Research On Measurement Method Of Elastic Modulus Of Plates By Laser Ultrasonic

Manufacturing process of plate is simple,so many materials,such as gold,silver,copper,zinc,iron,etc.,can be made into plates which are more and more widely used in various industries.Many scholars have studied the mechanical properties of plates from many aspects,such as strength,rigidity,hardness and fatigue life.The elastic modulus is one of the important indexes of the material mechanical properties,which represents the comprehensive situation of the material mechanical properties.In order to measure the elastic modulus of plates quickly,accurately and non-destructively,a method based on laser ultrasound is proposed in this paper.This method can overcome the shortcomings of traditional methods that can not be applied to the harsh environment,and realize the non-contact measurement of the elastic modulus of plates.This paper discusses the laser ultrasonic measurement of the elastic modulus of plates from the following aspects.Firstly,the theoretical basis of laser ultrasound is introduced.The thermoelastic mechanism used in this paper is described in detail.And this paper describes the basic characteristics and the main application of ultrasonic modes,and then introduces the receiving methods and the signal processing methods of laser ultrasonic.These studies lay a theoretical foundation for the subsequent measurement of elastic modulus of thick plates and foils.Secondly,the laser ultrasonic detection system is built.It mainly includes three parts:the laser excitation part,which mainly excites the ultrasonic wave in the plate;the interferometer receiving part,which receives the ultrasonic wave;the moving part,which realizes the accurate movement of the detection plate.Thirdly,the laser ultrasonic measurement of the elastic modulus of thick plates is realized.Two groups of samples used in the experiment are introduced,aluminum alloy plate and magnesium lithium alloy plate.The relationship between the propagation distance and the propagation time of ultrasonic modes in the aluminum alloy 6061 plate with a thickness of 5 mm is analyzed theoretically,and the correctness of the theorical results is verified by experiments.The propagation velocity of longitudinal waves and surface waves in the plate are obtained,and the elastic modulus of the thick plates are measured by laser ultrasonic.Finally,the elastic modulus of foils is measured by the laser ultrasonic.The samples of aluminum alloy foils and magnesium lithium alloy foils are introduced.The propagation characteristics and dispersion curve of Lamb wave are analyzed theoretically.The S₀ mode propagation velocity of Lamb wave is obtained by experiments and then taken into the program of exhaustive method to get the elastic modulus of foil inversely.