The theme of the 15th International Acoustic Emission Symposium (IAES15) was set as 'practicality for life-extension and maintenance of plants and structures'. Special emphasis was placed on the review of acoustic emission (AE) research and applications in the 20th century and its future in the 21st century. The technique for monitoring defects and abnormal vibrations due to machine failures is vitally important for the safety of structures in a modern society. AE, as a passive, rather than an active NDT method, has drawn much attention because of its applicability to on-stream surveillance of structures. One important point is its capability to acquire data very simply but with high sensitivity so that the development of a non-contact sensing technique is particularly important. A quantitative method to evaluate structural integrity and remaining life from the detected AE signals is strongly required. Quantitative analysis, based on inverse procedures, has provided a certain solution, but has not been utilized widely enough in structures due to its complexity. Its applicability is limited partly because the accuracy of solutions depends on noise levels and partly because the phenomenon is usually non-reproducible. AE is expected to be a next-generation technique not only to monitor conditions but also for the repair of damaged structures, combined with an active-adaptive technique using a 'solid state actuator'. 'Smart Materials and Structures' are known in this respect. AE is considered to be a very promising technique, together with such sensing techniques as optical fiber, shape memory alloy and electro-rheological fluid. Thus, AE can play a very important roll in monitoring, evaluating and repairing structures. In this workshop, a limited number of invited papers are presented for technical discussion to review the achievements of AE research and applications in the 20th century. The proceedings are entitled Acoustic Emission - Beyond the Millennium to celebrate the new millennium, and stepping forward to a new era. The authors and topics of these review papers were selected by the editorial board.

EWGAE 2006 Proceedings of the 27th European Conference on Acoustic Emission Testing (EWGAE 2006), Cardiff, Wales, UK, September 20th – 22nd 2006

The Acoustic Emission (AE) technique uses ad hoc transducers to detect AE events caused by crack growth in structures under external loading. This technique is similar to the one employed in earthquake control, where seismic waves reach the monitoring stations placed on the surface of the Earth. And although they take place on different scales, the

This book provides an introduction to Acoustic Emission Testing and its applications to different materials like concrete, steel, ceramics, geotechnical materials, polymers, biological structures and wood. Acoustic Emission Techniques (AET) techniques have been studied in engineering for a long time. The techniques are applied more and more to practical investigations and are more and more standardized in codes. This is because the degradation of structures due to ageing urgently demand for maintenance and rehabilitation of structures in service. It results in the need for the development of advanced and efficient inspection techniques. In mechanical engineering and concerning the monitoring of machines and mechanical components, AE is a widely accepted observing deterioration in the frame of structural health monitoring. The advantages of AE like sensitivity, damage localization potential, non-intrusive nature as well as developments in signal analysis and data transmission allow applications that could not be considered decades ago. As such, AE techniques draw great attention to diagnostic applications and in material testing. This book covers all levels from the description of AE basics for AE beginners (level of a student) to sophisticated AE algorithms and applications to real large-scale structures as well as the observation of the cracking process in laboratory specimen to study fracture processes. This book has proved its worth over the past twelve years. Now in its second edition, it will be a resource that sets the standard and equips readers for the future. All chapters from the 1st edition have been updated and rewritten and eight extra chapters (e.g also regarding AE tomography, AE in plate-like structures and AE for investigations of hardening of fresh concrete) have been added.

This thesis provides an innovative strategy for rail crack monitoring using the acoustic emission (AE) technique. The field study presented is a significant improvement on laboratory studies in the literature in terms of complex rail profile and crack conditions as well as high operational noise. AE waves induced by crack propagation, crack closure, wheel-rail impact and operational noise were obtained through a series of laboratory and field tests, and analyzed by wavelet transform (WT) and synchrosqueezed wavelet transform (SWT). A wavelet power-based index and the enhanced SWT scalogram were sequentially proposed to classify AE waves induced by different mechanisms according to their energy distributions in the time–frequency domain. A novel crack sizing method taking advantage of crack closure-induced AE waves was developed based on fatigue tests in the laboratory. The propagation characteristics of AE waves in the rail were investigated, and Tsallis synchrosqueezed wavelet entropy (TSWE) with time was finally brought forward to detect and locate rail cracks in the field. The proposed strategy for detection, location and sizing of rail cracks helps to ensure the safe and smooth operation of the railway system. This thesis is of interest to graduate students, researchers and practitioners in the area of structural health monitoring.

Acoustic emission (AE) techniques have successfully been used for assuring the structural integrity of large rocket motorcases since 1963, and their uses have expanded to ever larger structures, especially as structural health monitoring (SHM) of large structures has become the most urgent task for engineering communities around the world. The needs for advanced AE monitoring methods are felt keenly by those dealing with aging infrastructures. Many publications have appeared covering various aspects of AE techniques, but documentation of actual applications of AE techniques has been mostly limited to reports of successful results without technical details that allow objective evaluation of the results. There are some exceptions in the literature. In this Special Issue of the Acoustics section of Applied Sciences, we seek contributions covering these exceptions cited here. Here, we seek contributions describing case histories of AE applications to large structures that have achieved the goals of SHM by providing adequate technical information supporting the success stories. Types of structures can include aerospace and geological structures, bridges, buildings, factories, maritime facilities, off-shore structures, etc. Experiences with AE monitoring methods designed and proven for large stru