echo technique on a 3 mm half-ball steel reflector are presented. In addition, the measured sound beams of an application-specific 5 MHz multi-element transmit-receive (TR) probe using the 3 mm flat-bottomed-hole (FBH) reflector in a steel reference plate are discussed. Finally, the quantitative analysis of the measured sound field results and the acceptance criteria in accordance with DIN EN ISO 22232-2 are discussed.

A new method for motion stability improving of dual-robotic ultrasonic nondestructive testing system

The dual-robotic ultrasonic nondestructive testing (NDT) system equipped with extension arm is an effective means to realize automatic ultrasonic testing of composite semi-enclosed workpieces. However, this cantilever structure amplifies the tiny vibrations of the inspection system, which seriously affects the coupling effect and the resolution of ultrasonic inspection. To solve the problem, this paper proposes a S-shaped acceleration and deceleration feature control algorithm to improve the motion stability and further to improve the inspection resolution of dual-robotic ultrasonic NDT system. Furthermore, the specific steps of S-shaped acceleration and deceleration features control algorithm in trajectory planning of the dual-robotic ultrasonic NDT system are described in detail. Comparative experiments of motion stability show that the acceleration in the x direction at the left and right ends of the detection area decreased significantly, from 0.15 to 0.08 m/s2 and the ultrasonic image of the internal defects have a higher resolution and smoother edges. The improvement plays an important role in promoting the resolution at the left and right ends of the detection area.

Quantitative imaging of printed circuit board (PCB) delamination defects using laser-induced ultrasound scanning imaging

Laser-induced ultrasound scanning imaging is proposed and utilized for the detection of the printed circuit board (PCB) delamination defect in this present study. Initially, based on the principle of laser-induced ultrasound scanning imaging, a three-dimensional mathematical model of the ultrasonic excitation by pulsed laser acting on the surface of PCB is established and analyzed. Furthermore, based on the established laser ultrasonic nondestructive testing system, single-point testing is investigated on the PCB specimen. A-scan experiments were carried out by transmission and reflection approaches, respectively. Moreover, the influence of the signal receiving position on the discrimination of defective signals and the effect of wavelet transform denoising parameters on the signal-to-noise ratio were investigated. Eventually, based on the laser-induced ultrasound scanning imaging inspection system, the defects of simulated debonding flat bottom holes are detected and studied. The different algorithms or parameters (Fast Fourier Transform, variance, extremum, and principal component analysis, etc.) are employed to extract the characteristic information are analyzed. The experimental results are compared with the traditional infrared thermal wave imaging (lock-in thermography). The experimental results indicate that laser-induced ultrasound scanning imaging has the advantages of high-resolution imaging for the defect with a small diameter. Therefore, it is of great significance to study a set of feasible laser-induced ultrasound scanning imaging for PCB delamination defect detection.

Curved path planning based on 3D vision water immersion ultrasonic nondestructive testing

Compared with traditional 2D image processing, 3D point cloud processing has become a hot technology in the industry, but there are few researches applied to nondestructive testing of curved workpieces. This article aims at the non-destructive testing of curved workpieces, using 3D point cloud and robotic arm for water immersion ultrasonic non-destructive testing. Aiming at the 3D point cloud with many outliers, using the commonly used filter in two-dimensional images-the guide filter, the algorithm is improved and used for the filtering and downsampling of the 3D point cloud, and the adjustment of the curved surface workpiece and the robot arm's pose is introduced. Finally, the workpiece was scanned by a robotic arm with a water immersion ultrasonic nondestructive testing system to prove the feasibility of the experiment and improve the detection efficiency of traditional nondestructive testing technology.

Efficient Global Sensitivity Analysis of Model-Based Ultrasonic Nondestructive Testing Systems Using Machine Learning and Sobol’ Indices

Abstract The objective of this work is to reduce the cost of performing model-based sensitivity analysis for ultrasonic nondestructive testing systems by replacing the accurate physics-based model with machine learning (ML) algorithms and quickly compute Sobol’ indices. The ML algorithms considered in this work are neural networks (NNs), convolutional NN (CNNs), and deep Gaussian processes (DGPs). The performance of these algorithms is measured by the root mean-squared error on a fixed number of testing points and by the number of high-fidelity samples required to reach a target accuracy. The algorithms are compared on three ultrasonic testing benchmark cases with three uncertainty parameters, namely, spherically void defect under a focused and a planar transducer and spherical-inclusion defect under a focused transducer. The results show that NNs required 35, 100, and 35 samples for the three cases, respectively. CNNs required 35, 100, and 56, respectively, while DGPs required 84, 84, and 56, respectively.

Meso-Simulation and Experimental Research on the Mechanical Behavior of an Energetic Explosive

This study establishes a model for polymer-bonded explosives (PBX) using Digimat-FE. The model identifies the relationship between the material’s effective elastic modulus and the explosive particle volume fraction, shape and gradation, and porosity, as well as other factors. Further, finite element analysis of the stress distribution of the PBX composite material is performed, and the mathematical models between the ultrasonic attenuation coefficient, particle volume fraction, and ultrasonic frequency are established. Finally, an efficient ultrasonic nondestructive testing system is designed to determine the stress distribution and fine crack groups in the material. Experimental results indicate that the relative error of stress detection is within 15%, which meets the requirements of engineering applications.

Ultrasonic Non-Destructive Testing System of Semi-Enclosed Workpiece with Dual-Robot Testing System.

With the rapid development of material science, more and more workpieces, especially workpieces with complex curved surfaces, are being made of composite materials. Robotic non-destructive testing (NDT) systems for complex curved surface composite material parts are being used more and more. Despite the emergence of such flexible NDT systems, the detection of semi-enclosed parts is also a challenge for robotic NDT systems. In order to overcome the problem, this paper establishes an NDT solution for semi-enclosed workpieces based on a dual-robot system of synchronous motion, in which an extension arm is installed on one of the robots and presents a trajectory planning method that always ensures the extension arm is parallel to the rotary axis of a semi-enclosed workpiece and that the ultrasonic probes are perpendicular to the workpiece surface. Trajectory analysis experiments and ultrasonic NDT experiments utilizing the optimal water path distance determined by simulation result of multi-Gaussian beam model for two types of semi-enclosed workpieces are performed with the dual-robot NDT system. Experimental results prove that the dual-robot NDT scheme functions well and the planned trajectories are correct. All the hole-shaped artificial defects with diameters ≥3 mm are detected by using 2.25 MHz ultrasonic probes through the transmission testing method. Vivid 3D C-scan image of a small diameter cylindrical workpiece based on the testing result is provided for convenience of observation.

Development of high‐frequency‐type MEMS ultrasonic array sensor using P(VDF/TrFE) thin films

AbstractMEMS (microelectromechanical systems) ultrasonic array sensors were fabricated using the poly (vinylidene fluoride‐trifluoroethylene) [P(VDF/TrFE)] copolymer thin films having multilayer diaphragm structures. For an increased resonant frequency of sensor, we developed a new diaphragm structure. The resonant frequency and sensitivity of new MEMS ultrasonic array sensor was estimated to be on the order of 376 kHz and −75 dBV (1V/Pa = 0 dBV), respectively. This MEMS ultrasonic array sensor can be adapted for ultrasonic 3D imaging and nondestructive ultrasonic testing systems.

Trajectory planning method for improving alignment accuracy of probes for dual-robot air-coupled ultrasonic testing system

Composite workpieces, especially the complex-curved surfaces composite workpieces, have been increasingly used in different industries. Non-destructive testing of these parts has become an urgent problem to be addressed. To solve the problem, this article presents a dual-robot air-coupled ultrasonic non-destructive testing scheme and introduces the structure of the system and a general calibration method for the workpiece frame of a dual-robot system in detail. Importantly, this article proposes a tangential constraint method, which makes the probes completely aligned during the inspection process. Verification experiments and ultrasonic testing experiments for a glued multilayered composite workpiece were performed using the dual-robot air-coupled ultrasonic non-destructive testing system. A comparative experiment was also performed using a dual-robot water jet-coupling ultrasonic testing system. Experimental results show that the dual-robot non-destructive testing scheme and the tangential constraint method function well, and all the artificial defects on the sample can be detected by both kinds of testing methods. Vivid 3-D C-scan image based on the test result is provided for convenience of observation. In other words, a kind of flexible versatile testing platform with multiple degrees of freedom is established.

Crack detection in monocrystalline silicon solar cells using air-coupled ultrasonic lamb waves

In recent years, solar energy becomes one of the most popular renewable energy resources. Among the solar energy systems, solar cells are considered to be one of the most critical components, which are naturally fragile during either fabrication or service. Thus, nondestructive examination of solar cells is required practically. In this research, solar cells made from monocrystalline silicon are selected as the typical samples. The air-coupled ultrasonic nondestructive testing system, based on the generation and reception of the A0 mode Lamb waves, will be adopted for defects detection. Firstly, the dispersion curves of Lamb waves in anisotropic monocrystalline silicon are calculated theoretically, which provides a theoretical foundation for analyzing the behavior of Lamb waves propagating in silicon solar cells. Then, experiments on monocrystalline silicon solar cells are carried out by introducing the air-coupled ultrasonic Lamb waves. The amplitude distributions of Lamb waves propagating along various rotation angles in silicon solar cells are obtained. It shows a strong anisotropic properties of the tested samples. Finally, artificial cracks in solar cells are scanned circularly and laterally. The results of amplitude distributions give the scattering pattern of cracks, which can be used to determine whether the crack breaks through or not. And the extracted amplitude cross-correlation coefficients can help to estimate the length of them.

Offline correction of tool path deviations for robot-assisted ultrasonic nondestructive testing

Introducing industrial robots into ultrasonic nondestructive testing systems makes it possible to test more complex structures. However, the tool path planned in offline programming software may not fit with the actual path in practice, reducing the detection resolution of the system. This paper describes a robot-assisted ultrasonic nondestructive testing system and presents an approach to correct tool path deviations. A feature contained in normal vector angles is used to describe three-dimensional point clouds, in which a matching algorithm is used to calculate the deviations between two point clouds. In this system, the point cloud is measured by an ultrasonic probe, based on the time-of-flight principle. A metal part is used in experiment to demonstrate the effectiveness of the approach. Distance deviations of 0.3–3.0 mm can be corrected. With a detection resolution of approximately 0.3 mm, artificial defects 1.0 mm in diameter and 15.0 mm in depth can be seen more clearly in C-scan images after correction.

Analysis of the continuous mode conversion of Lamb waves in fiber composites by a stochastic material model and laser vibrometer experiments

The complex internal structure of modern laminate composite materials, for example, carbon fiber reinforced plastics (CFRP), has a pronounced influence on the propagation of elastic guided waves (GWs). Along with the well‐known anisotropy‐conditioned amplitude and dispersion directivity of source‐induced wavefields and their remarkable attenuation due to the polymer matrix viscosity, continuous mode conversion (CMC) of GWs in multilayered composites fabricated from unidirectional prepregs has been recently observed experimentally. The latter means that the symmetric fundamental mode continuously converts into the antisymmetric one without passing a damage, that is, even in an intact structure. Being strongly related to the inhomogeneous CFRP microstructure and possessing remarkable intensity for specific propagation directions, this phenomenon should be accounted for in ultrasonic nondestructive testing and structural health monitoring systems. In this work, we investigate the CMC phenomenon in an important class of laminates, namely cross‐ply ones, experimentally as well as numerically. In the computational model it is addressed through the concept of spatially varying material properties, and the finite element method (FEM) is employed for the GW propagation simulation. Experimental measurements are performed for piezoelectrically excited GWs with scanning laser Doppler vibrometry technique, allowing clear visualization of the CMC phenomenon and confirming theoretically predicted dependence of its intensity from propagation direction.

Ultrasonic Adaptive Detection for Aerospace Components with Varying Thickness

Automatic inspection of microdefects located in the aerospace components is difficult due to the imprecise scanning trajectory, especially for those specimens with varying thickness. In this paper, a new ultrasonic nondestructive testing (NDT) system using the robotic scanning trajectory is constructed for inspecting turbine blades. Additionally, an approach based on the analysis of ultrasonic signals is proposed to calibrate the trajectory; the ultrasonic image based on the threshold function represents the distribution of inner defects when the following gate is used to track the flaw echo. Therefore, the characteristic parameters of the flaw echo signals are easy to be discriminated if the reflection waves are stable in the time domain. Experimental result verified the effective and feasibility of the proposed approach; the distribution of inner defects can be shown with a higher resolution than other NDT methods when robotic orientation is correct at each point of scanning trajectory. Furthermore, the feature signals can be tracked more accurately during the ultrasonic signal processing if the ultrasonic distance was considered as a calibration coefficient of positional matrix. The proposed ultrasonic adaptive detection is adapted to complex geometric structure with a minimum resolution of equivalent diameter of the inner flaw being 0.15 millimeters.

The Development of an Automatic Ultrasonic Non-Destructive Testing System

The testing principle of metal ultrasonic is using ultrasonic probe to scan in the work-piece surface, and acquire the probe of reflection signal which is sent to computer to analysis by the ultrasonic data acquisition card so as to detect and locate defects in surface of the parts. This system designed a unique scanning structure using the principle of ultrasonic detection and scans the hardware and software control system to realize internal shape detection for different shape of work-piece.

Extension of the distributed point source method for ultrasonic field modeling

The distributed point source method (DPSM) was recently proposed for ultrasonic field modeling and other applications. This method uses distributed point sources, placed slightly behind transducer surface, to model the ultrasound field. The acoustic strength of each point source is obtained through matrix inversion that requires the number of target points on the transducer surface to be equal to the number of point sources. In this work, DPSM was extended and further developed to overcome the limitations of the original method and provide a solid mathematical explanation of the physical principle behind the method. With the extension, the acoustic strength of the point sources was calculated as the solution to the least squares minimization problem instead of using direct matrix inversion. As numerical examples, the ultrasound fields of circular and rectangular transducers were calculated using the extended and original DPSMs which were then systematically compared with the results calculated using the theoretical solution and the exact spatial impulse response method. The numerical results showed the extended method can model ultrasonic fields accurately without the scaling step required by the original method. The extended method has potential applications in ultrasonic field modeling, tissue characterization, nondestructive testing, and ultrasound system optimization.

Interface wave-modes in comb transducers

An elastic body with periodic teeth of finite height (a comb), insonified by incident ultrasonic wave and applied, with sliding contact, to the surface of another elastic body (a substrate), constitutes a typical arrangement of ultrasonic nondestructive testing system exploiting comb transducers. The arising scattering problem of incident wave on periodic voids between the teeth and the sliding teeth-substrate contact is considered in the full-wave formulation. In physical interpretation, the vibrating teeth generate surface Rayleigh wave in the substrate by the incident wave pressure exerted on the substrate. In fact, the interface waves are generated which differ from the Rayleigh wave in both the propagation velocity and the wave-mode shape. These interface waves, their velocity and modal shape are the main subject of this paper; an approximated formula is presented for the relation between the most important Bloch components of interface modes in the considered periodic system.

3D finite element simulations of an air-coupled ultrasonic NDT system

A single-sided, air-coupled ultrasonic non-destructive testing (NDT) system based on the generation and reception of the A 0 Lamb mode is used for detecting defects in simple or composite structures. Transmitting and receiving transducers, being oriented at the appropriate coincidence angles for the generation and detection of the mode, are fixed and moved together over the sample surface from one end to the other, to scan the area with the defect. This contact-less NDT system is modelled in three dimensions with a finite element-based method. The air-coupled transmitter is modelled by the normal stress that it locally applies on the sample surface, and the air-coupled receiver by integrating normal displacements over corresponding areas selected on the plate surface according to its positions. In this way, beam spreading of both incident and scattered fields is considered. Numerical predictions have successfully been compared with experimental data for various samples: a simple aluminium plate with a through-thickness hole, as a validation case, a glass–polyester composite sample with an impact damage, and then a high-pressure tank made of a titanium liner and a carbon–epoxy winding, with a local disbond hidden in between.

Nondestructive Testing Method in Artificial Intelligence Real Time Systems

Modern sonar and radar measurement systems are widely used in the field of nondestructive testing for a long time. Usually reference signal is emitted towards the object to be investigated and we get a signal, which is the sum of reference signal reflected from different plies. The task of signal processing is to determine time instances corresponding positions of certain ply, which allow analyzing structure of object. Usually the cross correlation function (CCF) of transmitted sequence and received sequence is calculated. If peaks were clearly identified in the cross correlation function (CCF), it would be easy to determine time instances. Due to the noise some coherent peaks, additive to the expected peaks, appear on the CCF, which are confusing in regard to the clear distinction of target. In order to cancel effects of noise as much as possible some measures have to be taken for data manipulation noise cancellation, such as averaging, inverse filtering and so on. These signal-processing methods need a lot of floating point floating point operations and are time consuming. That is why the usage of such ultrasonic systems is limited in real time systems, which are the base for self-organizing systems. Amount of calculations depends on the length of reference signal, the length of reflected signal to be processed and the noise reduction method used in such system. A new system with reduced amount of calculations is considered in this article. In this system only parts of reflected signal corresponding peaks of CCF are processed. These parts are defined in acquisition mode and afterwards system enters measurement mode. New noise reduction method based on wavelet transforms coefficients thresholding is applied in this system. The length of reference signal impacts system noise immunity and amount of calculations. The main problem in ultrasonic non-destructive testing systems is to cancel out effects of the noise. The optimal length of reference signal for wavelet based signalprocessing method is defined. All these measures allowed significantly reduce amount of calculations in the self-organizing systems.

Noncontact ultrasonic diagnostics in concrete: A preliminary investigation

The use of ultrasonics is well-established in concrete diagnostics. Most current systems use narrow-bandwidth piezoelectric transducers, which must be in contact with the concrete surface. New ultrasonic nondestructive testing (NDT) systems combine electrostatic broadband transducers and signal processing techniques such as pulse compression to improve signal-to-noise ratios (SNRs). This permits air-coupled, noncontact (NC) operation which has many advantages. Preliminary experiments with low-power NC equipment, designed for foodstuffs and packaging, indicate that diagnostics can be performed in this manner through at least 75 mm of concrete. The speed-of-sound versus strength relations thus determined differ from those measured previously since the NC system is more sensitive to paste properties than aggregate properties while the converse tends to apply for traditional equipment. There is significant scope for optimising the NC system to achieve greater penetration and diagnostic capability.

Research on an ultrasonic NDT system for complex surface parts

Aimed at internal quality controlling for complex surface parts, an ultrasonic testing system for complex surface parts has been developed using ultrasonic non-destructive testing (NDT) that has the features of strong penetration, good direction, high sensitivity, low cost, and being harmless to people and materials. The technologies of the computer, numerical control (NC), precision mechanisms, signal analysis and processing were integrated in the testing system. The system includes a PC, a system software, an ultrasonic data acquisition card, a stepper motor drive card and a five-axis precision mechanical device, etc. The software was developed using Windows 98-based VC++. According to CAD data of the parts and interpolation methods, the scanning programs can be programmed. The five-axis scanning system is driven by the CNC (computer numerical control) system to control the attitude of ultrasonic probes. The system’s automatic scanning for complex surface parts, the real-time acquisition of ultrasonic data, and automatic identification of flaw signal have been realized. This system can be used not only for testing complex surface parts, but also, for the random testing of curved parts. With a fast testing speed, high sensitivity, high testing precision and high reliability, the system has wide adaptability.