Conventional ultrasonic methods based on ultrasonic characteristics in the linear elastic region are mainly sensitive to mature defects but are much less responsive to micro-damage or incipient material degradation. Recently, nonlinear ultrasonic characteristics beyond the linear ultrasonic amplitude range have been studied as a method for overcoming this limitation, and hence, many researchers are engaged in theoretical, experimental, and various application studies. However, the nonlinear ultrasonic characteristics are quite exacting compared to the linear phenomena so that they require vast experience and high proficiency in order to obtain proper experimental data. Actually, many researchers, especially beginners including graduate students, have difficulty in reliably measuring nonlinear ultrasonic characteristics. This book provides key technological know-how from experts with years of experience in this field, which will help researchers and engineers to obtain a clear understanding and high quality data in the nonlinear ultrasonic experiments and applications.

Conventional ultrasonic methods based on ultrasonic characteristics in the linear elastic region are mainly sensitive to mature defects but are much less responsive to micro-damage or incipient material degradation. Recently, nonlinear ultrasonic characteristics beyond the linear ultrasonic amplitude range have been studied as a method for overcoming this limitation, and hence, many researchers are engaged in theoretical, experimental, and various application studies. However, the nonlinear ultrasonic characteristics are quite exacting compared to the linear phenomena so that they require vast experience and high proficiency in order to obtain proper experimental data. Actually, many researchers, especially beginners including graduate students, have difficulty in reliably measuring nonlinear ultrasonic characteristics. This book provides key technological know-how from experts with years of experience in this field, which will help researchers and engineers to obtain a clear understanding and high quality data in the nonlinear ultrasonic experiments and applications.

The Rise of Smart Cities: Advanced Structural Sensing and Monitoring Systems provides engineers and researchers with a guide to the latest breakthroughs in the deployment of smart sensing and monitoring technologies. The book introduces readers to the latest innovations in the area of smart infrastructure-enabling technologies and howthey can be integrated into the planning and design of smart cities. With this book in hand, readers will find a valuable reference in terms of civil infrastructure health monitoring, advanced sensor network architectures, smart sensing materials, multifunctional material and structures, crowdsourced/social sensing, remote sensing and aerial sensing, and advanced computation in sensornetworks. Reviews the latest development in smart structural health monitoring (SHM) systems Introduces all major algorithms, with a focus on practical implementation Includes real-world applications and case studies Opens up a new horizon for robust structural sensing methods and their applications in smart cities

This multi-contributed volume provides a practical, applications-focused introduction to nonlinear acoustical techniques for nondestructive evaluation. Compared to linear techniques, nonlinear acoustical/ultrasonic techniques are much more sensitive to micro-cracks and other types of small distributed damages. Most materials and structures exhibit nonlinear behavior due to the formation of dislocation and micro-cracks from fatigue or other types of repetitive loadings well before detectable macro-cracks are formed. Nondestructive evaluation (NDE) tools that have been developed based on nonlinear acoustical techniques are capable of providing early warnings about the possibility of structural failure before detectable macro-cracks are formed. This book presents the full range of nonlinear acoustical techniques used today for NDE. The expert chapters cover both theoretical and experimental aspects, but always with an eye towards applications. Unlike other titles currently available, which treat nonlinearity as a physics problem and focus on different analytical derivations, the present volume emphasizes NDE applications over detailed analytical derivations. The introductory chapter presents the fundamentals in a manner accessible to anyone with an undergraduate degree in Engineering or Physics and equips the reader with all of the necessary background to understand the remaining chapters. This self-contained volume will be a valuable reference to graduate students through practising researchers in Engineering, Materials Science, and Physics. Represents the first book on nonlinear acoustical techniques for NDE applications Emphasizes applications of nonlinear acoustical techniques Presents the fundamental physics and mathematics behind nonlinear acoustical phenomenon in a simple, easily understood manner Covers a variety of popular NDE techniques based on nonlinear acoustics in a single volume

Ultrasonic Measurement Methods describes methods used in ultrasonic measurements and covers topics ranging from radiated fields of ultrasonic transducers to the measurement of ultrasonic velocity and ultrasonic attenuation, along with the physical principles of measurements with electromagnetic-acoustic transducers (EMATs). Optical detection of ultrasound and measurement of the electrical characteristics of piezoelectric devices are also examined. Comprised of seven chapters, this volume begins with an analysis of the radiated fields of ultrasonic transducers, followed by a discussion on the measurement of ultrasonic velocity and attenuation. The next chapter describes the physical principles of measurement with EMATs and the advantages of such devices based on their couplant-free operation. Optical detection of ultrasound is then considered, together with the problem of measuring the electrical characteristics of piezoelectric resonators and standard methods for obtaining the equivalent electrical parameter values. The final chapter is devoted to ultrasonic pulse scattering in solids and highlights many fascinating examples of wave scattering, some of which are accompanied by theoretical analysis. This book will be of interest to physicists.

The goal of this research is to find new noninvasive methods to certify the quality of safety-critical additively manufactured (AM) metallic parts for use in industries such as aerospace and defense. Additive manufacturing facilitates rapid prototyping, building, and repairing of custom components with increased agility, production rate, and reduced waste. A recognized barrier to the wide adoption of additive manufacturing is the lack of new approaches for AM part qualification. Our research objective is to exploit the material's linear and nonlinear ultrasonic response - which represents the measurable changes and distortion in elastic waves encountering macroscopic and microscopic defects - to establish links between microstructure and macroscale mechanical properties of AM metals. We measure linear and nonlinear ultrasonic parameters for a series of AM and wrought 316L grade stainless steel samples and compare the obtained parameters against mechanical properties of the samples measured on corresponding coupons. The samples are heat-treated to different temperatures to induce microstructural changes which alter their mechanical properties and ultrasonic response. Two sets of specimens are manufactured, one from the additive manufacturing method Laser Powder Bed Fusion (L-PBF), and the second from a traditional wrought method. Using the nonlinear ultrasonic method of Second Harmonic Generation (SHG), the acoustic nonlinearity parameter is estimated. SHG has been shown to offer a highly sensitive response to microstructural heterogeneities such as dislocations and grain boundaries. A linear ultrasonic parameter, wave speed, is also recorded with pulse-echo testing. Alongside these ultrasonic measurements, mechanical testing parameters including elastic moduli and yield strength are evaluated for the specimens. To accompany the experimental testing, a series of numerical simulations were conducted using commercial finite-element software to study the effects of randomly distributed heterogeneities on wave distortion in a controlled environment. In these simulations, randomly generated heterogeneities are scattered throughout a 2D plate with materials properties different from the bulk material. Ultrasonic wave propagation is simulated within this heterogeneous medium to investigate the effects of the heterogeneities' elastic properties, geometry, and distribution on ultrasonic signals, including distortion measured in terms of higher harmonic generation (HHG). Experimental results indicate correlations between the nonlinearity parameter and both ultimate tensile strength and yield strength, where nonlinearity generally decreases as these mechanical parameters increase, particularly in the AM samples. We hypothesize that microstructural changes in grain size and distribution through the heat treatment process influence these trends in measured nonlinearity. Additionally, substructures at even smaller length scales, such as nanoscale precipitates and dislocations affect the ultrasonic and mechanical behavior. Measurements of elastic moduli and total elongation do not exhibit trends with the nonlinearity parameter. The linear parameter, wave speed, does not correlate well with the mechanical parameters, which is attributed to its lack of sensitivity to detect changes in microscopic features. These results show promising evidence for the feasibility of AM parts qualification using nondestructive nonlinear ultrasonic testing. Results of the simulations indicate that changes in heterogeneity size, volume fraction, and material property deviations from the bulk material affect HHG to varying degrees. As expected, heterogeneities of smaller sizes and volume fractions have a less significant effect. However, at increasingly large values, changes in HHG are more pronounced, and material density and stiffness deviations from the bulk material are shown to have a larger effect on HHG. Future work includes continuing nonlinear ultrasonic testing, as well as comparing results to nonlinear resonant ultrasound spectroscopy (NRUS). New geometries and materials will be tested to expand the dataset. Microstructures will be imaged using scanning and transmission electron microscopy (SEM, TEM) and evaluate our hypotheses, and further complexity in numerical simulations will be implemented to isolate microstructural features and explore their effects on material behavior.