Research On Testing Method Of Reinforcement Width By Laser Ultrasonic C-Scan

With the increase of requirements for lightweight design of industrial technology,the reinforcement structures are applied more and more widely.The width of reinforcement is one of the main factors affecting the performance of reinforcements.Therefore,it is very important to determine the width of reinforcements on the online equipment for evaluating of the reinforcement strength quickly and accurately.Recently,laser ultrasound technology has become an emerging non-destructive testing technology,and owns many advantages such as non-destructive,non-contact,wide bandwidth of frequency,high resolution,real-time.Moreover,laser ultrasound technology is suitable for testing defects in special environments.In this paper,the laser ultrasonic C-scan technology is used for testing the width of reinforcements on 304 stainless steel plates.The research topic mainly contains four aspects.Firstly,this paper introduces the basic theory of the laser ultrasonic.The excitation principle of the thermoelastic mechanism for the laser ultrasound is studied in detail.In addition,we discuss the modes of ultrasonic waves excited under the thermoelastic mechanism and their propagation characteristics.Then we briefly summarize the propagation characteristics of ultrasonic waves excited under different types of excitation sources,and the detection methods of laser ultrasound.The propagation process of laser ultrasound in 304 stainless steel plate is simulated by the finite element method.We calculate the temperature fields and the displacement fields of laser ultrasound in a 304 stainless steel plate.Secondly,the laser ultrasonic C-scan detection system is built.The transmitter excites a pulsed laser on the steel plate,then the ultrasonic waves are received by the interferometer,and then the measured object is moved by the automatic stage.The measured object can be tested by the laser ultrasonic C scan.Then,the width of reinforcements are measured by the laser ultrasonic C-scan.The distribution of the ultrasonic field excited by a pulsed laser on 2 mm thick 304 stainless steel plates are analyzed through theoretical method.The experimental results are compared with the theoretical calculation results.The experimental results show that the amplitude of the reflected transverse wave is higher than that of the reflected longitudinal wave,when the distance between the excitation point and the receiving point is 4 mm.The amplitude of the reflected transverse wave can be used as the characteristic signal for testing the width of reinforcements by the laser ultrasonic Cscan.Finally,the measuring accuracy is improved by data processing methods.The laser ultrasound signals and laser ultrasound C-scan images are processed by using wavelet noise reduction and image mean filtering.The results show that the wavelet noise reduction can effectively improve the signal-to-noise ratio of signals.The absolute errors between the values obtained by laser ultrasound C-scan and the actual width are less than 0.05 mm.The width of reinforcements can be tested by the laser ultrasonic C-scan quickly and contactless.This paper provides an experimental research basis for further characterizing the strength of reinforcements.