Nonlinear Ultrasonic Spectroscopy Research Articles

Experimental Evaluation Method of Carbonation in Concrete Structure Using Nonlinear Resonant Ultrasonic Spectroscopy

Carbonation is a typical type of concrete deterioration that can cause various physicochemical changes and adversely affects the performance of reinforced concrete structures, particularly in offshore structures. Nonlinear resonant ultrasonic spectroscopy (NRUS), which is a non-destructive test technique, is applied in this study to experimentally evaluate the degree of concrete carbonation without damaging the structure. Nonlinearity parameters of test specimens exposed to accelerated carbonation conditions are measured via NRUS. The measured nonlinearity parameters indicate lower values for longer carbonation durations. This is because internal microcracks are reduced by CaCO<sub>3</sub>, which is a carbonation product. The consistent trend of the experimental results shows that NRUS can be effectively applied to evaluate concrete carbonation.

Toward In-situ Characterization of Additively Manufactured Parts Using Nonlinear Resonance Ultrasonic Spectroscopy

ABSTRACT In this study, we investigate the feasibility of using nonlinear resonance ultrasound spectroscopy (NRUS) for in-situ monitoring of additively manufactured (AM) parts i.e., while they are still on the build plate. In NRUS, the test specimen is excited around one or more of its resonance frequencies with increasing driving amplitude. The linear shift in resonance frequency with the increasing driving amplitude is a measure of the constituent material’s hysteretic nonlinearity (α), which is itself related to some degree of micro-damage in the test specimens. We conduct NRUS on test specimens glued to a thick plate. The specimens are excited using a piezoelectric transducer (PZT) adhered to the bottom of the plate. We use this setup to measure the hysteretic nonlinearity parameters ( and ) of several cylindrical AM specimens fabricated by laser powder bed fusion technique as well as a few non-AM metallic specimens. The measured nonlinearity parameters for the specimens on the build plate (process monitoring mode) are compared to those measured without the build plate (quality control mode). We observe a systematic decrease in the measured nonlinearity when the specimens are tested on the build plate. An analytical study demonstrates that we measure the weighted average nonlinearity of the specimen and build plate, which itself has a lower nonlinearity. Despite the observed difference, the measured nonlinearity parameters of the specimens with and without the build plate are highly correlated. With further investigations, the proposed test setup can potentially be used for characterization of AM parts in situ.

Influence of fast dynamics effects on resonant ultrasonic vibrations of polycrystalline metal rods

A theoretical model for the formation of ultrasonic signals in metallic microcrystalline rods taking into account the metastable behavior of their defective states is proposed. The influence of metastable states of the defective structure of samples on the features of changes in their resonant frequencies in ultrasonic experiments of fast dynamics is analyzed. The decrease in Young's modulus in such processes is explained. The correspondence between theoretical and experimental data is demonstrated for the example of resonant acoustic vibrations of rods made of aluminum alloy D16. Keywords: nonlinear resonant ultrasonic spectroscopy, defect structure, mechanical stresses, effects of fast and slow dynamics.

Nonlinear Resonant Ultrasonic Spectroscopy (NRUS) for Monitoring Fatigue Crack Growth in Aluminum

ABSTRACT Nonlinear resonant ultrasonic spectroscopy (NRUS) is a resonance-based acoustic testing technique that yields the hysteretic elastic nonlinearity parameter by measuring the resonance frequency shift with increasing driving amplitude. NRUS offers great potential for nondestructive evaluation since it is relatively simple to implement and can detect incipient damage thanks to the high sensitivity of hysteretic nonlinearity parameter to micro-damage. Previous research has shown that NRUS can monitor distributed damage in a wide variety of materials, but the application of NRUS for detection of local defects in metals is less explored. In this study, the feasibility of using NRUS to assess local progressive damage in aluminum is investigated. We use three-point bending fatigue test to initiate a single fatigue crack in a large aluminum specimen. The cyclic loading is interrupted at several stages in order to image the crack using Scanning Electron Microscopy (SEM) and to perform NRUS and other tests. As the crack grows in length, NRUS records a gradual increase in the resonance frequency shift. However, the trend for the amplitude dependency of resonance frequency shift is different from what has been previously reported in materials with distributed damage; the resonance frequency changes are larger at low strain than at high strains. In addition, the utility of multi-modal NRUS for locating the fatigue crack is demonstrated. Finally, we compare the results of NRUS and those from an impact-based NRUS (INRUS) that uses an automated impact hammer as the excitation source in differentiating the fatigue-damaged from the intact specimen. Our findings suggest the potential of NRUS and INRUS in detecting local damage in metals.

Nonlinear resonance ultrasonic spectroscopy (NRUS) for the quality control of additively manufactured samples

Additive manufacturing (AM) is becoming increasingly popular due to its ability to build parts with customer-designed complex geometries. However, the lack of established quality control/assurance practices for the built parts poses a challenge to a wider adoption of additive manufacturing by some industries. In this study, we investigate the utility of nonlinear resonance ultrasonic spectroscopy (NRUS) for predicting the fatigue life of cylindrical Ti–6Al–4V samples manufactured using powder bed fusion on the same build. We use NRUS to measure several linear and nonlinear parameters for the samples before and after hot isostatic pressing (HIPing). The samples are then fatigue tested. We report the correlation between NRUS parameters and fatigue life. Our findings suggest that resonance frequency, quality factor, and the hysteretic nonlinearity of the samples are correlated to their fatigue life. These correlations are promising because the measurements are obtained from distinct samples as opposed to collecting data on the same sample undergoing increasing fatigue cycles. This study suggests that NRUS has the potential to be used as a nondestructive evaluation (NDE) tool for AM part quality control.

Linear and nonlinear resonant ultrasonic techniques applied to assess delayed ettringite formation on concrete samples

This study investigates the application of different ultrasonic Non-Destructive tests to assess Delayed Ettringite Formation, in concrete samples exhibiting low kinetic expansions (and up to 0.21%). Linear and nonlinear Resonant Ultrasonic Spectroscopy and Acoustic Emission tests were used. Scanning Electron Microscopy and optical microscopy observations were conducted at the end of the monitoring tests. The results showed a slight increase of the dynamic modulus and Quality factor while nonlinear hysteretic parameters remained constant over the test duration. Acoustic Emission tests attested the occurrence of events. However, the microscopic observations did not reveal meaningful differences in microcracking extent between the samples.

Detection of Reinforced Concrete Thermal Damage by Nonlinear Ultrasonic Spectroscopy

Nonlinear Ultrasonic Spectroscopy (NUS) methods investigates nonlinear phenomena that occur when the sound or ultrasound waves pass through the material. This paper focuses on the use of these methods for nondestructive testing of reinforced concrete damaged by high temperature. For this research, reinforced concrete beams with one steel rod were made and the NUS measuring equipment was assembled. An appropriate nonlinear parameter was selected to assess the damage. The nonlinear behavior of thermally damaged reinforced concrete was manifested by the deformation of ultrasound waves passing through the measured samples, resulting in nonlinear effects in the frequency spectra of the recorded signal.

Non-linear Ultrasonic Spectroscopy of 3d Printed Metallic Samples

Non-linear Ultrasonic Spectroscopy of 3d Printed Metallic Samples

Experimental characterization of ultrasonic nonlinearity in concrete under cyclic change of prestressing force using Nonlinear Resonant Ultrasonic Spectroscopy

In this paper, an experimental study was conducted to investigate the effect of varying prestressing force on the nonlinearity of concrete. Prestressed concrete beams, which have been rarely studied in terms of ultrasonic nonlinearity, were prepared. When the prestressing force changes, the stress condition of the concrete inside the beam is affected. This leads to the generation of micro-cracks and a change of the mechanical properties, and as such it is necessary to introduce a nonlinear ultrasonic technique that sensitively reflects microstructural change. In the experiment, a repetitive prestressing load history, which includes maximum levels of 45%, 60%, and 75% based on the compressive strength, was designed to evaluate the effects of repetitive loading and different levels of loading on the nonlinearity. A comparison with the measured results of the linear ultrasonic method was also carried out to verify the stress-dependent change of nonlinearity induced by external loads. With the experimental results, the adopted technique is found to be more sensitive to damage then conventionally used ultrasonic method. As the investigation of the methodology is effective in prestressed concrete structures, the possibility of ultrasonic nonlinearity as an indicator of prestressing force is evaluated.

Adoption of Nonlinear Resonant Ultrasonic Spectroscopy for the Evaluation of Stress State on Concrete in Prestressed Beam

프리스트레스트 보의 인장력 변화에 따른 콘크리트 응력 수준을 평가하기 위하여, 초음파를 이용하는 기존의 방법보다 개 선된 비선형 초음파 공진 기법의 도입을 제안하였다. 이는 동일하게 초음파를 사용하는 선형의 기법보다 월등히 높은 민감 도를 보이므로 초기 상태의 응력 평가에도 유리하다. 비선형 초음파 공진 기법은 초음파 통과시 매질 상태에 따른 공진 주파 수의 변화의 정도로부터 계산되는 비선형 인자의 값을 측정하며, 측정 결과는 콘크리트의 응력 상태와도 밀접한 연관을 갖 는다. 본 연구에서는 유압 펌프를 통한 인장력 작용에 따른 비선형 인자의 측정을 수행함으로써 두 인자 사이에 밀접한 연관 성이 있음을 확인하고, 반복적인 하중 이력의 작용이 비선형 인자의 변화에 미치는 영향을 분석하였다. 추가적으로, 선형 초 음파 전파 속도 측정 결과를 비교하여 제안한 방법의 민감도를 검증하였다. 측정 결과를 통해 프리스트레스트 보의 콘크리 트 응력 수준 평가를 위한 비선형 초음파 공진 기법의 적용 가능성을 확인하였다.

Možnosti metod NUS in Udarec-odmev za kontrolo korozije jekla v betonu

The corrosion of steel elements in reinforced concrete can cause considerable damage to civil-engineering structures. Early detection of rust is therefore very important. The aim of this paper is to evaluate the possibility of using nonlinear ultrasonic spectroscopy with a single exciting harmonic frequency and the impact-echo method for monitoring the corrosion of concrete-covered steel. For the research we manufactured concrete beams, reinforced with a standard reinforcing-steel bar passing through their centre. After concrete curing and drying, the samples were exposed to a 20 % carbon dioxide atmosphere. After the concrete pH decreased below 9.6 throughout the sample volume, the samples were immersed into a 5 % water solution of NaCl and subsequently placed into a drying oven. Measurements were carried out before the carbonation of the concrete, after it, and then after every 20th cycle of the accelerated degradation by chlorides. Nonlinear-ultrasonic-spectroscopy (NUS) methods are based on the fact that crack-induced nonlinearity makes a sensitive material-impairment indicator. The impact-echo method uses short-time mechanical impulses applied to the surface of a test sample, producing elastic waves. These waves spread throughout the sample and reflect from the surface but also from the microcracks and unobservable defects inside the sample. To verify the correctness of the NUS and impact-echo-method results, additional measurements were carried out (a confocal scanning microscope). It was proved that both methods could be used for monitoring the corrosion of concrete-covered steel.

Concrete Carbonation Monitoring by Nonlinear Ultrasonic Spectroscopy

The aim of this paper is to evaluate the possibility of using the nonlinear ultrasonic spectroscopy with a single exciting harmonic frequency for concrete carbonation monitoring. Carbonation of concrete is related with the corrosion of steel reinforcement and with carbonation shrinkage. Due to the conditions in the laboratory were as close as possible to practical terms, we used reinforced concrete samples. For the research, the concrete beams with one standard reinforcing bar passing through the centre of the sample were made. Prepared samples were exposed to an atmosphere with increased carbon dioxide content. The measurements using the nonlinear ultrasonic spectroscopy with a single exciting harmonic frequency were realized before and after carbonation of concrete.

Application of Nonlinear Ultrasonic Method for Monitoring of Stress State in Concrete

As the lifespan of concrete structures increases, their load carrying capacity decreases owing to cyclic loads and long-term effects such as creep and shrinkage. For these reasons, there is a necessity for stress state monitoring of concrete members. Particularly, it is necessary to evaluate the concrete structures for behavioral changes by using a technique that can overcome the measuring limitations of usual ultrasonic nondestructive evaluation methods. This paper proposes the use of a nonlinear ultrasonic method, namely, nonlinear resonant ultrasonic spectroscopy (NRUS) for the measurement of nonlinearity parameters for stress monitoring. An experiment compared the use of NRUS method and a linear ultrasonic method, namely, ultrasonic pulse velocity (UPV) to study the effects of continuously increasing loads and cyclic loads on the nonlinearity parameter. Both NRUS and UPV methods found a similar direct relationship between load level and that parameter. The NRUS method showed a higher sensitivity to micro-structural changes of concrete than UPV method. Thus, the experiment confirms the possibility of using the nonlinear ultrasonic method for stress state monitoring of concrete members.

The Application of NUS Method for Concrete-Covered Steel Corrosion Monitoring

The corrosion of steel elements in reinforced concrete can cause considerable damage to civil engineering structures. Early detection of corrosion is therefore very important. Steel in concrete is protected if the concrete pH is higher than 9.6. Carbonated concrete, unfortunately, has a lower pH and this causes that the unprotected steel reinforcement begins to corrode. Nonlinear ultrasonic spectroscopy (NUS) methods shows potential to be very reliable to identify the structure defects in a wide range of materials. These methods are based on the fact that crack-induced nonlinearity makes a sensitive material impairment indicator. This paper describes the ability of one of NUS methods for monitoring steel corrosion in reinforced concrete. It studies nonlinear interaction between elastic waves and structural defects caused by corrosion of steel in concrete. For research we used concrete beams with ten millimetres thick steel rods. These beams were exposed to accelerated degradation by chlorides. The paper presents the initial results of our research.

Structural Integrity of Stone Blocks From Charles Bridge in Prague

ABSTRACTThe Charles Bridge is the oldest, still-standing gothic bridge that crosses the Vltava River in Prague and up to now has belonged among the most sought-after historical monuments in the Czech Republic. The bridge has been repeatedly damaged due to floods and has been repaired several times. In the reconstructions, damaged sandstone blocks were substituted in facing. This experimental study focused on nonlinear ultrasonic spectroscopy for testing stone blocks that were extracted from the historical bridge structure. The objective of these experiments was verifying whether the methods can be applied to evaluating the internal structure of blocks, which are built-in in the structure in situ. Intact-structure blocks, blocks that had been repaired in the past, and damaged-structure blocks were measured. Two methods of nonlinear ultrasonic spectroscopy were applied—the method with single harmonic ultrasonic signal and with two harmonic ultrasonic signals. Measurement results of both applied methods proved resulting parameters correlation with block structure integrity quality.

A set of measures for the systematic classification of the nonlinear elastic behavior of disparate rocks

AbstractDynamic acoustoelastic testing is performed on a set of six rock samples (four sandstones, one soapstone, and one granite). From these studies at 20 strain levels 10−7<ϵ<10−5, four measures characterizing the nonlinear elastic response of each sample are found. Additionally, each sample is tested with nonlinear resonant ultrasonic spectroscopy and a fifth measure of nonlinear elastic response is found. These five measures of the nonlinear elastic response of the samples (approximately 3 × 6×20 × 5 numbers as each measurement is repeated 3 times) are subjected to careful analysis using model‐independent statistical methods, principal component analysis, and fuzzy clustering. This analysis reveals differences among the samples and differences among the nonlinear measures. Four of the nonlinear measures are sensing much the same physical mechanism in the samples. The fifth is seeing something different. This is the case for all samples. Although the same physical mechanisms (two) are operating in all samples, there are distinctive features in the way the physical mechanisms present themselves from sample to sample. This suggests classification of the samples into two groups. The numbers in this study and the classification of the measures/samples constitute an empirical characterization of rock nonlinear elastic properties that can serve as a valuable testing ground for physically based theories that relate rock nonlinear elastic properties to microscopic elastic features.

Application acoustic emission method during concrete frost resistance

Frost resistance is one of the most frequent characteristics of concrete. It is a very complex subject and the test methods themselves are still in development and the international consensus on methodology is still sought, too. The determination concrete frost resistance takes several weeks, months or even more than a year. However micro-structural changes as micro-cracks have not been described sufficiently. Acoustic Emission Method as unusual Non-Destructive Methods can help to monitor structural changes during common frost resistance measuring. Note the Acoustic Emission Method detects only active “defects” into monitored structure. Thus when e.g. crack grows some acoustic waves spread from crack place, i. e. from acoustic emission source. The method does not detect geometric discontinuities and “passive” defects. Selected Non-Destructive Methods as Ultrasound, Non-Linear Ultrasonic Spectroscopy, Impact Echo etc. are used to confirm micro-structural changes. The article describes the first experiment with its imperfections, difficulties and possibilities.

Monitoring of the Damage in Stone Blocks by Means of Non-Destructive Methods

This paper deals with the damage assessment in stone blocks dismantled from a historic bridge construction. Nonlinear ultrasonic spectroscopy and impact echo methods were used for evaluating the stone block integrity structure. Harmonic analysis of the sample response on well defined ultrasonic excitation was used in the case of nonlinear ultrasonic method application. The amplitude dependent spectral changes of the probing signals were measured in the damaged blocks. Measurement results showed that the analysis of amplitude dependent spectral changes is a promising method for the damage assessment in structures. The Impact-Echo method is a technique for detecting defects in material structure such as stone blocks. It is based on monitoring the propagation of elastic waves from a short-duration mechanical impact. The aim of this paper is to provide an overview of the technique and to discuss the important parameters involved in this type of testing. The impact echo method is used to generate low-frequency stress waves from 500 Hz to 50 kHz that propagate into the structure and are reflected by defects and external surfaces.

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.

Numerical investigation of innovative nonlinear ultrasonic spectroscopy for detection and sizing interface defects in composites

The article is devoted to innovative nonlinear acoustic techniques of non-destructive testing (NDT) of composites. Modern composites have a very complex inhomogeneous structure with a large number of interface bond-lines. Along these bond-lines there are interface defects, such as delaminations, microcracks, debonding and weakening of adhesive bonds. This leads to the necessity of distinguishing from each other a signal from given defects and a signal from interface bond-lines. The task becomes more complicated because interface defects have a very small thickness of micro or even nanoscopic scale. Conventional techniques of ultrasonic testing have a very low sensitivity of these defects detection. The article describes a novel acoustic-mechanical approach to numerical modeling of nonlinear acoustic interaction of ultrasonic wave with interface defect. The results of computer simulation of this nonlinear acoustic interaction are analyzed. A simple technique of nonlinear ultrasonic spectroscopy is suggested for detecting and sizing the interface defects. http://dx.doi.org/10.5755/j01.u.66.2.528