Research On Stress Measurements Of Metal Materials Based On Acoustic Microscopy

With the development of technology,high-end manufacturing equipment become more complicated,and the new materials are applied in the industry widely,puts forward more strict requirements for the reliability of the equipment.Residual stress are widely occurred within the material and it can be critical to the mechanical property and dimensional stability of some mechanical structures.In order to evaluate the working condition and service life of component,measurement of the residual stresses levels within that component is crucial.For the key component under the high-load,it’s also important to monitor magnitude of applied stress.It is usually necessary to adopt non-destructive testing for measurement of the stresses levels of engineering materials.Ultrasonic methods have the characteristics of non-destructive,fast,online,and become the focus of research at home and abroad.The accuracy of the measurement system has a crucial effect on the measurement results for ultrasonic methods.In this project,based on acoustic microscopy technique,theoretical and experimental investigation are carried out on the acoustic characteristics of semi-infinite,sheet,coating materials of stress state by using the high-precision acoustic microscopy measurement system and line focus PVDF transducer,the main contents are as follows:(1)Theoretical research is carried out about the mechanical property of hyperelastic material.Combined with the theory of acoustoelasticity,theoretical wave motion model of isotropic materials with stress is established,then the constitutive equation between stress and acoustic propagation is obtained.Also,the surface wave and Lamb wave propagation characteristics of semi-infinite,sheet,coating materials under stress are analyzed.Which is the theoretical foundation for experimental measurement and inversion method of stress.(2)Based on acoustic microscopy,a experiment system for measurement of stress was built.The surface wave velocities with different applied stresses and angles of semi-infinite metal material and polymethyl methacrylate are measured by the acoustic microscopy system,then the relationship between stress and surface wave velocity is obtained.The surface wave velocity distribution of the metal welding specimen at different positions are obtained by using the 2-D scanning method,then the residual stress distribution can be measured based on the theory of acoustoelastic surface wave,which provides a new detection technique for measurement of residual stress of material.(3)The dispersion curves of Lamb wave of aluminum sheet are measured based on the acoustic microscopy system,then the effect of stress on the phase velocity of Lamb wave are studied.The experimental results agree with the theoretical counterparts,which verifies the correctness of the theoretical model.The multi-parameter inversion method is used for the measurements of stress of sheet,the experimental data of aluminum sheet seen as the inversion target and the multi-parameter inversion model and the objective function are established by the theoretical wave motion model.Inversion of stress and elastic constants of aluminum sheet by using the particle swarm optimization based on simulated annealing(PSO-b-SA).Furthermore,the wave velocity variation of the coating half-space material and coating plate under different stress states are also measured by acoustic microscopy system and the influence of stress on the phase velocity of the coating was analyzed,This research laid the foundation for measurement of the stress of the coating structure material.