Showing papers on "Ultrasonic testing published in 2014"

Mechanical characterization of CFRP composites by ultrasonic immersion tests: Experimental and numerical approaches

Abstract: We study an innovative experimental approach for the characterization of the elastic response of anisotropic composite materials by ultrasonic immersion tests. In particular, the class of anisotropy and the elastic moduli can be determined starting from measurements of the velocities of ultrasonic waves propagating in suitable directions. To this aim, we have designed and developed a goniometric ultrasonic test bench and a software for the management of the test and the processing of the acquired data. By employing this experimental device, we determine in a non-destructive way the five elastic moduli of a transversely isotropic unidirectional CFRP composite. The experimental analyses are supported by numerical simulations, which are useful for a deeper insight of the propagation phenomena and for enhancing the experimental strategies to be adopted.

Numerical Simulation of Nonlinear Lamb Waves Used in a Thin Plate for Detecting Buried Micro-Cracks

Abstract: Compared with conventional linear ultrasonic inspection methods, which are sensitive only to severe defects, nonlinear ultrasonic inspection methods are better for revealing micro-cracks in thin plates. However, most nonlinear ultrasonic inspection methods have only been experimentally investigated using bulk or Rayleigh waves. Numerical studies, especially numerical simulations of Lamb ultrasonic waves, have seldom been reported. In this paper, the interaction between nonlinear S0 mode Lamb waves and micro-cracks of various lengths and widths buried in a thin metallic plate was simulated using the finite element method (FEM). The numerical results indicate that after interacting with a micro-crack, a new wave-packet was generated in addition to the S0 mode wave-packet. The second harmonics of the S0 mode Lamb waves and the new wave-packet were caused by nonlinear acoustic effects at the micro-crack. An amplitude ratio indicator is thus proposed for the early detection of buried micro-cracks.

Ultrasonic guided wave-based testing technique for inspection of multi-wire rope structures

Abstract: The aim of this paper is to investigate the propagation of ultrasonic guided waves (UGW) along multi-wire ropes with polymer cores and to determine whether it is possible to detect defects and to identify a defective strand inside the internal structure of a multi-wire rope. The modes of UGW that propagate along multi-wire ropes have been identified using modelling wherein dispersion curves are calculated using the semi-analytical finite element (SAFE) technique. The optimal excitation regions were estimated using 3D FE modelling. An ultrasonic testing technique to identify particular defective strands inside the internal structure of a multi-wire rope was developed and verified experimentally.

Numerical simulation and experiment for inspection of corner-shaped components using ultrasonic phased array

Abstract: This paper proposes an effective method for corner-shaped components inspection using ultrasonic phased array. We first improved the finite-difference time domain (FDTD) method by way of averaging properly the different ultrasonic parameters of media on the both sides of interface to simulate ultrasonic wave propagation in dual-layered media. Then, an inspection method for corner-shaped structures using ultrasonic phased array and an iterative calculation approach of delay time based on Snell׳s law for complicated geometries were put forward and described in detail. Experiments on an aluminum alloy 2014 sample were conducted to validate the modeling results and the inspection method. Finally, practical application was carried out to image and size the defect in carbon fiber reinforced plastic (CFRP) corner-shaped specimen, yielding experiment results that are in good quantitative agreement with the true values.

Theoretical investigation of nonlinear ultrasonic wave modulation spectroscopy at crack interface

Abstract: This paper studies theoretical results of a nonlinear ultrasonic method based on interaction of two elastic waves of different frequencies. A virtual Nonlinear Wave Modulation Spectroscopy experiment is performed in the vicinity of a crack described by a model combining classical and hysteretic nonlinearity. Quasistatic response to two frequency excitation was computed and harmonic and intermodulation components were studied. The influence of driving signal parameters and nonlinear parameters on the response is thoroughly discussed. A general way of hysteretic response description based on scaling properties is explained. In case of the combined nonlinear model, an analysis of nonlinear spectral components is performed in complex plane. Based on the complex interaction of classical and hysteretic parts, a method of their separation is proposed.

A support vector machine approach for classification of welding defects from ultrasonic signals

Abstract: Defect classification is an important issue in ultrasonic non-destructive evaluation. A layered multi-class support vector machine (LMSVM) classification system, which combines multiple SVM classifiers through a layered architecture, is proposed in this paper. The proposed LMSVM classification system is applied to the classification of welding defects from ultrasonic test signals. The measured ultrasonic defect echo signals are first decomposed into wavelet coefficients by the wavelet packet transform. The energy of the wavelet coefficients at different frequency channels are used to construct the feature vectors. The bees algorithm (BA) is then used for feature selection and SVM parameter optimisation for the LMSVM classification system. The BA-based feature selection optimises the energy feature vectors. The optimised feature vectors are input to the LMSVM classification system for training and testing. Experimental results of classifying welding defects demonstrate that the proposed technique is highly...

Detection of Delamination in Concrete Bridge Decks by Joint Amplitude and Phase Analysis of Ultrasonic Array Measurements

Abstract: The accuracy and precision of low-frequency (center frequency of approximately 55 kHz) ultrasonic testing for detection and characterization of delamination in concrete bridge decks were evaluated. A multiprobe ultrasonic testing system (with horizontally polarized shear-wave transducers) was used to detect built-in delamination defects of various size, depth, and severity (i.e., thickness) in a test specimen—a 6.1 m×2.4 m×216 mm (20 ft×8 ft×8.5 in.) reinforced concrete slab-built to simulate a concrete bridge deck. The collected data sets were reconstructed applying synthetic aperture focusing technique (SAFT). The reconstructed measurement results were then used to assess the condition of the concrete slab at individual points [point-by-point data collection and two-dimensional (2D) reconstruction] as well as along lines, where data were collected at smaller steps and reconstructed in a three-dimensional (3D) format. The local-phase information was also calculated, superimposed on the reconstruc...

Modeling and characterizing impact damage in carbon fiber composites by thermal/infrared non-destructive testing

Abstract: Thermal/infrared non-destructive testing (T/I NDT) is a particular application of IR thermography. T/I NDT is typically classified for passive and active, as well as for steady-state (stationary) and transient (non-stationary, or dynamic). Active T/I NDT can be classified by: (1) the type of thermal stimulation, (2) the arrangement of a sample and a thermal stimulation source, and (3) the size and shape of stimu l ated area. T/I NDT has proven to be a convenient technique for the detection of impact damage in composite materials due to the following: (1) graphite-based composites are similar to a blackbody by absorption/radiation properties in the infrared (IR) wavelength band, (2) their thermal conductivity is lower than that of metals but higher than of many non-metals thus ensuring reasonable temperature signals at convenient observation times, (3) impact damage leads to thin but laterally-extended air-filled defects which produce considerable thermal resistance to the in-depth heat flux, and (4) T/I NDT is a fast, remote and illustrative technique which, unlike ultrasonic inspection, does not require immersing a sample into water. This paper describes some approaches to thermal detection and characterization of impact damage in carbon fiber reinforced plastic (CFRP) of whose inspection is an important issue in several industrial areas, first of all, in aero space where subsurface defects might lead to catastrophic consequences. Realistic solutions of T/I NDT theoretical problems can be obtained by using 3D numerical models of heat conduction. Direct solutions allow better understanding of heat propagation in defect areas while inverse solutions ensure the evaluation of defect parameters, such as defect depth, size and thickness. Several characterization algorithms are available, with a one-sided T/I NDT procedure being better suited for the characterization of defect depth, while defect thickness is best evaluated in a two-sided procedure. In the case of CFRP composites, the defect characterization approaches are well developed, including the technique of dynamic thermal tomography, which enables a considerable reduction of surface clutter and allows the imaging of separate layers of a composite test sample.

Nondestructive testing of a bottom surface and construction of its profile by ultrasonic tomography

Abstract: A technology for ultrasonic tomography aimed at the detection of flawed zones in unilaterally accessible concrete structures and the determination of their thickness and coordinates was presented. The construction of tomograms was described step by step. The results obtained by the current and previous tomograph variants were given. The tomograms of concrete specimens with specified model flaws and without them were obtained. Results with a lower noise level were obtained using the current tomograph variant. The need for the processing of a set of signals for the diagnostics and monitoring of concrete objects was shown.

Nondestructive Evaluation of Welding Residual Stresses in Austenitic Stainless Steel Plates

Abstract: This article investigates the nondestructive capability of ultrasonic waves in residual stress evaluation of austenitic stainless steel plates (AISI 304L). Longitudinal critically refracted (L CR ) waves are employed to measure the residual stresses. Measuring the acoustoelastic constant through the tensile test is eliminated on the main investigated sample to keep it intact. Another welded plate with the same welding specification, geometry, thickness, and the same material is used to extract tensile test samples. To find the acoustoelastic constant of the heat affected zone (HAZ), a metallographic investigation is done to produce microstructure similar to that of the HAZ in a tensile test sample. A finite element model of welding process, which is validated by hole-drilling method, is used to verify the ultrasonic results. The results show good agreement between finite element and ultrasonic stress measurements which is accomplished nondestructively.

Application of wavelet filtering and Barker-coded pulse compression hybrid method to air-coupled ultrasonic testing

Abstract: Air-coupled ultrasonic testing (ACUT) technique has been viewed as a viable solution in defect detection of advanced composites used in aerospace and aviation industries. However, the giant mismatch of acoustic impedance in air–solid interface makes the transmission efficiency of ultrasound low, and leads to poor signal-to-noise (SNR) ratio of received signal. The utilisation of signal-processing techniques in non-destructive testing is highly appreciated. This paper presents a wavelet filtering and phase-coded pulse compression hybrid method to improve the SNR and output power of received signal. The wavelet transform is utilised to filter insignificant components from noisy ultrasonic signal, and pulse compression process is used to improve the power of correlated signal based on cross-correction algorithm. For the purpose of reasonable parameter selection, different families of wavelets (Daubechies, Symlet and Coiflet) and decomposition level in discrete wavelet transform are analysed, different Barker...

Defect Detection in Thick Weld Structure Using Welding In-Process Laser Ultrasonic Testing System

Abstract: A new approach of non-destructive testing for thick welded structural materials based on laser-ultrasonic technique is investigated. In this study, weld part of structural materials, which should be conventionally inspected after welding, is inspected during welding process in order to save time and cost of manufacturing. The laser-ultrasonic is a method to generate and detect ultrasonic signals by laser beams and has potential to be applied to remote inspection/monitoring of materials under welding at elevated temperature. Bulk longitudinal acoustic wave generated by a Q-switched Nd:YAG laser irradiation and detected as surface vibration by laser interferometer coupled with a long pulse detection laser is used to detect defects around the weld. To overcome the lack of sensitivity of laser-ultrasonic testing on thick welded part having a thickness of more than 100mm at higher temperature, we have originally developed a modified synthesis aperture focus signal processing technique (m-SAFT). The in-process testing with actual piping weld having a thickness of 150mm with high temperature more than 200 degrees C. was demonstrated. By using m-SAFT, an actual weld defect of 1.5mm in diameter at 106mm depth in the specimen was clearly observed. The measurement result well agreed with the result of conventional ultrasonic testing conducted after weld process and also the cross-sectional observation of the specimen. [doi:10.2320/matertrans.I-M2014809]

Thermo-mechanical Analysis of TIG Welding of AISI 316LN Stainless Steel

Abstract: In this research, thermoelastoplastic analysis using finite element modeling was carried out to study the thermomechanical behavior of 316LN stainless steel during autogenous tungsten inert gas welding. The efficiency of nondestructive testing was explored by validating the numerical simulations. Online temperature measurements were performed using infrared thermography. A detailed study of surface and bulk residual stress was performed using numerical modeling, and stress profiles were validated using X-ray diffraction and ultrasonic testing, respectively. Distortion analysis was validated using mechanical measurement. Nondestructive testing was efficiently used to validate the numerically predicted thermo-mechanical behavior of welded components.

Prediction of Building Limestone Physical and Mechanical Properties by Means of Ultrasonic P-Wave Velocity

Abstract: The aim of this study was to evaluate ultrasonic P-wave velocity as a feature for predicting some physical and mechanical properties that describe the behavior of local building limestone. To this end, both ultrasonic testing and compressive tests were carried out on several limestone specimens and statistical correlation between ultrasonic velocity and density, compressive strength, and modulus of elasticity was studied. The effectiveness of ultrasonic velocity was evaluated by regression, with the aim of observing the coefficient of determination between ultrasonic velocity and the aforementioned parameters, and the mathematical expressions of the correlations were found and discussed. The strong relations that were established between ultrasonic velocity and limestone properties indicate that these parameters can be reasonably estimated by means of this nondestructive parameter. This may be of great value in a preliminary phase of the diagnosis and inspection of stone masonry conditions, especially when the possibility of sampling material cores is reduced.

Development of optical equipment for ultrasonic guided wave structural health monitoring

Abstract: This paper presents the development of optical equipment that is suitable for ultrasonic guided wave detection for active SHM in the hundreds of kHz range. In recent years, fiber Bragg grating (FBG) sensors have been investigated by many researchers as an alternative to piezoelectric sensors for the detection of ultrasonic waves. FBG have the advantage of being durable, lightweight, and easily embeddable into composite structures as well as being immune to electromagnetic interference and optically multiplexed. However, there is no commercially available product that uses this promising technology for the detection of ultrasonic guided waves because: (a) the frequency is high (hundreds of kHz); (b) the strains are very small (nano-strain); (c) the operational loads may also induce very large quasi-static strains (the superposition of very small ultrasonic strains and very large quasi-static strain presents a very significant challenge). Although no turn-key optical system exists for ultrasonic guided wave detection, we developed optical ultrasonic guided wave equipment using a tunable laser device. The measurement resolution and sampling speed were considered as the most important criteria in our test. We achieved high sensitive (nano-strain) and high sampling rate. Comparative measurements of low-amplitude ultrasonic waves have been done including FBG, strain gauge, and piezoelectric wafer active sensors (PWAS). Calibration and performance improvements for the optical interrogation system are also developed and discussed. The paper ends with conclusions and suggestions for further work.

Test block for carrying out ultrasonic inspection on residual stress of aluminium alloy pre-stretching board by water immersion

Abstract: The invention provides a test block for carrying out ultrasonic inspection on residual stress of an aluminium alloy pre-stretching board by water immersion, belonging to the field of non-destructive inspection. A method for preparing the test block comprises the following steps of cutting a sample, processing the sample and installing the sample. In the method, the water immersion method is adopted for inspection, and the temperatures in stress calibration and stress measurement processes can be ensured to be consistent by controlling the water temperature not to be changed, thus eliminating the effects of temperature difference on the ultrasonic wave speed and eliminating temperature errors; besides, an automatic scanning frame is adopted instead of manual scanning, so that the distance between a probe and the surface of a material to be measured in the measurement process can be ensured not to be changed, thus eliminating the effects of coupling condition difference on sound propagation time and eliminating the coupling errors. The method is beneficial to non-destructive evaluation of the near surface residual stress of the aluminium alloy pre-stretching board.

Diagnostic ultrasound apparatus and elasticity evaluation method

Abstract: Provided is an ultrasonic diagnostic apparatus provided with an elasticity evaluation technology that an error caused by a tissue structure has been reduced. The ultrasonic diagnostic apparatus that measures a velocity of a shear wave that propagates in a test object by utilizing an ultrasonic wave to evaluate elasticity of the aforementioned test object transmits and receives a first ultrasonic wave to the test object to detect a position and a size of the tissue structure of the test object and to automatically decide a measurement region except the tissue structure, transmits a second ultrasonic wave to the measurement region to make it generate the shear wave, and transmits and receives a third ultrasonic wave to the measurement region to measure an amount of displacement in association with propagation of the shear wave and to calculate the shear wave velocity by utilizing this displacement amount.

Ultrasonic testing and microscopic analysis on concrete under sulfate attack and cyclic environment

Abstract: The damage process of concrete exposed to sodium sulfate attack and drying-wetting cycles was investigated. The water to binder (W/B) ratio and the concentration of sulfate solution were taken as variable parameters. Through the experiment, visual change, relative dynamic modulus of elasticity (RDME) and the surface damage layer thickness of concrete were measured. Furthermore, SEM and thermal analysis were used to investigate the changing of microstructure and corrosion products of concrete. The test results show that the ultrasonic velocity is related to the damage layer of concrete. It approves that an increase in damage layer thickness reduces the compactness and the ultrasonic velocity. The deterioration degree of concrete could be estimated effectively by measuring the surface damage layer and the RDME of concrete. It is also found that the content of gypsum in concrete is less than that of ettringite in test, and some gypsum is checked only after a certain corrosion extent. When the concrete is with high W/B ratio or exposed to high concentration of sulfate solution, the content of ettringite first increases and then decreases with corrosion time. However, the content of gypsum increases at a steady rate. The content of corrosion products does not correspond well with the observations of RDME change, and extensive amount of corrosion products can be formed before obvious damage occurs.

3-D reconstruction of sub-wavelength scatterers from the measurement of scattered fields in elastic waveguides

Abstract: In nondestructive testing, being able to remotely locate and size defects with good accuracy is an important requirement in many industrial sectors, such as the petrochemical, nuclear, and aerospace industries. The potential of ultrasonic guided waves is well known for this type of problem, but interpreting the measured data and extracting useful information about the defects remains challenging. This paper introduces a Bayesian approach to measuring the geometry of a defect while providing at the same time an estimate of the uncertainty in the solution. To this end, a Markov-chain Monte Carlo algorithm is used to fit simulated scattered fields to the measured ones. Simulations are made with efficient models where the geometries of the defects are provided as input parameters, so that statistical information on the defect properties such as depth, shape, and dimensions can be obtained. The method is first investigated on simulations to evaluate its sensitivity to noise and to the amount of measured data, and it is then demonstrated on experimental data. The defect geometries vary from simple elliptical flat-bottomed holes to complex corrosion profiles.