外文原文-空气耦合超声：模拟和实验研究复合材料衬垫.pdf

1、Proceedings of the National Seminar&Exhibitionon Non-Destructive EvaluationNDE 2009,December 10-12,2009401Air-Coupled Ultrasonics:Modelling and Experimental Studiesfor Thick Composite LinersP.Karthikeyana,S.Hari Krishnaa,N.Narayanankuttya,E.J.Francisa and Krishnan BalasubramaniambaCCQG,Composites En

2、tity,Vikram Sarabhai Space Centre,Trivandrum-695013bCentre for NDE and Dept.of Mechanical Engineering,IIT Madras,Chennai-600036AbstractComposite materials have gained importance in various fields because of their properties like higher specific strength,higher specific stiffness,corrosion resistance

3、 etc.They are used as ablative nozzle liners in aerospace sector for functioning under high thermal and erosiveenvironments.Quality assurance is very important for these composite liners,being critical components of launch vehicles and rockets.Defectslike delaminations,low density regions can signif

4、icantly change the erosion rate of these liners thereby leading to mission failure.Till now,radiography testing(RT)has been the primary NDT technique for composite liners.Thicker and larger diameter nozzle liners need very highenergy for taking tangential radiography thereby necessitating linear acc

5、elerators.Ultrasonic testing(UT)is introduced with the aim ofreducing/replacing radiographic testing.UT using liquid couplant is to be avoided while testing because of the porous nature of these compositeliners,as the liquid couplant may ingress inside the liner thereby affecting performance and fur

6、ther processing.In this paper,the application of air-coupled ultrasonic system for the NDT of nozzle liners using through transmission mode is discussed.Air-coupled Ultrasonics is an emerging non-contact ultrasonic technique which avoids the physical contact between the transducer and materialbeing

7、tested.The transducers and equipment are designed to reduce the energy losses occurring due to acoustic impedance mismatches.Finiteelement analysis is performed using the general-purpose finite element package-ABAQUS to simulate the wave propagation in compositeswith air-coupling and to study the in

8、teraction of wave with defects in composites.Experimental studies are carried out on composite specimens.A specially designed seven axis manipulator system is used for the quick scanning of the nozzle liners with air-coupled transducers.Keywords:Air-coupled Ultrasonics,Ablative nozzle liners,Through

9、-transmission mode.2.Feasibility of ultrasonic testing on Ablativecomposite linersUltrasonic testing operates based upon wave-materialinteraction phenomena and is an established method of non-destructive testing.By propagating a wave in a givenmedium,information about the medium can be obtainedanaly

10、zing the transmitted or reflected signals.Ultrasonics areused to detect variations in structure,presence of cracks orother physical discontinuities,measure the thickness ofmaterials and coatings and determining other characteristicsof industrial products.It is used to locate criticaldiscontinuities

11、such as delaminations and debonds incomposite products.2.1 Conventional Ultrasonics with liquid couplant:Conventional UT with liquid couplant may be conductedeither by the pulse-echo technique or the throughtransmission technique.Pulse echo technique uses a singletransducer.A flaw is indicated by th

12、e presence of a reflectedsignal ahead of the back wall echo.Through-transmissiontechnique uses two transducers,with the transmitter on oneside and the receiver on the other side of the componentunder test.A flaw is indicated by the reduction or absenceof a transmitted signal.It also gives very good

13、sensitivitybut needs access on both sides of the component and perfect1.IntroductionComposite materials are increasingly being used in manyapplications.They offer many advantages such as specificstrength,specific stiffness,directional tailorability etc.andare the preferred ones for the structural ap

14、plications.Becauseof their thermal,ablative and fire retardant properties,theyare used in applications such as ablative nozzle liners forfunctioning under very high thermal and erosiveenvironments.Generally ablative composites are used in thenozzles of solid motor of a rocket or a launch vehicle tos

15、ustain the high temperature and velocity of the combustiongases.Silica phenolic and carbon phenolic composites arecommonly used for making nozzle liners.In this paper,the application of air-coupled ultrasonicsystem for the NDT of nozzle liners using throughtransmission mode is discussed.Modelling an

16、d simulation isdone using general purpose Finite Element package,ABAQUS for the generation of waves in composite materialwith air-coupling and to study the interaction of the wavewith defect in composites.The simulation results arequalitatively compared with that of experiments.Theapplication of air-coupled ultrasonic system for the NDT ofnozzle liners using through transmission mode is presented.Defect detected with air-coupled through transmission modeare compared with that of radiography and