Ultrasonic NDT Research Articles

Determination of a Configuration for Sparse Matrix Phased Array Using Simulated Annealing for Imaging in Ultrasonic NDT

Determination of a Configuration for Sparse Matrix Phased Array Using Simulated Annealing for Imaging in Ultrasonic NDT

Low-velocity impact damage detection in cfrp laminates based on ultrasonic phased-array ndt technique

To investigate the delamination characteristics of CFRP laminates in Barely Visible Impact Damage (BVID) state, Low-Velocity Impact Tests (LVIT) and Non-Destructive Testing (NDT) were employed. The energy thresholds of six diverse ply-stacking sequences of laminates in the BVID state were established utilizing visual inspection and contact measurement methods. Ultrasonic phased-array NDT techniques were employed to evaluate quantitatively the magnitude of delamination damage from different viewpoints, including delamination area, shape, and trend variation. Furthermore, the impact resistance of laminates was qualitatively evaluated by analyzing the distinctive delamination damage forms of various specimens to identify the effects of the ply-stacking sequence. The findings of this study demonstrate that reducing the angle disparity between adjacent plies and minimizing the repetition of identical plies can mitigate delamination damage. Additionally, enhancing the ratio of ±45 and 0° plies can improve the flexural stiffness of the structure. Specifically, the ultrasonic phased-array NDT technique was shown to effectively detect delamination damage within the laminate in the BVID state.

Development of HOIS guidance for ultrasonic NDT for non-intrusive inspection at elevated temperatures

The non-intrusive inspection (NII) of pressure vessels using external in-service ultrasonic NDT has multiple advantages compared to internal visual inspection, including the significant reduction of down-time related costs and safety benefits from avoiding manentry into vessels. The HOIS joint industry project, with support from the Net Zero Technology Centre (NZTC), has recently been focussing on NII of components with operating temperatures of up to 250°C (typical of upstream applications). These inspections are challenging because they require probes to be in contact with the hot surface much longer than for spot thickness measurements. The aim of the work has been to develop recommendations for in-service inspection of components at relatively high operating temperatures, thereby extending the benefits of the NII process, including avoiding or deferring internal visual inspection, to a wider range of vessels. Experimental trials have been performed on test components at up to ~250°C, with an emphasis on scanning ultrasonic systems used for corrosion mapping and weld inspection using TOFD and angled-beam phased-array (PA). The most successful trials gave corrosion mapping and TOFD weld examination results that had similar differences from benchmark values to those achieved in earlier ambient temperature trials. For angled-beam PA, it was found that some trials appeared to have issues with accurate correction of the data for the effects of the elevated component temperature on both the refracted beam angle and signal arrival times. Other trials were more successful in this respect. The lessons learned from trials on both ex-service and manufactured samples are leading to the development of specific guidance for NII at elevated temperatures. The paper highlights the technical challenges associated with ultrasonic scanning systems at elevated temperatures, share the lessons learned from the experimental trials and summarise the guidance developed.

Low-Velocity Impact Damage Detection in CFRP Laminates Based on Ultrasonic Phased-Array NDT Technique

Low-Velocity Impact Damage Detection in CFRP Laminates Based on Ultrasonic Phased-Array NDT Technique

Ultrasonic defect detection in noisy signals by a nonconvex sparse regularization approach

Ultrasonic testing has been an important tool for the detection of hidden defects in materials yet its effectiveness is usually compromised by the noise originated from both the testing system and the material being evaluated. Motivated by the prior knowledge that only a small number of defects or reflectors exist within the tested material thus the measured signal can be viewed as a linear combination of a few echoes, a signal processing method is proposed in this study where a nonconvex sparse regularization method based on lp-norm (0 < p < 1) penalty is employed to suppress noises in ultrasonic NDT signals thus enhancing the effectiveness and accuracy of flaw detection. Based on a specially designed over-complete Gabor dictionary, the nonconvex sparse regularization method is introduced to sparsely represent the noisy signal. After signal representation, noise is suppressed by a pruning operator, facilitating the identification and reconstruction of flaw-reflected echoes. The performance of the proposed method is quantitatively evaluated and compared with competing algorithms using simulated noisy ultrasonic signals in a statistical manner. Experimental results are also presented to demonstrate the effectiveness of our method.

Nonlinear Ultrasonic Detection Enhanced by 3-D Printed Phononic Crystals

Nonlinear ultrasonic methods are a novel non-destructive testing and evaluation technology due to their high sensitivity to micro-defects. However, the inherent nonlinearity of ultrasonic equipment hinders the feature extraction with micro-defects information and limits the full-scale use of nonlinear ultrasonic NDT techniques. In this work, we propose a material-enabled filter using phononic crystals (PCs) as functional units to eliminate the unapplicable inherent nonlinearity component. The PCs composed of mass blocks and connective layers symmetrical about the host plate, are simultaneously processed by melting deposition of PLA. The finite element method with Bloch–Floquet boundary condition is implemented to obtain the bandgap at 100 kHz. Based on the mass-spring model, the mechanism of bandgap formation is proved to be attributed to the negative effective mass density band induced by the local resonance of mass block. The PCs successfully opens a propagation wave transmission gap and eliminates the inherent nonlinearity to improve the nonlinear detection of micro-defects in the aluminum plate. This work provides a useful methodology for the wide application of PC-based nonlinear detection methods in the non-destructive testing field.

Higher Order Mode Cluster ( HOMC) Guided Waves - A novel technique for accurate detection and quantification of hidden corrosion

Corrosion happening at the support regions, under sleeves, in interfaces of the pipes are severe and need reliable assessment. These hidden corrosion vary in nature based on the type of hidden region such as in resting supports, welded sacrificial pads or clamp supports just pipes wrapped in protective wrapping. Ultrasonic NDT plays a major role in the inspection of these supports. Several NDE Techniques exist for such inspection but quantifying the wall loss in an accurate manner depends on the nature and extent of corrosion. A new concept for the improved inspection of corrosion at the support region of pipelines using a short-range ultrasonic guided wave technique that uses a collection of Higher Order Modes Clusters, called here as HOMC* has been developed and verified at several field sites. Ultrasonic guided waves (circumferential or axial modes), once generated will be reflected or transmitted from corrosion and other features on the pipe. Inspection can be carried out from the accessible portion of the pipe . This could be done as an in-service inspection without emptying the pipe. HOMC guided waves are unaffected by the point of incidence of the probe. Accurate Wall loss estimation is possible together with cross sectional profile of maximum thickness loss. Using this information an accurate remaining wall thickness assessment is achieved. The technique has been deployed from pipes 2inches and above and upto 20mm wall thickness.

Ultrasonic imaging of buried defects in rails

The present work addresses the ultrasonic NDT of rails, more precisely of the rail foot. The practical constraint is that transducers must be located on the rail head, whereas the region of interest is the rail foot. Thus, there is no direct acoustic path between the transducers and the region of interest. As classical delay and sum methods cannot be applied to such cases, the goal of the paper is to numerically assess the potentiality of the topological imaging method to investigate the rail foot. Three specific typical rail foot defects are investigated, namely, longitudinal vertical cracks, corrosion pits and rail injuries. Simulating eight transducers with different polarizations, the images obtained show that the detection and approximate location of the various defects are possible.

Comparative Analysis of Ultrasonic NDT Techniques for the Detection and Characterisation of Hydrogen-Induced Cracking.

The article is devoted to the investigation of ultrasonic inspection techniques suitable for detecting hydrogen-induced cracking (HIC) and a high-temperature hydrogen attack (HTHA), which are of great importance in petrochemical and refinery industries. Four techniques were investigated: total focusing method (TFM), advanced velocity ratio (AVR) measurement, advanced ultrasonic backscatter technique (AUBT) and time of flight diffraction method using ultra low angle ultrasonic transducers (TULA). The experimental investigation has been carried out on two carbon steel samples cut off from a heat exchanger of an oil refinery and potentially affected by HIC. It was shown that the AVR technique did not reveal any damage and was not effective in the case of the investigated samples due to a thin damage zone with respect to the total thickness of the samples. The AUBT method enabled us to indicate and classify the presence of the hydrogen-induced damage; however, it is complicated to use in practise due to the need perform measurements exactly at the same position using two transducers of different frequencies. The method is more suitable for the verification of damage at a particular position, rather than for scanning. Both other methods—TFM and TULA—enabled us to identify the presence of HIC in large areas of samples. The obtained results have been verified using a metallographic analysis of the section cut from the side of the sample. The results of metallographic examinations have been compared with indications observed using above mentioned techniques and a good correspondence was obtained. It was demonstrated, that the TFM method can detect cracks with dimensions close to 200 µm, while larger cracks of 2 mm were observed very evidently using a 7.5 MHz phased array. Overall, the results suggested that the TULA method is the most suitable method for the primary detection of hydrogen-induced cracking, while the TFM is recommended for the precise assessment of the extent of the detected cracking.

Simplified Matrix Focusing Imaging Algorithm for Ultrasonic Nondestructive Testing

Full matrix focusing method of ultrasonic phased array has been proved with advantages of good signal-to-noise ratio and imaging resolution in the field of Ultrasonic NDT. However, it is still suffering from the time-consuming data acquisition and processing. In order to solve the problem, two simplified matrix focusing methods are provided in the paper. One provided method is a triangular matrix focusing algorithm based on the principle of reciprocity for the multi-channel ultrasonic system. The other provided method is a trapezoidal matrix focusing algorithm based on the energy weight of the different channel to the focusing area. Time of data acquisition and computational is decreased with the provided simplified matrix focusing methods. In order to prove the validity of two provided algorithms, both side-drilled holes and oblique cracks are used for imaging experiments. The experimental results show that the imaging quality of the triangular matrix focusing algorithm is basically consistent to that of the full matrix focusing method. And imaging quality of the trapezoidal matrix focusing algorithm is slightly reduced with the amount of multi-channel data decreasing. Both data acquisition and computational efficiency using the triangular matrix focusing algorithm and the trapezoidal matrix focusing algorithm have been improved significantly compared with original full matrix focusing method.

High sensitivity ultrasonic NDT technique for detecting creep damage at the early stage in power plant steels

Failures of welded main steam pipes in power station plants are related to cracks forming and propagating in the fine-grained zone, so called heat-affected zone (HAZ). Experience shows that Type IV cracks are indeed some of the most common causes of creep failure for low-alloy ferritic steel pipes and headers in power stations. Typically, crack damage will be characterised by high strain rates in the HAZ and local grain boundary separation, which leads to crack growth. In this paper, the high sensitivity technique for detecting creep damage (Type IV cracking), based on focused ultrasound was implemented. Signal processing algorithms were proposed that enable associating the properties of backscattered signals to the internal characteristics of the metal structure. As the result, the boundaries of the parent metal, HAZ and weld metal in an ultrasonic image can be indicated. The approach was validated on the samples exposed to different levels of creep damage and verified with metallographic analysis. It demonstrated that technique allowed detecting clouds of early stage creep damage.

Features of non-destructive testing of existing masonry structures made of autoclaved aerated concrete units

The article describes the possibilities of non-destructive testing of existing structures, made of autoclaved aerated concrete [AAC] masonry units. Relationships that allow the determination of the normalized compressive strength of autoclaved aerated concrete, were developed with the MDT semi-non-destructive method. The general form of the Neville curve, known from the diagnosis of plain concrete was used, which was calibrated to AAC of nominal density classes 400, 500, 600 and 700. The tests were performed and additional empirical relationships were built, to allow for the influence of density and moisture. Moreover, an ultrasonic non-destructive NDT method calibrated on standard cubic 100 × 100 ×100 mm samples of various densities and moisture, is presented. In addition to the non-destructive ultrasound method, the sclerometric method, calibrated on the entire masonry elements, limited to one nominal density of 600 kg/m3 with varying moisture, was also used. A practical application of AAC strength assessment in the existing masonry structure, has been presented.

Model-assisted reliability assessment for adhesive bonding quality evaluation with ultrasonic NDT

This work proposes a cost-effective technique to evaluate the reliability of adhesive bonding quality assessment with ultrasonic NDT. Detectability of debonding defects and weak bonds in aluminum-epoxy single lap joints was estimated by the model-assisted probability of detection curves. For those adhesive joints containing three different bonding qualities –debonding at the interface, weak bond with release agent contamination, and weak bond due to faulty curing– numerical models were built. Ultrasonic wave propagation was simulated by using the semi-analytical finite element method via CIVA and validated with experimental investigations. In order to create a parametric study, uncertain parameters and their distribution were determined based on experiments and expertise. Ultrasonic signal responses in the time and frequency domain were analyzed as opposed to defect characteristic values. According to reliability analysis, it is shown that the detection probability of debonding is mostly based on the gate selection and ultrasonic echo amplitude, while weak bond detection requires a more delicate assessment. Frequency-based calculations can improve the detection reliability of weak bonds due to release agent contamination. Weak bonds caused by faulty curing can be detected via frequency domain maximum amplitude or the attenuation of the signal response.

Determination of fracture toughness for carbon fiber reinforced plastics free of the crack initiator using the acoustic microscopy

The fracture toughness which reflects change in the elastic deformation energy of the structural element with an increase in the crack area per unit at the onset of straining is one of the crack resistance parameters of carbon fiber plastics (CFRPs). When studying the fracture toughness, the position of the crack front is determined: both the initial one and that obtained as a result of crack growth. Currently existing test standards (STO TsAGI, ASTM D7905) determine the viscosity by the shear mode GIIc using the samples with a crack initiator. However, the method does not reflect the real conditions of crack initiation in CFRPs structures and can lead to a decrease in the accuracy of determining the load of crack initiation. A new technique of the fracture viscosity determination free of the standard delamination initiator has been developed in TsAGI. We present the results of developing the proposed methodology. The GIIc values were determined for a shear crack under three-point bending conditions after wedging. To determine the position and shape of the crack front, as well as to assess the dynamics of its propagation under subsequent loads, we used ultrasonic methods — ultrasonic flaw detection (ultrasonic NDT) and acoustic microscopy instead of the standard visual observation of the crack boundaries from the end surface of the samples. It is shown that acoustic microscopy at a frequency of 50 MHz provides determination of the crack front position in CFRP samples at a depth of 3.0 – 3.5 mm with a high resolution about 100 μm. The features of the crack growth under shear conditions are discussed. The results of the study show that high accuracy of acoustic microscopy in comparison with traditional ultrasonic NDT diagnostics is strongly sought for determining the shape of the cracks, as well as for analyzing the dynamics of crack growth and revealing the mechanisms of interlayer crack propagation in a composite material.

Reconfigurable hardware implementation of coherent averaging technique for ultrasonic NDT instruments

The paper proposed a novel hardware (FPGA) implementation of the coherent averaging architecture for the reconfigurable ultrasonic NDT system. The proposed hardware architecture uses the addressing based shifting technique for the addition operation and Radix-2 non-restoring algorithm for the division operation. Since the amount of hardware required by the proposed averaging scheme is independent of the number of averages, it supports on-the-fly control on the number of averages. Compared to conventional architecture, it provides 96% reduction in memory storage, 98% reduction in the number of adders, and 32% reduction in the processing time for the case of 64 coherent averages. For the experimentation, the ultrasonic imaging system designed and developed by the authors has been utilized. The developed system further supports dynamic on-line reconfiguration of the analog front-end hardware, real-time data acquisition, real-time hardware based data processing, and data transfer operations. The performance of implemented coherent averaging has been presented by various applications such as removal of RF random false-echoes, smoothing of A-scan waveforms and speckle removal of B-scan images.

Ultrasonic NDT determination of initial and final setting time of cement paste

There are several methods for determination of the setting and early hardening in the cementitious composites. The most common method is using the Vicat apparatus. The major disadvantage of this method is that it is invasive and therefore the measurement results exhibit high variability. The paper deals with the continual monitoring of the process of setting and early hardening of a cement paste using the ultrasonic measurement. The innovative method of using the ultrasonic NDT method for determination of the setting times of cement paste is presented in the paper.

A Comparison of Composite Specimens Damage area Measurements Performed using Pulsed Thermography and Ultrasonic NDT Methods

Abstract Carbon fiber reinforced plastics (CFRPs) are widely used in aerospace structures due to their high stiffness, strength and good fatigue properties. They are however vulnerable to loads perpendicular to their plane and, while impacted, can suffer significant internal damage decreasing their overall strength. Detecting and sizing such damage is an important task of the non-destructive inspection (NDI) methods. This study was conducted to detect and quantify damage in a set of six impacted even rectangular CFRP specimens designed from a MiG-29 vertical stabilizer’s skin. The inspection was done using the ultrasonic (UT) method (based on mobile scanner – MAUS V) and the pulsed infrared thermographic (IRT) method. Each specimen’s inside and outside (impacted) surface was inspected separately with IRT, while the outside surface was then inspected with UT. UT provided the most precise measurements of the damage area, while the IRT inspection of the outside surface (which would be accessible on a real aircraft structure) provided underestimated values due to the damage’s depth and geometry.

Dynamic behaviour of composite panels under acoustic loading

PurposeThere are structural elements on the aircraft that may be exposed to high-intensity sound levels. One of them is an air inlet duct of the jet engine. To prepare data for the air duct damage tolerance analysis, flat panels were tested under acoustic loading. The paper aims to discuss this issue.Design/methodology/approachThe acoustic fatigue test equipment for grazing wave’s incidence was designed based on the FE analyses. Flat composite panels were designed and manufactured using the Hexply 8552/AGP193-PW prepreg with the simulation of production imperfections or operational damage. The dynamic behaviour of panels has been tested using three regimes of acoustic loading: white noise spectrum, engine noise spectrum and discrete harmonic frequencies. The panel deflection was monitored along its longitudinal axis, and the ultrasonic NDT instruments were used for the monitoring of relevant delamination increments. The FE model of the panel was created in Abaqus to study panel dynamic characteristics.FindingsNo delamination progress was observed by NDT testing even if dynamic characteristics, especially modal frequency, of the panel changed during the fatigue test. Rayleigh damping coefficients were evaluated for their use in FE models. Significant differences were found between the measured and computed panel deflection curves near the edge of the panel.Originality/valueThe research results underscored the signification of the FE model boundary conditions and the element type selections when the panel works like a membrane rather than a plate because of their low bending stiffness.

Investigating vibration characteristics of magnetostrictive transducers for air-coupled ultrasonic NDT of composites

In this study, high-power ultrasonics has been used for non-contact nondestructive testing of composites. Air-coupled magnetostrictive ultrasonic transducers provide reasonable amplitudes of horn oscillations even if this type of ultrasonic stimulation is close to the idle mode. Four types of ultrasonic horns have been designed and manufactured in order to choose an optimal horn configuration. For each horn, the dependence of vibration amplitude on ultrasonic unit power has been found to exhibit a good match between the theoretical and experimental results. The resonance frequencies and amplitudes of oscillatory velocity were experimentally evaluated by using the technique of scanning laser vibrometry and modeled by means of the Autodesk Inventor software. An air-coupled magnetostrictive transducer, in conjunction with an optimized horn, has been used in the evaluation of impact damage in a graphite epoxy composite and detection of water and excessive epoxy adhesive in an aviation honeycomb panel. It is expected that the technique of air-coupled ultrasonics may be useful for inspecting thin, fragile and hydrophilic materials.

Effect of processing parameters and void content on mechanical properties and NDI of thermoplastic composites

Several consolidation cycles were performed to study the impact of processing parameters on void content, ultrasonic NDT and mechanical performance of CF/PEEK composites. A series of [+45/−45]4S laminates were manufactured by out-of-autoclave technologies including vacuum bag only, hot-press, and automatic lay-up with in-situ consolidation. A range of porosity between 0 and 19% of void content was assessed by varying the processing temperature from 340 to 500 °C and pressure from 0.25 to 1.5 MPa. Void content, shape and location were characterized by using C-scan, matrix digestion and 2D microscopy. Mechanical characterization including in-plane shear and interlaminar shear testing was performed. The results show a critical void content where properties start to decrease at a given drop-off rate. The results suggest that each processing technology should have its own quality control criteria. The proposed methodology is useful for engineering applications of thermoplastic composites and the creation of NDT acceptance criteria.