Nonlinear Ultrasonic Method Research Articles

Influence of thermal damage on linear and nonlinear acoustic properties of granite

Thermally induced damage in Westerly granite subjected to heating/cooling cycle at different temperatures was characterized using linear and nonlinear ultrasonic methods. With the increase of material damage, pulse experiments revealed that linear wave velocity decreased down to nearly 50% of its initial value. The method of inverting wave velocities, according to a non-interactive crack effective medium theory, allowed the quantitative evaluation of the crack density, compared to the one obtained with optical observations of the microstructure of the samples. Nonlinear ultrasonic measurements were performed by emitting 1MHz tonebursts at increasing excitation amplitude. With increasing damage, the obtained waveform appeared to transform into the second time derivative of the envelope of the emitted toneburst, revealing a self-demodulation effect. To characterize the changes with increasing damage quantitatively, a self-demodulation index is introduced. This parameter reflects the change in linear attenuation and the nonlinearity of the material in a combined manner and decreases down to 10% of its initial value, showing the high sensitivity of nonlinear ultrasonic methods compared to linear ones. A simple theoretical model, taking into account a nonlinear stress/strain relationship of the medium, provides analytical solutions of the transmitted waveforms and reproduces well the experimental results.

Pitting damage imaging by non-linear ultrasonic technique: comparison between resonance and non-resonance modes

A non-linear ultrasonic method was applied for evaluating the cavitation damage, so-called pitting damage, in the mercury target of the Japan Spallation Neutron Source (JSNS). First, pitting damage was imposed on disk specimens in mercury using the magnetic impact testing machine (MIMTM) with various numbers of impacts (0, 104, 105, 106, 107 and 108). The pitting damage was imaged with resonance and non-resonance modes, respectively, by employing a non-linear acoustic imaging system. Waveform attenuation and generation of higher harmonics, which have high relevance to the degree of pitting damage, were useful for the imaging. Combined with the attenuation phenomenon, the resonance mode imaged the micropits with higher harmonics more effectively with higher harmonics, compared with the non-resonance mode.

Damage Detection of Closed Crack in a Metallic Plate Using Nonlinear Ultrasonic Time Reversal Method

Initial cracks in metallic structures incline to be closed at rest. Such incipient damage generally fails to be detected and located with traditional linear ultrasonic techniques because ultrasonic waves penetrate the contact area of the closed crack. In this paper, an imaging algorithm based on nonlinear ultrasonic time reversal method is proposed to detect closed cracks in aluminum plates. Two surface-bonded piezoelectric transducer arrays are used to generate, receive, and reemit ultrasonic wave signals. The closed crack is simulated by tightening a bolt on the aluminum plate. By applying large amplitude excitation voltage on the PZT transducers, the closed crack could be opened and closed. The transmitted waves recorded by PZT array contain nonlinear components, the signals are time reversed and emitted back, and the tone burst reconstructions are achieved. The linear reciprocity and the time reversibility break down due to the presence of the nonlinear components. The correlation coefficient between the original excitation signal and the reconstructed signal is calculated to define the damage index for individual sensing path and is used to develop an imaging algorithm to locate the closed crack on the plate. The experimental results demonstrate that incident wave signals and their reconstructed signals can be used to accurately detect and locate closed cracks.

Application of ultrasonic methods for early detection of thermal damage in 2205 duplex stainless steel

Early thermal damage in 2205 duplex stainless steel which is caused by the precipitation of second phases during a short term exposure to high temperature (700°C) is investigated. Nonlinear ultrasonic measurements are performed and their results are compared with those from ultrasonic velocity and attenuation measurements. Experimental results show that the measured acoustic nonlinearity parameter is more sensitive than the ultrasonic longitudinal velocity and attenuation to the precipitation of chi and sigma phases early in the aging treatments. The results from the nonlinear ultrasonic measurements are also supported with those from the scanning electron microscopy (SEM), Rockwell C hardness and Charpy impact test. Especially notable is the close correlation between the hardness and the nonlinearity parameter. This research therefore proposes the nonlinear ultrasonic method as a nondestructive assessment means for early detection of thermal degradation of mechanical properties in 2205 duplex stainless steel.

Monitoring of the Damage Evolution in Reinforced Concrete Girder by Means of Nonlinear Elastic Wave Spectroscopy

Nonlinear elastic wave spectroscopy (NEWS) is a package of advanced methods of ultrasonic spectroscopy which make it possible to capture with a high level of sensitivity the formation and development of structure damage even in materially, as well as geometrically, highly complicated specimens. Concrete and reinforced concrete are classical examples of materials to which the application of conventional ultrasonic methods is very complicated. This is why they make an ideal medium for the application of non-linear ultrasonic methods. The object of this experimental study consists of the application of nonlinear ultrasonic testing to assess the structural integrity of a reinforced concrete girder which was extracted from a bridge structure during the reconstruction of the bridge. The girder was tested in three stages: prior to loading, in the course of loading, and when the loading had been completed, with the aim of identifying the parameters correlating with the girder structure integrity damage. Two nonlinear ultrasonic spectroscopy methods were applied, namely, employing one and two harmonic signals. Frequency spectra of the transmission responses were analyzed. Defects occurring in the structure under investigation give rise to heavy nonlinear effects accompanying the propagation of elastic waves, which, in the singlesignal excitement case took effect in emphasizing the odd-numbered harmonic components among the newly generated frequencies. Therefore, the amplitudes of the latter were evaluated. In the other case, two ultrasonic signals of close frequencies were applied and their difference components were evaluated. Structure integrity damage was identified in the girder by means of the frequency spectrum analysis.

Characterization of thermally damaged concrete using a nonlinear ultrasonic method

Thermal damage in concrete usually induces contact-type defects, which result in degradation of the concrete's performance. This paper attempts to visualize the thermal damage in a multiscale, and characterizes the thermally damaged concrete using a nonlinear ultrasonic method. An impact-modulation method is used to obtain nonlinearity parameters, as a quantitative measure of contact-type defects, and shows better sensitivity than phase velocity variation as a linear ultrasonic method for thermally damaged concrete. The measured nonlinearity parameter is compared with the permeable pores, which reflect the occurrence of opening and pores in thermally damaged concrete. Degradation of concrete strength due to thermal damage is also assessed via the measurement.

Characteristics of ultrasonic nonlinearity by thermal fatigue

The deterioration conditions of nuclear power plants and chemical plants have raised deep concerns about the safety of high-risk structures. The safety of a structure can be secured by evaluations of breakages and lifespan in the early stage. Therefore, the material condition of a structure needs to be estimated. A nonlinear ultrasonic evaluation method is reportedly more sensitive on microscopic changes of a material than a linear evaluation method. Therefore, the nonlinear ultrasonic technique based on ultrasonic nonlinearity is considered a promising method of evaluation for breakages and lifespan. This study measured the changes in nonlinear parameters by using a nonlinear ultrasonic method, observed the microstructure of a heated material, and analyzed the relation between the size of the microstructure and the changes in the nonlinear parameters.

Nondestructive Evaluation of Early Stage Plasticity and Fatigue Damage of Aluminum Alloy Using Nonlinear Ultrasonic Method

Early stage of plasticity and fatigue damage are difficult to detect by using conventional ultrasonic techniques.Nonlinear ultrasonic technique based on harmonic generation has been shown to have the ability to solve the question.A nonlinear ultrasonic high power transmission testing system is developed to detect early-stage plasticity and fatigue damage of Aluminum 2024-T4 alloy.During the test,the nonlinear parameter of the material based on the amplitude of second harmonic is monotonically correlated with the plasticity and fatigue damage of the samples.The experimental nonlinearities are successfully reduced by using the natural filter effect of piezo-electric discs,which makes the experimental method more robust.The experimental results show that the nonlinear ultrasonic technique based on harmonic generation can be used to detect early-stage plasticity and fatigue damage of aluminum alloy.

Nonlinear Nondestructive Testing and Evaluation: Harmonic Imaging of Kissing Bonds and Micro Damage

Recent advances in harmonic imaging of industrial materials are reviewed. The conventional ultrasonic testing, which is based on acoustic impedance mismatch between contact materials, fails to detect kissing bonds, micro damage and micro defects within a bond layer of dissimilar materials. To the contrary, the nonlinear ultrasonic method, in particular higher harmonic method, makes use of higher harmonics excited at disordered structures mentioned above under incidence of large amplitude of tone-burst waves of a fixed frequency. This review is composed of three parts; key concept of nonlinear ultrasonics, instruments for higher harmonic imaging and harmonic images of kissing bonds, nonmetallic inclusions in metal, creep damage, microcracks in SiC/Ti composite, and weld boundaries. The higher harmonic imaging could be indispensable technique for quality assurance of bonded interfaces of dissimilar materials in near future.

Nonlinear ultrasonic imaging method for closed cracks using subtraction of responses at different external loads

To improve the selectivity of closed cracks for objects other than cracks in ultrasonic imaging, we propose an extension of a novel imaging method, namely, subharmonic phased array for crack evaluation (SPACE) as well as another approach using the subtraction of responses at different external loads. By applying external static or dynamic loads to closed cracks, the contact state in the cracks varies, resulting in an intensity change of responses at cracks. In contrast, objects other than cracks are independent of external load. Therefore, only cracks can be extracted by subtracting responses at different loads. In this study, we performed fundamental experiments on a closed fatigue crack formed in an aluminum alloy compact tension (CT) specimen using the proposed method. We examined the static load dependence of SPACE images and the dynamic load dependence of linear phased array (PA) images by simulating the external loads with a servohydraulic fatigue testing machine. By subtracting the images at different external loads, we show that this method is useful in extracting only the intensity change of responses related to closed cracks, while canceling the responses of objects other than cracks.

Monitoring evolution of compressive damage in concrete with linear and nonlinear ultrasonic methods

An experimental study was conducted on different concrete cylinders damaged in compression. The evolution of damage was followed by means of linear and nonlinear ultrasonic methods, with the purpose to provide a better understanding of mechanical degradation processes in concrete and highlight the potentialities and limitations of the Non-Destructive Techniques used.

Non-linear Ultrasonic Spectroscopy as an Assessment Tool for the Structure Integrity of Concrete Specimens

On the basis of non-linear effect studies, new diagnostic and defectoscopic methods have been designed which are based on the elastic wave non-linear spectroscopy. The non-linear ultrasonic spectroscopy brings new prospects into the acoustic non-destructive testing of material degradation. Poor material homogeneity and, in some cases, the shape complexity of some units used in the building industry, are heavily restricting the applicability of "classical" ultrasonic methods. These linear acoustic methods focus on the energy of waves, which are reflected by structural defects, variations of the wave propagation velocity, or changes in the wave amplitude. However, none of these "linear" wave characteristics is as sensitive to the structure defects as the specimen non-linear response. In this way, non-linear methods thus open new horizons in non-destructive ultrasonic testing, providing undreamed-of sensitivities, application speeds, and easy interpretation. One of the fields in which a wide application range of non-linear acoustic spectroscopy methods can be expected is civil engineering. It is predicted that these advanced techniques can contribute a great deal to the improvement and refinement of the defectoscopic and testing methods in the building industry. The present paper deals with analyzing one of the non-linear ultrasonic defectoscopic methods from the viewpoint of its application to the concrete specimen structural integrity evaluation. Both intact specimens and specimens subject to various kinds of stress have been tested. The effect of structural defects on the elastic wave propagation has been studied.

Impact of Mack Breazeale on the ultrasonic studies of interfaces.

Over the last 50 years, Mack Breazeale made very significant contributions to Physical Acoustics. He was a great influence to his students as well as to researchers all around the world who carried on, continued, and expanded the work which was initiated by him. His work is well known on nonlinear studies of liquids and solids, acousto-optics, ultrasonic interaction at liquid-solid interfaces at the Rayleigh angle generating leaky waves, and many others. Nonlinear acoustic techniques improved material characterization of complex materials and structures significantly. The generation and detection of leaky waves opened up several applications in nondestructive evaluation. In this presentation, several of these techniques which were recently developed will be discussed. One of this is the optical detection of leaky waves at an air-solid interface which can be used to evaluate elastic properties of solids as well as surface imperfections. A nonlinear ultrasonic method to study interfaces between solid layers will be also presented. Mack Breazele leaves a legacy of knowledge, wisdom, and kindness and will always be remembered by us.

초음파의 비선형 특성을 이용한 SUS316L 재료의 피로 열화 평가에 관한 연구

초록:본논문에서는비선형초음파기법을이용하여SUS316L재료시편에서의피로열화를평가한연구의결과를보고한다.초음파의비선형성은입사주파수성분의크기와2차고조파성분의크기비로정의되는상대적비선형파라미터에의해측정된다. 실험을위해접촉식탐촉자를이용한계측시스템을구성하였으며, 안정된비선형파라미터의측정이가능하도록계측시스템자체에서발생되는고조파성분을억제하고계측조건이일관되게유지되도록하였다. 시편으로는SUS316L재료의두가지피로열화시편이사용되었다. 하나는봉형으로회전굽힘피로를가한시편이고, 다른하나는판형으로인장피로를가한시편이다. 피로조건은모두고주기피로에해당한다. 전자는피로가누적되는과정에서비선형파라미터가어떻게변화하는지를관측하는데이용되었고, 후자는피로를가한후피로응력이집중되는위치와그외위치에서의비선형파라미터의차이를관측하는데이용되었다.측정결과비선형파라미터는두가지시편모두에서피로도와강한상관성을갖는것으로나타났다.Abstract: This study evaluated the fatigue degradation in a SUS316L specimen using the nonlinear ultrasonicmethod. Thenonlinearityof theultrasonicwavewasestimatedbyarelativenonlinearparameterdefinedastheratioof theamplitudesforthefundamental wavetothesecondharmonicwave. Intheexperiment, ameasurement systemwith contact transducers was constructed; reliable measurements were assured by keeping measurement conditionsconsistent and reducing extra harmonics generated in the measurement system. Two types of SUS316L specimenwere used in experiments; a rotating bar fatigue specimen and a tensile fatigue specimen. The fatigue conditionused was high cycle fatigue. The former specimen had a cylindrical shape and was used to observe the change inthe nonlinear parameter after fatigue accumulation in a specimen. The latter was a plate-shaped specimen and wasused to confirm the change in the nonlinear parameter at the position where the fatigue stress was concentrated.Themeasurednonlinearparametershowedastrongcorrelationtothedamagelevel inbothfatiguetests.

NDT of Mechanical Damaged Concrete Specimens by Nonlinear Acoustic Spectroscopy Method

Current research and development of non-linear ultrasonic spectroscopy methods shows these methods to be very promising for material testing and defectoscopy in the near future. Our experiments focused on the testing of lightweight concrete specimens using the single-frequency excitation method. We studied the concrete specimens' structure after having been stressed by a mechanical force. Measurements were realized before and after mechanical loading.

Nonlinear Ultrasonic Characterization of Thermally Damaged Westerly Granite

Thermally damaged Westerly granite samples are probed by means of linear and nonlinear ultrasonic methods. With the increase of material damage, linear longitudinal wave velocity decreased down to nearly 50% of its initial value. Nonlinear ultrasonic measurements are performed by emitting 1 MHz tonebursts at increasing excitation amplitude. For increasing damage, the obtained waveform appeared to be the second time derivative of the envelope of the emitted toneburst, revealing a self-demodulation effect. This effect, occuring in a nonlinear manner for increasing excitation amplitude, allows to characterize the material damage with high sensitivity. A simple theoretical model, taking into account a nonlinear stress/strain relationship of the medium, described qualitatively the observed experimental results.

Non-linear ultrasonic evaluation of damaged concrete based on higher order harmonic generation

Non-linear ultrasonic testing, based on higher order harmonic generation, is a true mean for nondestructive evaluation of concrete allowing damage detection at early stages of damage. Using conventional non-destructive testing methods like pulse echo, velocity and impact echo for evaluation of such damages is difficult because poor sensitivity of these methods to early damage occurrence. In this paper an experimental investigation of 18 cubic concrete specimens, caste with three different water–cement ratios, using non-linear ultrasonic technique is presented. The specimens were ultrasonically evaluated both in damaged and undamaged conditions. The specimens were damaged progressively by loading them under compression in several steps up to their ultimate load bearing capacity. At the end of each loading step ultrasonic evaluation was performed and time domain waveforms were recorded at different power levels. Frequency spectra were prepared by performing Fast Fourier Transformation of the recorded time domain waveforms. The frequency spectra were used to obtain the first three harmonic amplitudes. The captured harmonic amplitudes were used to calculate the second and third harmonic ratios. Comparison of the harmonic ratios has shown the extraordinary sensitivity of the non-linear ultrasonic method, used in this study, to early damage detection. It was also observed that this sensitivity further increases as water cement ratio increases.

Non-destructive evaluation of concrete in damaged and undamaged states

This paper presents findings on nonlinear ultrasonic testing of concrete. The study was focused on testing cubic concrete specimens. It consisted of the non-destructive evaluation of concrete cubes using nonlinear ultrasonic technique with different frequency transducers. Concrete cubes of 150 mm × 150 mm × 150 mm in size and three distinct w/c 40%, 50%, and 60% were examined in damaged and undamaged states. Prior to inducing damages, the concrete cubes were ultrasonically evaluated in undamaged conditions. The damages were induced into the concrete cubes under compression testing. The transducer used at the wave-transmitting end had a broadband frequency of 100 kHz. However, at the receiving end, transducers of 200 and 300 kHz broadband frequency were used. The test results obtained for each concrete cube, in both damaged and undamaged conditions, were plotted and compared. The ratios of harmonic generations, nonlinear material parameters, and attenuation or loss in fundamental amplitude were calculated. The performance obtained by using transducers with different frequency as receivers in measuring the higher harmonics was also examined. The nonlinear ultrasonic test method using low frequency transducer as receiver exhibited greater sensitivity over high frequency transducer. Similarly, the third harmonic ratio was found more sensitive to concrete cracking than the second harmonic ratio. As concrete is a high attenuation material, the change in fundamental amplitude or attenuation was also found sensitive to using transducers with different frequency. The test results were also analyzed to find correlation between w/c, wave attenuation and higher harmonic generation based nonlinear parameters. These findings are very helpful for understanding the behavior of damaged concrete sections under nonlinear ultrasound testing.

NDT of Reinforcement Corrosion Using Ultrasonic Spectroscopy

Corrosion of built-in steel reinforcement ranks among the most serious mechanisms of bridge structure degradation. There are many reasons for the corrosion to occur: failures occurring during the bridge construction, consequences of traffic load, or, simple, ageing of the structures. Visual inspection of a bridge provides general information on the bridge condition. However, it cannot provide any information on the internal structure and integrity of the reinforced concrete or pre-loaded elements of the bridge in question. This is why non-destructive diagnostic methods are acquiring growing importance, helping researchers to properly evaluate the condition of a bridge and decide upon the most convenient methods for maintenance, repair or refurbishment of the bridge in question or its parts and schedule them accordingly.In this domain, methods employing the non-linear acoustic spectroscopy (NEWS - Nonlinear Elastic Wave Spectroscopy) achieved rush advancement recently. They are based on the fact that a non-linearity, which is due to the presence of a defect, makes an extraordinary indicator of the structure damage. These new, non-destructive methods appear to be promising for application to a wide range of materials featuring relatively heavy non-homogeneities, and for a large span of sites, from micro-chip to bridge structures. The present paper deals with an experimental study of the application of non-linear ultrasonic spectroscopy methods to the detection of steel reinforcement corrosion and its consequences for reinforced concrete specimens subjected to corrosion induced degradation cycles.

Detecting Damage in Composite Material Using Nonlinear Elastic Wave Spectroscopy Methods

Modern aerospace structures make increasing use of fibre reinforced plastic composites, due to their high specific mechanical properties. However, due to their brittleness, low velocity impact can cause delaminations beneath the surface, while the surface may appear to be undamaged upon visual inspection. Such damage is called barely visible impact damage (BVID). Such internal damages lead to significant reduction in local strengths and ultimately could lead to catastrophic failures. It is therefore important to detect and monitor damages in high loaded composite components to receive an early warning for a well timed maintenance of the aircraft. Non-linear ultrasonic spectroscopy methods are promising damage detection and material characterization tools. In this paper, two different non-linear elastic wave spectroscopy (NEWS) methods are presented: single mode nonlinear resonance ultrasound (NRUS) and nonlinear wave modulation technique (NWMS). The NEWS methods were applied to detect delamination damage due to low velocity impact (<12 J) on various composite plates. The results showed that the proposed methodology appear to be highly sensitive to the presence of damage with very promising future NDT and structural health monitoring applications.