Study On The Detection Method Of Aluminum Defects By Two-point Excitation Laser Ultrasonic Based On Synthetic Aperture Focused SAFT

At present,ultrasonic testing is generally used to detect the defects of aluminum products in industrial production.But the traditional laser ultrasonic testing technology mainly relies on the coupling agent to couple the ultrasonic transducer with the test sample.If the shape of the test sample is complex,it can’t meet this requirement,so the traditional ultrasonic testing method has some limitations.As a non-contact ultrasonic testing method,laser ultrasound does not need coupling agent,and can be competent for the detection of complex surface samples.In particular,laser ultrasound and synthetic aperture focusing imaging technology are combined to image the internal defects of samples.However,the previous laser ultrasonic SAFT detection technology mostly uses single point excitation single point scanning,which needs a lot of time to detect the internal defects of samples.In order to improve the work efficiency and reduce the scanning time,this paper proposes a two-point excitation two-point scanning method,and studies its feasibility in theory.Firstly,the physical model of ultrasonic wave excited by laser in aluminum block is established,and the propagation mechanism of ultrasonic S-wave,P-wave and surface wave excited in aluminum block under thermoelastic mechanism is analyzed.The whole field acoustic diagram of laser ultrasonic wave in aluminum block is simulated by using finite element method,and the propagation directivity of S-wave,P-wave and surface wave is expounded,which verifies the correctness of the model and provides reference for subsequent research the simulation foundation is established.The basic principle of two-point excitation laser ultrasonic SAFT is given,and the imaging algorithm of two-point excitation laser ultrasonic SAFT is obtained.Secondly,two-point excitation laser ultrasonic SAFT is used to image the internal defects of aluminum block.According to the characteristics of laser ultrasonic with multi-mode,wide band and directivity,the SAFT algorithm is optimized.According to the results,the feasibility of two-point excitation laser ultrasonic SAFT in detecting the smallest size defects and the ability to distinguish the adjacent defects are discussed.It can improve the recognition ability and imaging resolution of small defects in the detection of defects,reduce the scanning time by half,and significantly improve the detection speed.Finally,based on the two-point excitation laser ultrasonic SAFT detection method,an experimental device of two-point scanning laser ultrasonic detection of aluminum defects is built,which verifies the feasibility of two-point excitation laser ultrasonic SAFT detection method for aluminum defects.