Calculation Of The Stress Field On The Surface Of An Obejct Based On Laser Grating Method

The common residual stress in the process of production and machining can affect the service condition of the workpiece and lead to safety hazards during service.Therefore,the accurate measurement of residual stresses is of great importance to ensure the reliability of workpieces and reduce safety risks of the industrial production site.As an emerging NDT technology in recent years,laser ultrasound has been gradually applied to the field of residual stress detection due to its advantages of high spatial and temporal resolution,non-contact detection and the ability to achieve complex object surface detection.This thesis has carried out the simulation research of laser ultrasonic wave velocity measurement method,the establishment of laser ultrasonic stress detection system and the estimation of surface stress field distribution based on stress detection of characteristic points.The main work is as follows.1.A finite element simulation study of the laser ultrasound surface wave velocity measurement method is carried out.Through the numerical analysis of the relationship between wave velocity and stress variation,it is concluded that ultrasonic surface wave is not sensitive to stress variation.On this basis,the finite element method is used to explore the stability and accuracy of different velocity measurement methods on the wave velocity measurement results.The simulation results show that the laser grating method has great advantages in wave velocity measurement,which verifies the feasibility and effectiveness of using laser grating method to measure wave velocity.2.A system for detecting stress on the surface of an object based on the laser grating method is established.The system hardware selection and software design are completed from the perspective of improving the measurement accuracy and optimising the experimental design,the laser ultrasonic stress detection system is built.In the system test,in response to the shortcomings of the signal becoming weak at the position far away from the light source and unable to form a stable grating signal,the improved laser grating method is proposed in combination with the cross-correlation analysis method to solve the problem of limited measurement conditions,improve the accuracy of surface wave velocity measurement results,and realize the optimization of laser ultrasonic stress detection system.3.A method for estimating the stress field distribution on the surface of an object based on feature point stress detection is explored.After realising the calibration of the acoustoelastic coefficient and verification of the accuracy of the measurement results of the laser ultrasonic stress detection system,the method first carried out the detection of the characteristic point stress on the object surface,and then fitted the stress field distribution on the object surface using the regression analysis method to realise the stress field calculation on the object surface.Compared to the traditional mean or scatter plot stress field study methods,the stress field distribution study is more holistic and intuitive,with less error and higher accuracy in the stress calculation.