It was recently discovered that inclusions and other types of inhomogeneities can be nondestructively detected by thermoelectric measurements in an entirely non-contact way by using high-sensitivity magnetometers to sense the weak thermoelectric currents around the affected region when the specimen is subjected to directional heating or cooling. This paper presents theoretical models capable of predicting the magnetic field produced by thermoelectric currents around inclusions under external thermal excitation. We investigated how the magnetic signal to be detected depends on (i) the relevant physical properties of the host and the inclusion, (ii) the size of the inclusion, (iii) the polarization of the magnetometer, (iv) the lift-off distance of the magnetometer from the specimen, and the (v) direction and (vi) strength of the external heating or cooling applied to the specimen. The presented analytical model is numerically evaluated for comparison to experimental results that were obtained by measuring the magnetic field produced by thermoelectric currents around surface-breaking spherical tin inclusions in copper under external thermal excitation for different lift-off distances between the sensor and the surface of the specimen. The diameter of the inclusions and the lift-off distance varied from 2.4 to 12.7 mm and from 12 to 20 mm, respectively. A fairly modest 0.7 °C/cm temperature gradient in the specimen produced peak magnetic flux densities ranging from 1 to 250 nT, that could be easily measured by a commercial fluxgate magnetometer. The experimental results were found to be in very good agreement with our analytical predictions.
{"title":"On the Exploitation of Thermoelectric Coupling for Characterization of Inclusions in Metals","authors":"A. Nayfeh, H. Carreon, P. Nagy","doi":"10.1063/1.1373956","DOIUrl":"https://doi.org/10.1063/1.1373956","url":null,"abstract":"\u0000 It was recently discovered that inclusions and other types of inhomogeneities can be nondestructively detected by thermoelectric measurements in an entirely non-contact way by using high-sensitivity magnetometers to sense the weak thermoelectric currents around the affected region when the specimen is subjected to directional heating or cooling. This paper presents theoretical models capable of predicting the magnetic field produced by thermoelectric currents around inclusions under external thermal excitation. We investigated how the magnetic signal to be detected depends on (i) the relevant physical properties of the host and the inclusion, (ii) the size of the inclusion, (iii) the polarization of the magnetometer, (iv) the lift-off distance of the magnetometer from the specimen, and the (v) direction and (vi) strength of the external heating or cooling applied to the specimen. The presented analytical model is numerically evaluated for comparison to experimental results that were obtained by measuring the magnetic field produced by thermoelectric currents around surface-breaking spherical tin inclusions in copper under external thermal excitation for different lift-off distances between the sensor and the surface of the specimen. The diameter of the inclusions and the lift-off distance varied from 2.4 to 12.7 mm and from 12 to 20 mm, respectively. A fairly modest 0.7 °C/cm temperature gradient in the specimen produced peak magnetic flux densities ranging from 1 to 250 nT, that could be easily measured by a commercial fluxgate magnetometer. The experimental results were found to be in very good agreement with our analytical predictions.","PeriodicalId":110638,"journal":{"name":"Nondestructive Evaluation and Characterization of Engineering Materials for Reliability and Durability Predictions","volume":"36 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114765639","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Shot peening is widely used in the aerospace and other industries to increase the damage tolerance of metal parts via producing a thin surface layer of compressive residual stress that prevents crack initiation and retards crack growth during service. Nondestructive evaluation of the prevailing compressive residual stress in the shallow subsurface layer is complicated by the adverse effects of shot peening, such as surface roughness and cold work that manifests itself through increased dislocation density and localized texture. Recent research efforts have revealed that conventional ultrasonic and eddy current NDT methods are simply too sensitive to surface roughness to quantitatively assess the subtle variations in mechanical and electrical properties that are caused by shot peening. On the other hand, noncontacting thermoelectric techniques are very unique among all other methods used in nondestructive materials characterization in that they are solely sensitive to intrinsic material variations regardless of the size, shape, and surface quality of the specimen to be tested. Noncontacting thermoelectric methods, based on magnetic detection of local thermoelectric currents around inhomogeneities in metals when a temperature gradient is established throughout the specimen, are especially well suited for the characterization of shot peened surfaces. Experimental evidence suggests that this method can reliably detect and quantitatively assess otherwise hidden variations in material properties within the shallow surface layer of shot peened specimens. The thermoelectric method is sensitive to all three “material” effects of shot peening, namely residual stress, local texture, and increased dislocation density, but it is entirely insensitive to its “geometrical” by-product, i.e., the rough surface topography. Further development of the thermoelectric method is necessary to study the underlying physical phenomena before it can be successfully adapted to practical inspection problems, but the preliminary results presented in this paper are very promising.
{"title":"Characterization of Shot-Peened Surfaces by a Noncontacting Thermoelectric Method","authors":"H. Carreón, P. Nagy","doi":"10.1115/imece2000-1644","DOIUrl":"https://doi.org/10.1115/imece2000-1644","url":null,"abstract":"\u0000 Shot peening is widely used in the aerospace and other industries to increase the damage tolerance of metal parts via producing a thin surface layer of compressive residual stress that prevents crack initiation and retards crack growth during service. Nondestructive evaluation of the prevailing compressive residual stress in the shallow subsurface layer is complicated by the adverse effects of shot peening, such as surface roughness and cold work that manifests itself through increased dislocation density and localized texture. Recent research efforts have revealed that conventional ultrasonic and eddy current NDT methods are simply too sensitive to surface roughness to quantitatively assess the subtle variations in mechanical and electrical properties that are caused by shot peening. On the other hand, noncontacting thermoelectric techniques are very unique among all other methods used in nondestructive materials characterization in that they are solely sensitive to intrinsic material variations regardless of the size, shape, and surface quality of the specimen to be tested. Noncontacting thermoelectric methods, based on magnetic detection of local thermoelectric currents around inhomogeneities in metals when a temperature gradient is established throughout the specimen, are especially well suited for the characterization of shot peened surfaces. Experimental evidence suggests that this method can reliably detect and quantitatively assess otherwise hidden variations in material properties within the shallow surface layer of shot peened specimens. The thermoelectric method is sensitive to all three “material” effects of shot peening, namely residual stress, local texture, and increased dislocation density, but it is entirely insensitive to its “geometrical” by-product, i.e., the rough surface topography. Further development of the thermoelectric method is necessary to study the underlying physical phenomena before it can be successfully adapted to practical inspection problems, but the preliminary results presented in this paper are very promising.","PeriodicalId":110638,"journal":{"name":"Nondestructive Evaluation and Characterization of Engineering Materials for Reliability and Durability Predictions","volume":"159 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122171209","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The feasibility of detecting interface degradation and separation of steel rebars in concrete beams using Lamb waves is investigated in this paper. It is shown that Lamb waves can easily detect these defects. A special coupler between the steel rebar and ultrasonic transducers has been used to launch non-axisymmetric guided waves in the steel rebar. This investigation shows that the Lamb wave inspection technique is an efficient and effective tool for health monitoring of reinforced concrete structures because the Lamb wave can propagate a long distance along the reinforcing steel bars embedded in concrete as the guided wave and is sensitive to the interface debonding between the steel rebar and concrete.
{"title":"Inspection of Concrete-Metal Rod Interface Using Guided Waves","authors":"W. Na, T. Kundu, M. Ehsani","doi":"10.1115/imece2000-1647","DOIUrl":"https://doi.org/10.1115/imece2000-1647","url":null,"abstract":"\u0000 The feasibility of detecting interface degradation and separation of steel rebars in concrete beams using Lamb waves is investigated in this paper. It is shown that Lamb waves can easily detect these defects. A special coupler between the steel rebar and ultrasonic transducers has been used to launch non-axisymmetric guided waves in the steel rebar. This investigation shows that the Lamb wave inspection technique is an efficient and effective tool for health monitoring of reinforced concrete structures because the Lamb wave can propagate a long distance along the reinforcing steel bars embedded in concrete as the guided wave and is sensitive to the interface debonding between the steel rebar and concrete.","PeriodicalId":110638,"journal":{"name":"Nondestructive Evaluation and Characterization of Engineering Materials for Reliability and Durability Predictions","volume":"79 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126314793","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Patrick J. Sincebaugh, J. Sandhu, Honghui Wang, W. J. Popek
The objective of this paper is to provide details on the development of a novel acousto-optic sensor that can be utilized to nondestructively evaluate materials and components in near real-time. The acousto-optic sensor, which is the basis for Acoustography, provides wide-area, near real-time ultrasonic attenuation maps that can be analyzed to detect anomalies such as cracks, delaminations, and porosity. Details on applying Acoustography to inspect complex shaped parts will be provided. Future work in the area of Acoustography will also be presented.
{"title":"Acousto-Optic Sensors for Real-Time, Wide-Area Inspection of Advanced Materials and Components","authors":"Patrick J. Sincebaugh, J. Sandhu, Honghui Wang, W. J. Popek","doi":"10.1115/imece2000-1645","DOIUrl":"https://doi.org/10.1115/imece2000-1645","url":null,"abstract":"\u0000 The objective of this paper is to provide details on the development of a novel acousto-optic sensor that can be utilized to nondestructively evaluate materials and components in near real-time. The acousto-optic sensor, which is the basis for Acoustography, provides wide-area, near real-time ultrasonic attenuation maps that can be analyzed to detect anomalies such as cracks, delaminations, and porosity. Details on applying Acoustography to inspect complex shaped parts will be provided. Future work in the area of Acoustography will also be presented.","PeriodicalId":110638,"journal":{"name":"Nondestructive Evaluation and Characterization of Engineering Materials for Reliability and Durability Predictions","volume":"63 8 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128726278","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The interaction of surface acoustic waves with finite-size, surface-breaking, semi-circular cracks is studied theoretically, numerically, and experimentally. We focus on the behavior of the reflection coefficient of the Rayleigh wave from such cracks in both the far and near fields of the crack. It is shown that, in the near field, the reflection coefficient from such cracks is higher than the reflection coefficient measured in the far field. This is mainly due to the diverging nature of the Rayleigh wave reflected from the crack. In the high crack depth to wave length ratio, the finite element and experimental results approach the limiting value of the reflection coefficient from a 90-degree corner.
{"title":"Analysis of the Reflection Coefficient of Rayleigh Waves From Surface-Breaking Cracks","authors":"W. Hassan, W. Veronesi","doi":"10.1115/imece2000-1642","DOIUrl":"https://doi.org/10.1115/imece2000-1642","url":null,"abstract":"\u0000 The interaction of surface acoustic waves with finite-size, surface-breaking, semi-circular cracks is studied theoretically, numerically, and experimentally. We focus on the behavior of the reflection coefficient of the Rayleigh wave from such cracks in both the far and near fields of the crack. It is shown that, in the near field, the reflection coefficient from such cracks is higher than the reflection coefficient measured in the far field. This is mainly due to the diverging nature of the Rayleigh wave reflected from the crack. In the high crack depth to wave length ratio, the finite element and experimental results approach the limiting value of the reflection coefficient from a 90-degree corner.","PeriodicalId":110638,"journal":{"name":"Nondestructive Evaluation and Characterization of Engineering Materials for Reliability and Durability Predictions","volume":"20 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114589459","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The elastic wave generation and the efficiency of the thermal-to-mechanical energy conversion process of elastic wave generation by laser excitation are studied. A previously developed transfer matrix formulation [3, 4] is reviewed and the transient response in a silicon layer is computed by employing FFT. The transient thermal and mechanical response of a layer are considered, and the transient temperature, stress, acceleration and mechanical power are obtained under micro-second level excitation. The generation efficiency for the elastic wave components, which are utilized to evaluate the state of layered structures, is examined for a silicon layer. The results presented are useful in determining instrument specification, such as laser power, receiver dynamic range, and test set-up design.
{"title":"An Efficiency Study of Laser-Induced Thermoelastic Wave Generation in Layers","authors":"Ji Wu, C. Cetinkaya, Chen Li","doi":"10.1115/imece2000-1646","DOIUrl":"https://doi.org/10.1115/imece2000-1646","url":null,"abstract":"\u0000 The elastic wave generation and the efficiency of the thermal-to-mechanical energy conversion process of elastic wave generation by laser excitation are studied. A previously developed transfer matrix formulation [3, 4] is reviewed and the transient response in a silicon layer is computed by employing FFT. The transient thermal and mechanical response of a layer are considered, and the transient temperature, stress, acceleration and mechanical power are obtained under micro-second level excitation. The generation efficiency for the elastic wave components, which are utilized to evaluate the state of layered structures, is examined for a silicon layer. The results presented are useful in determining instrument specification, such as laser power, receiver dynamic range, and test set-up design.","PeriodicalId":110638,"journal":{"name":"Nondestructive Evaluation and Characterization of Engineering Materials for Reliability and Durability Predictions","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126080103","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Characterization of animal bones by acoustic microscopy is a relatively new field of research. Non-uniformity of bones requires a complete analysis of the interaction between the focused acoustic beam and the bone specimens for its characterization. The complete analysis produces the V(z) curve taking into account the lens angle and the elastic properties of the bone. V(z) oscillations may be generated by surface skimming Rayleigh waves and/or P-waves in different parts of the bone depending on the bone properties. In this paper after a short review of different applications of the acoustic microscopy technique a complete theory of the V(z) curve synthesis is briefly presented. A number of V(z) curves are analytically generated following this theory. These curves sometimes show a regular oscillatory shape as predicted by the simple ray theory. However, often the synthesized V(z) curves show irregularities. The synthesized V(z) curve for silicon has been compared with the experimental results to have a confidence on the analytical computation. Then additional numerical exercises are carried out to understand why sometimes the V(z) curve shapes are irregular, and whether the P-wave speed and/or the Rayleigh wave speed of the material can be extracted from such irregular shaped V(z) curves. After understanding the V(z) phenomenon the wave speeds at different points of a bone are experimentally measured from its V(z) curves.
{"title":"Acoustic Microscopy for Bone Characterization","authors":"T. Kundu, C. Jørgensen","doi":"10.1115/imece2000-1643","DOIUrl":"https://doi.org/10.1115/imece2000-1643","url":null,"abstract":"\u0000 Characterization of animal bones by acoustic microscopy is a relatively new field of research. Non-uniformity of bones requires a complete analysis of the interaction between the focused acoustic beam and the bone specimens for its characterization. The complete analysis produces the V(z) curve taking into account the lens angle and the elastic properties of the bone. V(z) oscillations may be generated by surface skimming Rayleigh waves and/or P-waves in different parts of the bone depending on the bone properties. In this paper after a short review of different applications of the acoustic microscopy technique a complete theory of the V(z) curve synthesis is briefly presented. A number of V(z) curves are analytically generated following this theory. These curves sometimes show a regular oscillatory shape as predicted by the simple ray theory. However, often the synthesized V(z) curves show irregularities. The synthesized V(z) curve for silicon has been compared with the experimental results to have a confidence on the analytical computation. Then additional numerical exercises are carried out to understand why sometimes the V(z) curve shapes are irregular, and whether the P-wave speed and/or the Rayleigh wave speed of the material can be extracted from such irregular shaped V(z) curves. After understanding the V(z) phenomenon the wave speeds at different points of a bone are experimentally measured from its V(z) curves.","PeriodicalId":110638,"journal":{"name":"Nondestructive Evaluation and Characterization of Engineering Materials for Reliability and Durability Predictions","volume":"95 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124621547","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Exact and approximate analyses of ultrasonic guided wave propagation in thin orthotropic layers are presented in this work. Exact solutions to the equations governing the dependence of guided wave propagation speeds on the elastic constants characterizing the anisotropic properties of the layers are presented and compared with the predictions of first order approximate theories for extensional and flexural waves in thin plates. Comparison with available experimental results for dispersion of these waves in thin sheets of different types of papers leads to the confirmation or modification of the elastic constants and density reported for these papers. A particular focus of this study is the coupling of three types of guided waves (extensional (S), flexural (A), and shear-horizontal (SH)) due to anisotropy of the material. It is shown that there are significant changes in the dispersion characteristics of these modes at certain frequencies, which can be exploited to measure the in-plane elastic properties of thin layers. Another focus is to study the limitations of approximate results when compared with exact solutions for wave propagation in different directions. In general good agreements are found at low frequencies.
{"title":"Ultrasonic Guided Waves in Thin Orthotropic Layers: Exact and Approximate Analyses","authors":"S. Datta, O. Mukdadi","doi":"10.1115/imece2000-1650","DOIUrl":"https://doi.org/10.1115/imece2000-1650","url":null,"abstract":"\u0000 Exact and approximate analyses of ultrasonic guided wave propagation in thin orthotropic layers are presented in this work. Exact solutions to the equations governing the dependence of guided wave propagation speeds on the elastic constants characterizing the anisotropic properties of the layers are presented and compared with the predictions of first order approximate theories for extensional and flexural waves in thin plates. Comparison with available experimental results for dispersion of these waves in thin sheets of different types of papers leads to the confirmation or modification of the elastic constants and density reported for these papers. A particular focus of this study is the coupling of three types of guided waves (extensional (S), flexural (A), and shear-horizontal (SH)) due to anisotropy of the material. It is shown that there are significant changes in the dispersion characteristics of these modes at certain frequencies, which can be exploited to measure the in-plane elastic properties of thin layers. Another focus is to study the limitations of approximate results when compared with exact solutions for wave propagation in different directions. In general good agreements are found at low frequencies.","PeriodicalId":110638,"journal":{"name":"Nondestructive Evaluation and Characterization of Engineering Materials for Reliability and Durability Predictions","volume":"9 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122263234","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The objective of this paper is to characterize the cure state of polymer adhesive joints using nonlinear ultrasonic techniques. To this end, through transmission tests were carried out on joint samples that had been subjected to various curing conditions. In these tests, a 40-cycle harmonic signal was generated by a 2MHz narrow-band PZT transducer as the incident wave. The wave transmitted through the adhesive joint was received with a 4MHz narrow-band PZT transducer. The magnitude of the second order harmonics in the transmitted signal was measured and the corresponding nonlinear parameter β was calculated. A fairly good correlation was observed between the nonlinear parameter and the cure state. It was found that under-curing (lower curing temperature or short curing time) tends to increase the nonlinear parameter.
{"title":"Effects of Cure State on the Ultrasonic Nonlinear Parameter in Adhesive Joints","authors":"Guoli Liu, J. Qu, L. Jacobs","doi":"10.1115/imece2000-1649","DOIUrl":"https://doi.org/10.1115/imece2000-1649","url":null,"abstract":"\u0000 The objective of this paper is to characterize the cure state of polymer adhesive joints using nonlinear ultrasonic techniques. To this end, through transmission tests were carried out on joint samples that had been subjected to various curing conditions. In these tests, a 40-cycle harmonic signal was generated by a 2MHz narrow-band PZT transducer as the incident wave. The wave transmitted through the adhesive joint was received with a 4MHz narrow-band PZT transducer. The magnitude of the second order harmonics in the transmitted signal was measured and the corresponding nonlinear parameter β was calculated. A fairly good correlation was observed between the nonlinear parameter and the cure state. It was found that under-curing (lower curing temperature or short curing time) tends to increase the nonlinear parameter.","PeriodicalId":110638,"journal":{"name":"Nondestructive Evaluation and Characterization of Engineering Materials for Reliability and Durability Predictions","volume":"14 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115469160","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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