Preface

Acoustic emission (AE) is a phenomenon involving sound wave generation by materials subject to deformation, fracture, and chemical reactions. The use of AE has been growing tremendously in process monitoring and quality control in manufacturing processes since its discovery in the early 1950s in Germany. Structural testing and assessment, process monitoring, and material characterization constitute three broad application areas of AE techniques. Quantitative and qualitative characteristics of AE waves have been studied widely in the literature. This book reviews major research developments over the past few years in application of AE in numerous fields, including aerospace, automotive, biomedical, manufacturing, and civil and materials engineering fields. It brings together important contributions from renowned international researchers to provide an excellent survey of new perspectives and paradigms of acoustic emissions. In particular, this book presents applications of AE in cracking and damage assessment in metal beams, asphalt pavements, and composite materials as well as studying noise mitigation in wind turbines and cylindrical shells.

Chapter 1 introduces the AE technique by providing a brief background and summarizing the application areas of AE including aerospace, automotive, biomedical, manufacturing, and civil and materials engineering fields. Chapter 2 is devoted to cracking and damage assessment in Steel-Reinforced Concrete (Steel-RC) beams and Glass Fiber-Reinforced Polymer–Reinforced Concrete (GFRP-RC) beams. The AE technique is shown to be an effective Non-Destructive Testing (NDT) tool for concrete structures. The behavior of cracks of the RC beams from loading to failure using an AE parameter analysis-based method is analyzed. The chapter provides a classification of the crack types and damage levels that occur in these RC beams with varying percentage tension reinforcement ratios. Chapter 3 focuses on various applications of the AE technique in evaluating low-temperature cracking in asphalt pavement materials including: (1) assessment of low-temperature cracking performance of asphalt binders and asphalt mixtures and (2) quantitative characterization of rejuvenators' efficiency in restoring aged asphalt pavements to their crack-resistant state. The AE-based embrittlement temperature results of twenty-four different asphalt materials consisting of eight different binders, each at three oxidative aging levels, are presented. Results show that the AE-based embrittlement temperatures were consistently lower than the Bending Beam Rheometer (BBR-based) critical cracking temperatures. Chapter 4 deals with polymer matrix-based composites that are widely used for various applications in aerospace, automobile, marine, sports, construction, and electrical industries. Complicated defects like delamination present in the composite laminates can be detected effectively using nonlinear acoustic wave spectroscopy (NAWS). One NAWS technique for detecting delamination is based on intensification of vibration amplitudes at the delamination location, known as the local defect resonance (LDR) technique. This technique is quite established in early detection of damages in composite structures. In this chapter, a numerical investigation for detecting delamination in GFRP composite based on the vibro- thermography technique is discussed. A single periodic LDR frequency excitation is used to excite the GFRP plate, resulting in a local temperature rise at delamination region due to frictional

heating at the damage interface. An explicit dynamic temperature displacement analysis is carried out for a specific period of LDR excitation. Subsequently, a heat transfer analysis is performed to observe the temperature difference at the top surface of the delaminated GFRP plate. A numerical investigation is carried out based on LDR excitation for high-contrast imaging of delamination in composite materials using vibro-thermography. Chapter 5 presents an analysis of sound radiation from periodic Acoustic Black Hole (ABH) shells. It is shown that by reducing thickness according to the power law, the wave velocity is substantially lowered, while the wave number is increased when it propagates to the ABH center, where the damping dissipates the vibrational energy very efficiently. The focus is placed on reducing the sound emission from cylindrical shells via embedding periodic ABHs. Finally, Chapter 6 presents a computational analysis of trailing edge bluntness vortex shedding noise for a 2-MW horizontal axis wind turbine (HAWT) for trailing edge thicknesses of 0.1 % and 0.5 % local chord using the original Brooks–Pope–Marcolini (BPM) model. The original BPM and the modified BPM results for trailing edge bluntness noise are clearly presented.

> **Mahmut Reyhanoglu** Columbus State University, United States of America
