Sound Waves and Acoustic Emission PDF
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Synthesis Lectures on Wave Phenomena in the Physical Sciences Claudia Barile · Caterina Casavola · Giovanni Pappalettera · Vimalathithan Paramsamy Kannan Sound Waves and Acoustic Emission Synthesis Lectures on Wave Phenomena in the Physical Sciences Series Editor Sanichiro Yoshida, Department of Chemistry and Physics, Southeastern Louisiana University, Hammond, LA, USA The aim of this series is to discuss the science of various waves. An emphasis is laid on graspingthebigpictureofeachsubjectwithoutdealingformalism,andyetunderstanding thepracticalaspectsofthesubject.Tothisend,mathematicalformulationsaresimplified as much as possible and applications to cutting edge research are included. Claudia Barile Caterina Casavola (cid:1) (cid:129) Giovanni Pappalettera (cid:1) Vimalathithan Paramsamy Kannan Sound Waves and Acoustic Emission 123 ClaudiaBarile Caterina Casavola Department ofMechanics Department ofMechanics Mathematics, andManagement Mathematics, andManagement Polytechnic University ofBari Polytechnic University ofBari Bari, Italy Bari, Italy GiovanniPappalettera Vimalathithan Paramsamy Kannan Department ofMechanics Department ofMechanics Mathematics, andManagement Mathematics, andManagement Polytechnic University ofBari Polytechnic University ofBari Bari, Italy Bari, Italy ISSN 2690-2346 ISSN 2690-2354 (electronic) Synthesis Lectures onWave Phenomena inthe Physical Sciences ISBN978-3-031-23788-1 ISBN978-3-031-23789-8 (eBook) https://doi.org/10.1007/978-3-031-23789-8 ©TheEditor(s)(ifapplicable)andTheAuthor(s),underexclusivelicensetoSpringerNature SwitzerlandAG2023 Thisworkissubjecttocopyright.AllrightsaresolelyandexclusivelylicensedbythePublisher,whetherthe wholeorpartofthematerialisconcerned,specificallytherightsoftranslation,reprinting,reuseofillustrations, recitation,broadcasting,reproductiononmicrofilmsorinanyotherphysicalway,andtransmissionorinformation storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now knownorhereafterdeveloped. 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ThisSpringerimprintispublishedbytheregisteredcompanySpringerNatureSwitzerlandAG Theregisteredcompanyaddressis:Gewerbestrasse11,6330Cham,Switzerland Contents 1 What is Sound? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.1 Perception of Sound. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 How Does Sound Travel? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.3 Properties of Sound . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.4 Speed of Sound. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2 Propagation of Sound Waves. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.1 Simple Harmonic Vibrations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.2 Damped Vibrations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 2.3 Propagation of Waves on a String. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 2.4 Solution for the Wave Equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 2.4.1 Wave Energy of the Transverse Wave . . . . . . . . . . . . . . . . . . . . 21 2.4.2 Reflection of the Transverse Wave at a Boundary. . . . . . . . . . . . 24 2.5 Longitudinal Wave Propagation in Bars . . . . . . . . . . . . . . . . . . . . . . . . 25 2.5.1 Longitudinal Wave Equation . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 2.6 Transverse Wave Propagation in Bars. . . . . . . . . . . . . . . . . . . . . . . . . . 28 2.7 Dispersion of Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 3 Acoustic Emission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 3.1 Propagation of Elastic Waves. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 3.1.1 Longitudinal Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 3.1.2 Transverse Waves. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 3.1.3 Rayleigh Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 3.1.4 Lamb Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 3.1.5 Other Waves. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 3.2 Attenuation and Distortion of Elastic Waves . . . . . . . . . . . . . . . . . . . . . 40 4 Acousto-Ultrasonics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 4.1 Brief Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 4.2 Stress Wave Factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 4.3 Attenuation and Dispersion of Acousto-Ultrasonic Stress Waves . . . . . . 46 References. .... .... .... .... .... ..... .... .... .... .... .... ..... .... 51 v About the Authors ClaudiaBarile isanAssociateProfessorofMechanicalDesignandExperimentalDesign at Politecnico di Bari where she is also a lecturer at the Bachelor and Master Degree of IndustrialDesignandattheMasterDegreeofMechanicalEngineering.Hermainresearch interests are connected with material characterization and experimental mechanics including strain gauges methods, acoustic emission, and residual stress analysis. She is a member of the Ph.D. committee in Mechanical and Management Engineering at Politecnico di Bari. She is the author of more than one hundred papers published in international journals andconference proceedings. Sheistheco-author offive booksand member of international and national associations including the Society of Experimental Mechanics,theEuropeanSocietyofExperimentalMechanics,andtheSocietàScientifica Italiana di Progettazione Meccanica e Costruzione di Macchine. Prof.CaterinaCasavola isaFullProfessorofMechanicalDesignatPolitecnicodiBari, and she teaches the Design of Innovative Materials, Experimentation on Aerostructures, and Experimental Mechanics. Her research activity is concerned with mechanical characterization of innovative materials, experimental stress analysis on real components (1:1 scale) and in situ inspection, study of residual stress generation, evolution and measurements (hole drilling method both with strain gage rosette and ESPI, X-Ray diffractometer,Barkhausennoise),andmonitoringofelectronicboardandcomponentsby meansofspeckleinterferometry.SheistheScientificDirectoroftheLaboratoryofStatic and Dynamic tests, the Laboratory of Residual Stresses, the Laboratory of Experimental StressAnalysis,theLaboratoryEMILIA(ExperimentalMechanicsIntegratedLaboratory In Aerospace), and the Laboratory of Telemetry at Politecnico di Bari. GiovanniPappalettera isanAssociateProfessoratPolitecnicodiBariwhereheisalsoa lecturerattheBachelorandMasterDegreeofIndustrialDesignandattheMasterDegree of Mechanical Engineering. His main research interests are connected with material characterization and experimental mechanics including optical methods, acoustic emis- sion, and residual stress analysis. He is a member of the Ph.D. committee in Mechanical and Management Engineering at Politecnico di Bari. He is the author of more than one hundred papers published in international journals and conference proceedings and is vii viii About theAuthors co-inventorofthreepatents.Heistheco-authoroftwobooksandmemberofinternational associations including the Society of Experimental Mechanics and the European Society of Experimental Mechanics. VimalathithanParamsamyKannan isaResearcheratPolitecnicodiBari,Italy,where he obtained his Ph.D. degree with honours in 2021. His research interests include Mechanical Characterization of Engineering Materials through Non-destructive Evalua- tiontechniques,particularlyAcousticEmissiontechnique.Healsohasaspecialinterestin theCharacterizationofPolymer-based CompositeMaterials. Hehaspublished morethan 30 articles in international conferences and peer-reviewed journals onAcoustic Emission technique. What is Sound? 1 Whether it is a symphony of Mozart from a stein piano or an unpleasant noise from a pneumatic drill, both are recognized as sound. But what may be the definition of sound? Soundisawave,indeed,becauseittransmitsenergyfromoneplacetoanotherbymeans of a medium but the medium itself is not transported. Hence, before we search for the definitionofsound,letustakeamomenttodiscussthedefinitionofawave.Awaveisa self-sustainingdisturbanceofamedium.Itcanbesimplydefinedasadisturbanceofsome kindorachangeinequilibrium.Whenthisdisturbanceoccursintheambientpressureor the density, we perceive the sound wave. Therefore, sound is the disturbance of ambient pressure, that we receive through our ears and perceive by our auditory system. 1.1 Perception of Sound How do we perceive sound? Human auditory system is nothing more than an advanced and integrated signal processing system. Figure 1.1 shows the section of a human ear. A human or an animal auditory system has ear canal, which ends at the tympanic membrane (or simply known as ear drum). The tympanic membrane is connected to the inner ear through a mechanical linkage of three bones: malleus, incus, and stapes. These mechanical linkages are connected to a liquid filled organ cochlea. When a sound wave reaches our ear, the disturbances pass through the ear canal and vibrates the three bones. The vibrations of these bones over cochlea generates signals for the brain, which pro- cesses these nerve signals as sound. Consider it similar to the functioning of a telegram. Now, we consider a microphone, which is one of the other mechanical systems com- monlyusedforperceivingsound.Itworksonthesameprincipleofvibration/fluctuations ©The Author(s), underexclusive license to SpringerNature SwitzerlandAG2023 1 C. Barile et al.,SoundWaves andAcoustic Emission,Synthesis Lectures onWave Phenomena inthe Physical Sciences, https://doi.org/10.1007/978-3-031-23789-8_1 2 1 WhatisSound? Fig. 1.1 Human auditory system (taken fromWikipedia) duetothepressuredisturbances.Themechanicalresponseofthepressuredisturbancesdue tosound isconverted into electrical signals via capacitors ora piezoelectric crystal. 1.2 How Does Sound Travel? Sofar,wehaveseenhowthesoundisperceivedbuthowdoesthesoundtravel?Atypical wave, with respect to the propagating direction, travels either as a longitudinal or a transverse wave. In simple terms, the difference between longitudinal and transverse wavescanbeexplainedbyonekeyfeature.Inlongitudinalwaves,thedisturbancesoccur only in one direction, which is the direction of the wave propagation. Whereas in transversewave,thereisaninfinitenumberofdirections,alllyinginaplanenormaltothe direction of propagation, the disturbances can occur as shown in Fig. 1.2a. Longitudinal waves propagate through the compression and rarefaction in the propagating medium, as shown in Fig. 1.2b. By definition, sound waves propagate by the compression and rar- efaction of pressure, density or particle displaced in all fluids. Therefore, in most cases, soundtravelsasalongitudinalwave.However,soundcantravelasbothlongitudinaland transverse waves in solids, which will discuss later in detail. ConsidertheblackdotsinFig. 1.2basairmolecules,andwecanassociatethefigureto the propagation of sound. It is worth repeating that the sound wave propagates by the displacement of pressure in the air molecules. So obviously, sound needs molecules for travel. Not surprisingly, sound does not travel in near-empty regions of space. In space, eveniftwoastronautsarefloatingnexttoeachother,theironlywayofcommunicationis radio devices (or sign language).
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