Effect of grain size distribution on the acoustic nonlinearity parameter

Abstract: Grain size is an important parameter in evaluating the properties of microstructures in metals. In this paper, the attenuation coefficient of Rayleigh waves is introduced to characterize grain size in heat treated 316L stainless steel. Rayleigh wave attenuation is measured using an angle beam wedge transducer as the transmitter and an air-coupled transducer as the receiver. The results show that the grain size in 316L stainless steel increases due to heat treatment time, the hardness decreases accordingly, and the attenuation coefficient of Rayleigh waves increases. This indicates that the Rayleigh wave attenuation is sufficient in distinguishing the changes in the properties of the heat-treated stainless steel. It is found that compared with the measurement method using an angle beam wedge receiver, the measured results are efficient, more stable and less influenced by the surface state when an air-coupled receiver is used. In addition, comparison results also show that the Rayleigh wave attenuation is more sensitive to changes in material properties than the longitudinal wave attenuation, as the wavelength of the Rayleigh wave is shorter than that of the longitudinal wave at the same frequency.

Abstract: In the present study, Rayleigh waves are propagated through a thick Aluminum (Al) plate to evaluate its material nonlinearity based on the second harmonic produced in the response. The experiments and numerical simulations are carried out on the pristine and fatigued thick Al specimens, and an amplitude-based Rayleigh wave nonlinear parameter is used to characterize the material nonlinearity. In addition, a physics-based nonlinear parameter that depends on the sub-structural evolution parameters, and higher-order plastic and elastic constants are also used to characterize the nonlinearity of the pristine and fatigued Al material. They found to be in good agreement for the predefined conditions of tone burst cycles in the actuation signal and propagation distance. The knowledge of material nonlinearity parameters evaluated for the pristine and fatigued thick plate specimens using Rayleigh waves is shown in the present study to be crucial to evaluate the remnant useful life (RUL) of the fatigued specimen with fair accuracy.

Abstract: The Review of Progress in Quantitative NDE is the world's leading conference in reporting annually new research and development results in quantitative NDE. The conference reports on both fundamental and applied advances in NDE and promotes communication between the research and engineering communities and emphasize current reporting of work in progress. Attendees include representatives of academia (including students), industry, and government with approximately one-half coming from the United States and the other half from overseas. This volume represents the best report of ongoing work that is available anywhere. Connections and overlap with the medical diagnostic community are highlighted.

Abstract: The ultimate strength of most structural materials is mainly limited by the presence of microscopic imperfections serving as nuclei of the fracture process. Since these nuclei are considerably shorter than the acoustic wavelength at the frequencies normally used in ultrasonic nondestructive evaluation (NDE), linear acoustic characteristics are not sufficiently sensitive to this kind of microscopic degradation of the material's integrity. On the other hand, even very small imperfections can produce very significant excess nonlinearity which can be orders of magnitude higher than the intrinsic nonlinearity of the intact material. The excess nonlinearity is produced mainly by the strong local nonlinearity of microcracks whose opening is smaller than the particle displacement. Parametric modulation via crack-closure significantly increases the stress-dependence of fatigued materials. A special experimental technique was introduced to measure the second-order acousto-elastic coefficient in a great variety of materials including plastics, metals, composites and adhesives. Experimental results are presented to illustrate that the nonlinear acoustic parameters are earlier and more sensitive indicators of fatigue damage than their linear counterparts.

Abstract: We have developed a unified approach to solve for the attenuation and phase velocity variations of elastic waves in single‐phase, polycrystalline media due to scattering. Our approach is a perturbation method applicable for any material whose single‐crystal anisotropy is not large, regardless of texture, grain elongation, or multiple scattering. It accurately accounts for the anisotropy of the individual grains. It is valid for time‐harmonic waves with all ratios of grain size to wavelength. It uses an autocorrelation function to characterize the geometry of the grains, and thereby avoids coherent artifacts that occur if the grains are assumed to have symmetrical shapes and suggests new methods for characterizing distributions of grains that are irregularly shaped. We have carried out numerical calculations for materials that are untextured and equiaxed, and have cubic‐symmetry grains and an inverse exponential spatial autocorrelation function. These calculations agree with the previous calculations which are valid in the Rayleigh, stochastic, and geometric regions, and show the transitions between these regions. The complex transition between the Rayleigh and stochastic regions for longitudinal waves, and the severe limitations of the stochastic region for grains with fairly large anisotropy are of particular interest.

Abstract: Mechanics of Elastic Waves and Ultrasonic NDE T. Kundu, University of Arizona, USA Modeling of Ultrasonic Field by Distributed Point Source Method D. Placko, Ecole Normale Superieure, Cachan, France T. Kundu, University of Arizona, USA Ultrasonic Systems for Industrial NDE D. Bray, Don E. Bray, Inc, USA Guided Waves for Plate Inspection T. Kundu, University of Arizona, USA Cylindrical Waveguides and Their Applications in Ultrasonic Evaluation J. Qu and L. Jacobs, Georgia Institute of Technology, USA Fundamentals and Applications of Nonlinear Ultrasonic NDE J. Cantrell, NASA Langely Research Center, USA Theory and Applications of Laser-Ultrasonic Techniques S. Krishnaswami, Northwestern University, USA Electro-Magnetic Acoustic Transducers: EMATS B. Maxfield, Industrial Sensors and Actuators, USA Ultrasonic NDE for Structural Health Monitoring: Built-In Diagnostics for Hot Spot Monitoring in Metallic and Composite Structures J.-B. Ihn and F. K. Chang, Stanford University, USA, Brillouin Scattering Measurement of SAW Velocities for Determining Near-surface Elastic Properties M. Beghi, Milano Polytechnic, Italy A. G. Every, University of the Witwatersrand, South Africa P. Zinin, University of Hawaii, USA Theory and Applications of Acoustic Microscopy P. Zinin, University of Hawaii, USA Wieland Weise, Physikalisch-Technische Bundesanstalt, Braunschweig, Germany Ultrasonic Characterization of Biological Cells J. Bereiter-Hahn and C. Blase, J. W. Goethe University, Germany Ultrasonic Characterization of Hard Tissues Kay Raum, Martin Luther University of Halle-Wittenberg, Germany Clinical Applications of Ultrasonic NDE Y. Saijo, Tohoku University, Japan

Abstract: The experimental evidence and the associated theory are presented for the dislocation contribution to the generation of the second harmonic of an ultrasonic wave in solids. The contribution is measured through the changes, as a function of static bias stress, in the amplitude of the second harmonic of a fundamental wave (10 Mc/sec compressional wave) propagating in the specimen.In aluminum single crystals the amplitude of the second harmonic, for a given amplitude of the fundamental, changes markedly with static bias stresses ranging from 0 to 106 dyn/cm2. In alloys, there are essentially no changes of the amplitude of the second harmonic even for bias stresses up to 107 dyn/cm2. These observations are consistent with the predicted dependence of the amplitude on dislocation loop length and on the static stress. The effects of small amounts of plastic deformation were consistent with the proposed model.