Acoustic and Elastic Waves: Recent Trends in Science and Engineering Dimitrios G. Aggelis and Nathalie Godin www.mdpi.com/journal/applsci Edited by Printed Edition of the Special Issue Published in Applied Sciences applied sciences Dimitrios G. Aggelis and Nathalie Godin (Eds.) Acoustic and Elastic Waves: Recent Trends in Science and Engineering This book is a reprint of the Special Issue that appeared in the online, open access journal, Applied Sciences (ISSN 2076-3417) from 2015–2016, available at: http://www.mdpi.com/journal/applsci/special_issues/acoustic_elastic_waves?view= default&listby=pubdate_published+DESC%2Cfirstpage+DESC%2Cnumber+DESC Guest Editors Dimitrios G. Aggelis Dept. Mechanics of Materials and Constructions (MeMC), Vrije Universiteit Brussel (VUB) Belgium Nathalie Godin Laboratoire MATEIS, National Institute for Applied Sciences (INSA) Lyon France Editorial Office Publisher Senior Assistant Editor MDPI AG Shu-Kun Lin Yurong Zhang St. Alban-Anlage 66 Basel, Switzerland 1. Edition 2016 ȱȊȱȱȊȱ Ȋȱ Ȋȱ Ȋ Belgrade ISBN 978-3-03842-296-9 (Hbk) ISBN 978-3-03842-297-6 (PDF) Articles in this volume are Open Access and distributed under the Creative Commons Attribution license (CC BY), which allows users to download, copy and build upon published articles even for commercial purposes, as long as the author and publisher are properly credited, which ensures maximum dissemination and a wider impact of our publications. The book taken as a whole is © 2016 MDPI, Basel, Switzerland, distributed under the terms and conditions of the Creative Commons by Attribution (CC BY-NC-ND) license (http://creativecommons.org/licenses/by-nc-nd/4.0/). III Table of Contents List of Contributors ......................................................................................................... VII About the Guest Editors ................................................................................................ XIV Preface to “Acoustic and Elastic Waves: Recent Trends in Science and Engineering” ............................................................................................................ XV Mathias Kersemans, Arvid Martens, Joris Degrieck, Koen Van Den Abeele, Steven Delrue, Lincy Pyl, Filip Zastavnik, Hugo Sol and Wim Van Paepegem The Ultrasonic Polar Scan for Composite Characterization and Damage Assessment: Past, Present and Future Reprinted from: Appl. Sci. 2016 , 6 (2), 58 http://www.mdpi.com/2076-3417/6/2/58.......................................................................... 1 Angélica Díaz, María T. Casas and Jordi Puiggalí Dispersion of Functionalized Silica Micro- and Nanoparticles into Poly(nonamethylene Azelate) by Ultrasonic Micro-Molding Reprinted from: Appl. Sci. 2015 , 5 (4), 1252–1271 http://www.mdpi.com/2076-3417/5/4/1252 .................................................................... 22 Adriana Savin, Alina Bruma, Rozina Steigmann, Nicoleta Iftimie and Dagmar Faktorova Enhancement of Spatial Resolution Using a Metamaterial Sensor in Nondestructive Evaluation Reprinted from: Appl. Sci. 2015 , 5 (4), 1412–1430 http://www.mdpi.com/2076-3417/5/4/1412 .................................................................... 45 Adriana Savin, Mihail-Liviu Craus, Vitalii Turchenko, Alina Bruma, Pierre-Antoine Dubos, Sylvie Malo, Tatiana E. Konstantinova and Valerii V. Burkhovetsky Monitoring Techniques of Cerium Stabilized Zirconia for Medical Prosthesis Reprinted from: Appl. Sci. 2015 , 5 (4), 1665–1682 http://www.mdpi.com/2076-3417/5/4/1665 .................................................................... 66 IV Giuseppe Lacidogna, Patrizia Cutugno, Gianni Niccolini, Stefano Invernizzi and Alberto Carpinteri Correlation between Earthquakes and AE Monitoring of Historical Buildings in Seismic Areas Reprinted from: Appl. Sci. 2015 , 5 (4), 1683–1698 http://www.mdpi.com/2076-3417/5/4/1683 .................................................................... 87 Maria Kogia, Liang Cheng, Abbas Mohimi, Vassilios Kappatos, Tat-Hean Gan, Wamadeva Balachandran and Cem Selcuk Electromagnetic Acoustic Transducers Applied to High Temperature Plates for Potential Use in the Solar Thermal Industry Reprinted from: Appl. Sci. 2015 , 5 (4), 1715–1734 http://www.mdpi.com/2076-3417/5/4/1715 .................................................................. 104 Eleni Tsangouri, Dimitrios G. Aggelis, Theodore E. Matikas and Anastasios C. Mpalaskas Acoustic Emission Activity for Characterizing Fracture of Marble under Bending Reprinted from: Appl. Sci. 2016 , 6 (1), 6 http://www.mdpi.com/2076-3417/6/1/6........................................................................ 128 Ryan Marks, Alastair Clarke, Carol Featherston, Christophe Paget and Rhys Pullin Lamb Wave Interaction with Adhesively Bonded Stiffeners and Disbonds Using 3D Vibrometry Reprinted from: Appl. Sci. 2016 , 6 (1), 12 http://www.mdpi.com/2076-3417/6/1/12...................................................................... 145 Michaël F. Hinderdael, Dieter De Baere and Patrick Guillaume Proof of Concept of Crack Localization Using Negative Pressure Waves in Closed Tubes for Later Application in Effective SHM System for Additive Manufactured Components Reprinted from: Appl. Sci. 2016 , 6 (2), 33 http://www.mdpi.com/2076-3417/6/2/33...................................................................... 173 V Nathalie Godin, Pascal Reynaud, Mohamed R’Mili and Gilbert Fantozzi Identification of a Critical Time with Acoustic Emission Monitoring during Static Fatigue Tests on Ceramic Matrix Composites: Towards Lifetime Prediction Reprinted from: Appl. Sci. 2016 , 6 (2), 43 http://www.mdpi.com/2076-3417/6/2/43...................................................................... 189 Tomaž Kek, Dragan Kusić and Janez Grum Wavelet Packet Decomposition to Characterize Injection Molding Tool Damage Reprinted from: Appl. Sci. 2016 , 6 (2), 45 http://www.mdpi.com/2076-3417/6/2/45...................................................................... 209 Wojciech Sas, Katarzyna Gabryś, Emil Soból and Alojzy Szymański Dynamic Characterization of Cohesive Material Based on Wave Velocity Measurements Reprinted from: Appl. Sci. 2016 , 6 (2), 49 http://www.mdpi.com/2076-3417/6/2/49...................................................................... 227 Shouzhao Sheng and Chenwu Sun Design of a Stability Augmentation System for an Unmanned Helicopter Based on Adaptive Control Techniques Reprinted from: Appl. Sci. 2015 , 5 (3), 575–586 http://www.mdpi.com/2076-3417/5/3/575.................................................................... 256 Klaudiusz Holeczek, Eric Starke, Anja Winkler, Martin Dannemann and Niels Modler Numerical and Experimental Characterization of Fiber-Reinforced Thermoplastic Composite Structures with Embedded Piezoelectric Sensor-Actuator Arrays for Ultrasonic Applications Reprinted from: Appl. Sci. 2016 , 6 (3), 55 http://www.mdpi.com/2076-3417/6/3/55...................................................................... 270 Linus De Roo, Lidewei L. Vergeynst, Niels J.F. De Baerdemaeker and Kathy Steppe Acoustic Emissions to Measure Drought-Induced Cavitation in Plants Reprinted from: Appl. Sci. 2016 , 6 (3), 71 http://www.mdpi.com/2076-3417/6/3/71...................................................................... 287 VI Xiaohui Zeng, Liang Zhang, Yang Yu, Min Shi and Jifu Zhou The Stiffness and Damping Characteristics of a Dual-Chamber Air Spring Device Applied to Motion Suppression of Marine Structures Reprinted from: Appl. Sci. 2016 , 6 (3), 74 http://www.mdpi.com/2076-3417/6/3/74...................................................................... 307 Francisco Sagasta, Amadeo Benavent-Climent, Andrés Roldán and Antolino Gallego Correlation of Plastic Strain Energy and Acoustic Emission Energy in Reinforced Concrete Structures Reprinted from: Appl. Sci. 2016 , 6 (3), 84 http://www.mdpi.com/2076-3417/6/3/84...................................................................... 333 Stefano Invernizzi , Giuseppe Lacidognaand Alberto Carpinteri Numerical Models for the Assessment of Historical Masonry Structures and Materials, Monitored by Acoustic Emission Reprinted from: Appl. Sci. 2016 , 6 (4), 102 http://www.mdpi.com/2076-3417/6/4/102.................................................................... 354 Piervincenzo Rizzo, Amir Nasrollahi, Wen Deng and Julie M. Vandenbossche Detecting the Presence of High Water-to-Cement Ratio in Concrete Surfaces Using Highly Nonlinear Solitary Waves Reprinted from: Appl. Sci. 2016 , 6 (4), 104 http://www.mdpi.com/2076-3417/6/4/104.................................................................... 372 Sanichiro Yoshida, David R. Didie, Daniel Didie, Tomohiro Sasaki, Hae-Sung Park, Ik-Keun Park and David Gurney Opto-Acoustic Method for the Characterization of Thin-Film Adhesion Reprinted from: Appl. Sci. 2016 , 6 (6), 163 http://www.mdpi.com/2076-3417/6/6/163.................................................................... 395 Antonella Saisi, Marco Guidobaldi and Carmelo Gentile On Site Investigation and Health Monitoring of a Historic Tower in Mantua, Italy Reprinted from: Appl. Sci. 2016 , 6 (6), 173 http://www.mdpi.com/2076-3417/6/6/173.................................................................... 421 VII List of Contributors Dimitrios G. Aggelis Department of Mechanics of Materials and Constructions, Vrije Universiteit Brussel, Pleinlaan 2, Brussels 1050, Belgium. Wamadeva Balachandran Brunel Innovation Centre (BIC), Brunel University, Cambridge CB21 2AL, UK. Amadeo Benavent-Climent Department of Mechanical Engineering, Polytechnic University of Madrid, Madrid 28006, Spain. Alina Bruma CRISMAT Laboratory, Ecole Nationale Superieure d’Ingenieurs de Caen, Universite de Caen Basse Normandie, 6 Blvd Marechal Juin, Caen 14050, France; Department of Physics and Astronomy, University of Texas at San Antonio, One University of Texas at San Antonio Circle, San Antonio, TX 78249, USA. Valerii V. Burkhovetsky Department of Physical Materials Science, Donetsk Institute for Physics and Engineering named after O.O. Galkin of National Academy of Sciences of Ukraine, 72 R. Luxemburg str., Donetsk 83114, Ukraine. Alberto Carpinteri Department of Structural, Geotechnical and Building Engineering, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy. María T. Casas Chemical Engineering Department, Polytechnic University of Catalonia, Av. Diagonal 647, Barcelona E-08028, Spain. Liang Cheng Brunel Innovation Centre (BIC), Brunel University, Cambridge CB21 2AL, UK. Alastair Clarke Cardiff School of Engineering, Cardiff University, Cardiff CF24 3AA, UK. Mihail-Liviu Craus Nondestructive Testing Department, National Institute for Research and Development for Technical Physics, 47 D. Mangeron Blvd., Iasi 700050, Romania; Frank Laboratory for Neutron Physics, Joint Institute for Nuclear Research, 6 Joliot-Curie Avenue, Dubna 141980, Russia. Patrizia Cutugno Department of Structural, Geotechnical and Building Engineering, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy. Martin Dannemann Institute of Lightweight Engineering and Polymer Technology (ILK), Technische Universität Dresden, Holbeinstraße 3, 01307 Dresden, Germany. VIII Niels J.F. De Baerdemaeker Laboratory of Plant Ecology, Department of Applied Ecology and Environmental Biology, Faculty of Bioscience Engineering, Ghent University, Coupure links 653, 9000 Gent, Belgium. Dieter De Baere Department of Mechanical Engineering, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium. Linus De Roo Laboratory of Plant Ecology, Department of Applied Ecology and Environmental Biology, Faculty of Bioscience Engineering, Ghent University, Coupure links 653, 9000 Gent, Belgium. Joris Degrieck Mechanics of Materials and Structures, Department of Materials Science and Engineering, Ghent University, Technologiepark-Zwijnaarde 903, 9052 Zwijnaarde, Belgium. Steven Delrue Wave Propagation and Signal Processing, Department of Physics, KULeuven-KULAK, Etienne-Sabbelaan 52, 8500 Kortrijk, Belgium. Wen Deng Laboratory for Nondestructive Evaluation and Structural Health Monitoring Studies, Department of Civil and Environmental Engineering, University of Pittsburgh, 3700 O’Hara Street, 729 Benedum Hall, Pittsburgh, PA 15261, USA; School of Automation, Northwestern Polytechnical University, Xi’an 710072, China. Angélica Díaz Chemical Engineering Department, Polytechnic University of Catalonia, Av. Diagonal 647, Barcelona E-08028, Spain. Daniel Didie Department of Chemistry and Physics, Southeastern Louisiana University, SLU 10878, Hammond, LA 70402, USA. David R. Didie Department of Chemistry and Physics, Southeastern Louisiana University, SLU 10878, Hammond, LA 70402, USA. Pierre-Antoine Dubos Laboratory of Crystallography and Materials Science (CRISMAT), CNRS-ENSICAEN-Université de Caen Basse Normandie, Caen 14050, France. Dagmar Faktorova Faculty of Electrical Engineering, University of Žilina, Univerzitná 1, Žilina 010 26, Slovakia. Gilbert Fantozzi INSA de Lyon, MATEIS (UMR CNRS 5510), 7 avenue Jean Capelle, 69621 Villeurbanne Cedex, France. Carol Featherston Cardiff School of Engineering, Cardiff University, Cardiff CF24 3AA, UK. Katarzyna Gabryś Water Centre Laboratory, Faculty of Civil and Environmental Engineering, Warsaw University of Life Sciences, 02-787 Warsaw, Poland. IX Antolino Gallego Department of Applied Physics, University of Granada, Granada 18071, Spain. Tat-Hean Gan TWI Ltd., Granta Park, Great Abington, Cambridge CB21 6AL, UK; Brunel Innovation Centre (BIC), Brunel University, Cambridge CB21 2AL, UK. Carmelo Gentile Department Architecture, Built environment and Construction engineering (DABC), Politecnico di Milano, P.za Leonardo da Vinci 32, Milan 20133, Italy. Nathalie Godin INSA de Lyon, MATEIS (UMR CNRS 5510), 7 avenue Jean Capelle, 69621 Villeurbanne Cedex, France. Janez Grum Faculty of Mechanical Engineering, University of Ljubljana, Aškerčeva 6, Ljubljana 1000, Slovenia. Marco Guidobaldi Department Architecture, Built environment and Construction engineering (DABC), Politecnico di Milano, P.za Leonardo da Vinci 32, Milan 20133, Italy. Patrick Guillaume Department of Mechanical Engineering, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium. David Gurney Department of Chemistry and Physics, Southeastern Louisiana University, SLU 10878, Hammond, LA 70402, USA. Michaël F. Hinderdael Department of Mechanical Engineering, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium. Klaudiusz Holeczek Institute of Lightweight Engineering and Polymer Technology (ILK), Technische Universität Dresden, Holbeinstraße 3, 01307 Dresden, Germany. Nicoleta Iftimie Nondestructive Testing Department, National Institute of R&D for Technical Physics, Iasi 700050, Romania. Stefano Invernizzi Department of Structural, Geotechnical and Building Engineering, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy. Vassilios Kappatos Brunel Innovation Centre (BIC), Brunel University, Cambridge CB21 2AL, UK. Tomaž Kek Faculty of Mechanical Engineering, University of Ljubljana, Aškerčeva 6, Ljubljana 1000, Slovenia. Mathias Kersemans Mechanics of Materials and Structures, Department of Materials Science and Engineering, Ghent University, Technologiepark- Zwijnaarde 903, 9052 Zwijnaarde, Belgium. X Maria Kogia Brunel Innovation Centre (BIC), Brunel University, Cambridge CB21 2AL, UK. Tatiana E. Konstantinova Department of Physical Materials Science, Donetsk Institute for Physics and Engineering named after O.O. Galkin of National Academy of Sciences of Ukraine, 72 R. Luxemburg str., Donetsk 83114, Ukraine. Dragan Kusić TECOS Slovenian Tool and Die Development Centre, Kidričeva 25, Celje 3000, Slovenia. Giuseppe Lacidogna Department of Structural, Geotechnical and Building Engineering, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy. Sylvie Malo Laboratory of Crystallography and Materials Science (CRISMAT), CNRS-ENSICAEN-Université de Caen Basse Normandie, Caen 14050, France. Ryan Marks Cardiff School of Engineering, Cardiff University, Cardiff CF24 3AA, UK. Arvid Martens Wave Propagation and Signal Processing, Department of Physics, KULeuven-KULAK, Etienne-Sabbelaan 52, 8500 Kortrijk, Belgium. Theodore E. Matikas Department Materials Science and Engineering, University of Ioannina, Ioannina 45110, Greece. Niels Modler Institute of Lightweight Engineering and Polymer Technology (ILK), Technische Universität Dresden, Holbeinstraße 3, 01307 Dresden, Germany. Abbas Mohimi TWI Ltd., Granta Park, Great Abington, Cambridge CB21 6AL, UK;Brunel Innovation Centre (BIC), Brunel University, Cambridge CB21 2AL, UK. Anastasios C. Mpalaskas Department Materials Science and Engineering, University of Ioannina, Ioannina 45110, Greece. Amir Nasrollahi Laboratory for Nondestructive Evaluation and Structural Health Monitoring Studies, Department of Civil and Environmental Engineering, University of Pittsburgh, 3700 O’Hara Street, 729 Benedum Hall, Pittsburgh, PA 15261, USA. Gianni Niccolini Department of Structural, Geotechnical and Building Engineering, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy. Christophe Paget Airbus UK Ltd., Filton, Bristol BS99 7AR, UK. Hae-Sung Park Department of Mechanical Engineering, The Graduate School, Seoul National University of Science and Technology, 232 Gongneung-ro, Nowon-gu, Seoul 01811, Korea. XI Ik-Keun Park Department of Mechanical and Automotive Engineering, Seoul National University of Science and Technology, 232 Gongneung-ro, Nowon-gu, Seoul 01811, Korea. Jordi Puiggalí Chemical Engineering Department, Polytechnic University of Catalonia, Av. Diagonal 647, Barcelona E-08028, Spain. Rhys Pullin Cardiff School of Engineering, Cardiff University, Cardiff CF24 3AA, UK. Lincy Pyl Department Mechanics of Materials and Constructions, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium. Mohamed R’Mili INSA de Lyon, MATEIS (UMR CNRS 5510), 7 avenue Jean Capelle, 69621 Villeurbanne Cedex, France. Pascal Reynaud INSA de Lyon, MATEIS (UMR CNRS 5510), 7 avenue Jean Capelle, 69621 Villeurbanne Cedex, France. Piervincenzo Rizzo Laboratory for Nondestructive Evaluation and Structural Health Monitoring Studies, Department of Civil and Environmental Engineering, University of Pittsburgh, 3700 O’Hara Street, 729 Benedum Hall, Pittsburgh, PA 15261, USA. Andrés Roldán Department of Electronics and Computer Technology, University of Granada, Granada 18071, Spain. Francisco Sagasta Department of Applied Physics, University of Granada, Granada 18071, Spain. Antonella Saisi Department Architecture, Built environment and Construction engineering (DABC), Politecnico di Milano, P.za Leonardo da Vinci 32, Milan 20133, Italy. Wojciech Sas Water Centre Laboratory, Faculty of Civil and Environmental Engineering, Warsaw University of Life Sciences, 02-787 Warsaw, Poland. Tomohiro Sasaki Department of Mechanical Engineering, Niigata University, Ikarashi Ninocho 8050, Nishi-ku, Niigata-shi, Niigata 950-2181, Japan. Adriana Savin Nondestructive Testing Department, National Institute of R&D for Technical Physics, Iasi 700050, Romania; Nondestructive Testing Department, National Institute for Research and Development for Technical Physics, 47 D. Mangeron Blvd., Iasi 700050, Romania. Cem Selcuk Brunel Innovation Centre (BIC), Brunel University, Cambridge CB21 2AL, UK. XII Shouzhao Sheng College of Automation Engineering, Nanjing University of Aeronautics and Astronautics, 29 YuDao St., Nanjing 210016, China. Min Shi Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China. Emil Soból Department of Geotechnical Engineering, Faculty of Civil and Environmental Engineering, Warsaw University of Life Sciences, 02-787 Warsaw, Poland. Hugo Sol Department Mechanics of Materials and Constructions, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium. Eric Starke Institute of Lightweight Engineering and Polymer Technology (ILK), Technische Universität Dresden, Holbeinstraße 3, 01307 Dresden, Germany. Rozina Steigmann Nondestructive Testing Department, National Institute of R&D for Technical Physics, Iasi 700050, Romania; Faculty of Physics, University Al.I. Cuza, 11 Carol I Blvd, Iasi 700506, Romania. Kathy Steppe Laboratory of Plant Ecology, Department of Applied Ecology and Environmental Biology, Faculty of Bioscience Engineering, Ghent University, Coupure links 653, 9000 Gent, Belgium. Chenwu Sun College of Automation Engineering, Nanjing University of Aeronautics and Astronautics, 29 YuDao St., Nanjing 210016, China. Alojzy Szymański Department of Geotechnical Engineering, Faculty of Civil and Environmental Engineering, Warsaw University of Life Sciences, 02-787 Warsaw, Poland. Eleni Tsangouri Department of Mechanics of Materials and Constructions, Vrije Universiteit Brussel, Pleinlaan 2, Brussels 1050, Belgium. Vitalii Turchenko Frank Laboratory for Neutron Physics, Joint Institute for Nuclear Research, 6 Joliot-Curie Avenue, Dubna 141980, Russia. Koen Van Den Abeele Wave Propagation and Signal Processing, Department of Physics, KULeuven-KULAK, Etienne-Sabbelaan 52, 8500 Kortrijk, Belgium. Wim Van Paepegem Mechanics of Materials and Structures, Department of Materials Science and Engineering, Ghent University, Technologiepark- Zwijnaarde 903, 9052 Zwijnaarde, Belgium. Julie M. Vandenbossche Department of Civil and Environmental Engineering, University of Pittsburgh, 3700 O’Hara Street, 705 Benedum Hall, Pittsburgh, PA 15261, USA. XIII Lidewei L. Vergeynst Laboratory of Plant Ecology, Department of Applied Ecology and Environmental Biology, Faculty of Bioscience Engineering, Ghent University, Coupure links 653, 9000 Gent, Belgium. Anja Winkler Institute of Lightweight Engineering and Polymer Technology (ILK), Technische Universität Dresden, Holbeinstraße 3, 01307 Dresden, Germany. Sanichiro Yoshida Department of Chemistry and Physics, Southeastern Louisiana University, SLU 10878, Hammond, LA 70402, USA. Yang Yu Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration, State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, Tianjin 300072, China. Filip Zastavnik Department Mechanics of Materials and Constructions, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium. Xiaohui Zeng Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China. Liang Zhang Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China. Jifu Zhou Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China. XIV About the Guest Editors Dimitrios Aggelis is a Professor of the Department of Mechanics of Materials and Constructions at the Vrije (Free) University of Brussels, Belgium since October 2012. Prior to this position, he worked as an Assistant Professor in the Department of Materials Science and Engineering at the University of Ioannina, Greece (2008–2012) and as a research fellow in the Research Institute of Technology, Tobishima Corporation, Japan (2006–2008). He received his PhD degree from the Mechanical Engineering and Aeronautics Department of the University of Patras in 2004. His main area of interest includes characterization of cementitious materials, expanding also to composites and metals by use of non-destructive inspection techniques focused on elastic wave propagation. He is an active member of several technical committees of RILEM, the secretary of IAM (Damage Assessment in Consideration of Repair/Retrofit-Recovery in Concrete and Masonry Structures by Means of Innovative NDT) and was the recipient of the RILEM Robert L’Hermite medal in 2012 for outstanding contribution in the field of construction materials monitoring. He has published more than 110 papers in international journals and more than 120 papers in conference proceedings along with 10 chapters in books or stand-alone books. He is editor of the journal Construction and Building Materials and editorial board member of other international journals (incl., Applied Sciences and NDT&E International ). He is currently, or has been involved in, teaching of Dynamics of Structures, Experimental Techniques and Non-destructive Testing of Materials, Mechanics of Materials, and Construction Materials. He was the chairman of the International Conference of Emerging Technologies in Non-Destructive Testing 6 (ETNDT6) held in Brussels, 27–29 May 2015, while he is the co-chairing the 2nd International RILEM Conference on Early Age Cracking and Serviceability in Cement-Based Materials and Structures (EAC2), 12–14 September, 2017, in Brussels, Belgium. Nathalie Godin , Ph.D., is an Associate Professor at the National Institute of Applied Sciences (INSA) in Lyon, France since 1996. She received her PhD degree from the University of Bordeaux in 1994. She has 20 years of experience in AE and in the analysis of damage to various classes of materials. She focuses on fiber- reinforced composites as these materials have a variety of applications and they are quickly being adopted in a number of industries. She has authored over 40 articles and two book chapters and has been an invited speaker at numerous professional research conferences. She is also a board member of the French Society for Composite Materials (AMAC). XV Preface to “Acoustic and Elastic Waves: Recent Trends in Science and Engineering” Elastic waves in the active (ultrasound) and passive form (acoustic emission) provide an ideal approach for the non-destructive inspection of materials. They are used for all types of materials and structures, having many advantages over other traditional measurements. Although they are already applied in a usual basis in the structural health monitoring of structures, new challenges arise. These are related to pushing the limit of the characterization capacity further: detecting smaller cracks, providing more information on the condition of the material, predicting the useful life time, and characterizing new innovative materials that have not been tested before. The articles contained in this issue/book include a broad range of materials from masonry and concrete to ceramics, composites, 3D printed metals and medical prosthetics and structures from cultural heritage towers and concrete beams to marine and aeronautic structures and solar panels. Characterization concerns the fracture mode, remaining fatigue life, disbonds in bonded stiffeners, localization of defects, condition of injection molding tools and many others. We believe that this book constitutes an up-to-date collection of cutting edge applications of acoustic/elastic wave techniques, many of which were presented in the International Conference on Emerging Technologies in Non-Destructive Testing (ETNDT6) in Brussels, 27–29 May 2015. We wish to thank all the authors for submitting their work and the reviewers who contributed to the high final quality of the presented studies. Dimitrios G. Aggelis and Nathalie Godin Guest Editors The Ultrasonic Polar Scan for Composite Characterization and Damage Assessment: Past, Present and Future Mathias Kersemans, Arvid Martens, Joris Degrieck, Koen Van Den Abeele, Steven Delrue, Lincy Pyl, Filip Zastavnik, Hugo Sol and Wim Van Paepegem Abstract: In the early 1980’s, the ultrasonic polar scan (UPS) technique was developed to assess the fiber direction of composites in a nondestructive way. In spite of the recognition by several researchers as being a sophisticated and promising methodology for nondestructive testing (NDT) and materials science, little advance was made during the following 30 years. Recently however, the UPS technique experienced a strong revival and various modifications to the original UPS setup have been successfully implemented. This revival has exposed several powerful capabilities and interesting applications of the UPS technique for material characterization and damage assessment. This paper gives a short historical overview of the UPS technique for characterizing and inspecting (damaged) fiber-reinforced plastics. In addition, a few future research lines are given, which will further expand the applicability and potential of the UPS method to a broader range of (damaged) materials, bringing the UPS technique to the next level of maturity. Reprinted from Appl. Sci. Cite as: Kersemans, M.; Martens, A.; Degrieck, J.; Van Den Abeele, K.; Delrue, S.; Pyl, L.; Zastavnik, F.; Sol, H.; Van Paepegem, W. The Ultrasonic Polar Scan for Composite Characterization and Damage Assessment: Past, Present and Future. Appl. Sci. 2016 , 6 , 58. 1. Introduction An ultrasonic polar scan (UPS) is obtained by replacing the translational movement of a classical ultrasonic C-scan setup with a rotational movement. Hence, instead of scanning a plate surface at normal incidence, the UPS insonifies a certain material spot from as many oblique incidence angles ψ p φ , θ q as possible [1]. A schematic of the UPS method is presented in Figure 1a. Depending on the employed ultrasound, we speak of a pulsed ultrasonic polar scan (P-UPS) for a broadband pulse or a harmonic ultrasonic polar scan (H-UPS) for mono-frequency ultrasound. To improve coupling of the ultrasonic wave energy in the sample, the plate sample is immersed in water. Simply recording the transmitted (or reflected) ultrasound amplitude then yields a UPS image. Figure 1b,c shows current state-of-the-art P-UPS recordings for aluminum and [0 ̋ ] 8 carbon/epoxy (C/E) 1 laminate, using an ultrasonic pulse with central frequency f c = 5 MHz. The vertical incident angle θ is placed on the radial axis, the in-plane polar angle φ is represented along the angular axis, while the assigned gray (or color) scale is a measure of the transmitted (or reflected) pulse amplitude. Hence, the P-UPS image comprises a large collection of amplitudes of obliquely transmitted (or reflected) ultrasound pulses. Figure 1. Schematic of ultrasonic polar scan (UPS) method ( a ). State-of-the-art pulsed ultrasonic polar scan (P-UPS) recordings at f c = 5 MHz: aluminum with thickness d = 0.6 mm ( b ) and [0 ̋ ] 8 C/E laminate with thickness d = 1.1 mm ( c ). “QL”, “QT-H” and “QT-V” stand for quasi-longitudinal wave and quasi-transverse wave with horizontal and vertical polarization respectively. Within the amplitude landscape of the P-UPS, characteristic contours emerge that more or less relate to the condition for critical (or in-plane) stimulation of the quasi-longitudinal, horizontally and vertically polarized quasi-transverse wave modes [ 2 ]. Note that along symmetry orientations, the prefix “quasi-” may be omitted, resulting in pure wave modes. These stimulation conditions are of course linked to the mechanical properties, like elasticity, of the insonified plate sample through Christoffel’s equation and Snell’s law [ 3 , 4 ]. As such, the P-UPS image actually represents an acoustic fingerprint of the mechanical properties. In the example of Figure 1b, the circular symmetry clearly puts on view the isotropic mechanical nature of the aluminum sample. The isotropic nature further invokes a degeneration of the quasi-transverse horizontal and quasi-transverse vertical wave, thus resulting in a P-UPS image with two characteristic contours. Figure 1c, on the other hand, displays a stretched appearance due to the unidirectional nature of the [0 ̋ ] 8 C/E laminate. Higher stiffness values lead to smaller critical angles (Snell’s law), and thus correspond to the contours being locally pressed inward in the P-UPS image. Considering the inner contour of Figure 1c, which is dominated by the quasi-longitudinally polarized wave, one can immediately determine that highest stiffness is found along φ = 0 ̋ , which obviously corresponds to the orientation of the carbon reinforcement fibers of the [0 ̋ ] 8 C/E laminate. 2 In the remainder of this manuscript, a historical overview of the UPS research is given, starting from the initial results of the pioneering researchers, going over our recent advances [5], and finishing with currently investigated research lines. 2. The Past: 1981–2010 In the early 1980’s, the UPS technique was first introduced by Van Dreumel and Speijer in a pulsed version in order to assess the fiber orientation of composites [ 1 ]. The beauty of the intriguing patterns made the pioneering authors state [ 1 ]: “ A library of Polar-patterns, stored as ‘fingerprints’, raises the possibility of laminate identification by pattern recognition ”. It is unfortunate that in the following years, only one sequel study was performed by Van Dreumel and Speyer to further explore the capabilities of the ultrasonic polar scan [6]. It took fifteen years before the technique was investigated again through the work of Degrieck [7–9]. He used a modernized scanning system to obtain more accurate and detailed P-UPS experiments. The work of Degrieck has identified several practical applications of the P-UPS technique for composite materials: (i) estimation of fiber direction; (ii) determination of fiber volume fraction and porosity and (iii) detection of fatigue damage [ 8 , 9 ]. In addition, he and Van Leeuwen implemented a numerical procedure for simulating P-UPS images of homogeneous composites [ 7 ], in view of bringing the technique to the next level: full quantitative characterization of the elastic properties of composite materials using a mixed experimental-numerical approach. Although the gap between experiment and simulation was not yet bridged, their numerical results did contribute to the physical understanding of the formation of a P-UPS image. They found that the characteristic patterns are (more or less) a representation of critical bulk wave angles, while the global transmission amplitude exposes attenuation properties [ 8 ]. Consequently, a P-UPS image may be used for characterizing viscoelastic material properties. The ultrasonic polar scan research has been further extended by Declercq, first as a student of Degrieck [ 2 , 10 , 11 ] and afterwards as a professor at the Georgia Institute of Technology in Metz [ 12 ]. He applied the technique for detecting tension-tension induced fatigue damage in glass fiber composites by tracing shifts in the characteristic fingerprint [ 10 ]. In addition, Declercq extended the simulation technique towards layered viscoelastic materials having arbitrary anisotropy using a global matrix method [ 2 , 11 ]. He experimentally implemented a time-of-flight (TOF) version of the P-UPS method and commented on the superior sensitivity (compared with amplitude recording) to the presence of damage features [ 12 ]. Here, TOF is defined as the arrival time of the peak amplitude of the transmitted ultrasound pulse. As an illustration, Figure 2 displays state-of-the-art amplitude and TOF landscape of a P-UPS for a [0 ̋ ] 8 C/E laminate [13]. 3