Reasearch On Health Detection Of Composite Laminates By Using Single-mode Ultrasonic Lamb Wave Technique

Composite materials are applied extensively in many pivotal fields such asaerospace, wind power, automobile and so on because of the advantages of highspecific strength, large specific stiffness and light weight. However, appearances ofany damage or defect from the composite materials are great threats to state propertyand the safety of people. Therefore, it is very urgent and necessary to develop a kindof technique which can detect health condition of composite structures fastly. In thispaper, ultrasonic Lamb wave technique is used to detect T300/QY8911compositelaminates with stimulated damages. The combination of Chirp excitation and ellipseimaging is applied to defect imaging in T300/QY8911composite laminate and areinvestigated and eventually imaging and localization of the stimulated damage areachieved successfully. The Major research works and conclusions are outlined asfollows:(1) Chirp signal is investigated to be the excitation signal in ultrasonic Lambwave detection. By Chirp excitation, the responses are post-processed to extract easilyequivalent Tone burst responses which center frequencies are in the range ofbandwidth of chirp excitation so that greatly increase detection efficiency, meanwhileensuring the consistensies of detection conditions.(2) Three kinds of methods that Lamb wave modes can be purificated andsimplified are studied. Firstly two identical piezoelectric wafers are attached on thesame positions both surfaces of a plate. They are applied voltage signals whichamplitudes and phases are the same completely for exciting single S0mode. Inversely,single A0mode can be obtained when the phases of voltage signals are opposite whiletheir amplitudes are kept to be same. The second method is double piezoelectricwafers receiving. According to wave structures of Lamb waves, as the receivers, twopiezoelectric wafers are supposed to be attached on both sides of a plate in the samelocation. The signals received by piezoelectric wafers are summed to obtain single S0mode, and are subtracted to obtain single A0mode. Finally two kinds of piezoelectrictransducers optimized and designed for the ultrasonic Lamb wave detection system.The cylinder-type piezoelectric transducers which are added radial vibration absorption layers and impedance matching layers can stimulate single A0mode in lowfrequency range. Single S0mode can be achieved from the ring-type piezoelectrictransducers.(3) Defect imaging based on ellipse imaging algorithm of single-mode ultrasonicLamb wave technique for isotropic and anisotropicplates is investigated. Sparsepiezoelectric transducer array is attached on tested plates. An aluminum magnesiumalloy cylinder is affixed to T300/QY8911composite laminate by epoxy-resinadhesive to be a simulated damage. A large amount of detection signals obtained bythe many transducer pairs are processed utilizing ellipse imaging algorithms. Theresults show that it is successful to achieve imaging localizing detection of thestimulated damage in T300/QY8911composite laminate and PMMA plate.