Research On Laser Ultrasonic Detection Technology Of Rough Surface Contact State

The contact surface is a rough surface with specific surface morphology and cross scale characteristics.The joint surface will undergo complex small deformation after loading,and its contact behavior has an important influence on the Friction and wear characteristics,electric and thermal conductivity and lubrication performance of the parts.Because the contact area is too close,the traditional means of contact measurement cannot be applied,and new measuring means are needed.In this paper,a method of measuring the contact state of the surface based on the laser-generated surface acoustic wave(SAW)is studied.A joint surface detection system based on laser ultrasonic technology is designed to study the relationship between the surface acoustic wave single and other contact state parameters,such as surface load,nominal contact area and surface roughness.First of all,the theory of laser ultrasound and the difference between the thermal elastic mechanism and the corrosion mechanism are discussed and analyzed to study the propagation characteristic of surface acoustic wave.Then,the influence of the laser beam pulse energy,the shape and size of the laser beam on the surface acoustic wave signal is studied,and the parameter setting of the laser beam is optimized.Secondly,a finite element model of laser radiation aluminum material is established.Through thermal elastic coupling simulation and structural dynamics simulation,the change cloud chart of material temperature field,stress field and displacement field are got,and the simulation results conform to the theoretical model of laser ultrasound.Thirdly,the difference of absorptivity of laser energy by different materials and attenuation characteristics in the process of acoustic surface propagation is investigated.Then,a simplified two-dimensional rough contact model based on fractal theory is established,and the contact behavior of the surface convex bodies is simulated.The theory that the passing rate of the surface acoustic wave is affected by the real contact area is put forward on the basis of the simulation results.Finally,the laser ultrasonic detection system of the contact state of the interface is set up,and orthogonal experiment and single factor experiment is designed to investigate the effects of surface load,nominal contact area and surface roughness on surface acoustic wave.The experimental results illustrate that the passing rate of the surface acoustic wave is related to the real contact area.The greater the real contact area,the stronger the surface acoustic wave signal.Besides,the actual contact area is positively correlated with surface load and nominal contact area,and is negatively correlated with surface roughness.The research results can offer the theoretical and experimental foundation for the theoretical and numerical simulation of laser ultrasound,the study of rough joint surface contact state and laser nondestructive testing.