Abstract
Residual stress has significant influence on the performance of mechanical components, and the nondestructive estimation of residual stress is always a difficult problem. This study applies the relative nonlinear coefficient of critical refraction longitudinal (LCR) wave to nondestructively characterize the stress state of materials; the feasibility of residual stress estimation using the nonlinear property of LCR wave is verified. The nonlinear ultrasonic measurements based on LCR wave are conducted on components with known stress state to calculate the relative nonlinear coefficient. Experimental results indicate that the relative nonlinear coefficient monotonically increases with prestress and the increment of relative nonlinear coefficient is about 80%, while the wave velocity only decreases about 0.2%. The sensitivity of the relative nonlinear coefficient for stress is much higher than wave velocity. Furthermore, the dependence between the relative nonlinear coefficient and deformation state of components is found. The stress detection resolution based on the nonlinear property of LCR wave is 10 MPa, which has higher resolution than wave velocity. These results demonstrate that the nonlinear property of LCR wave is more suitable for stress characterization than wave velocity, and this quantitative information could be used for residual stress estimation.
Highlights
Residual stress is an inherent stress which keeps the stress balance in the inner material when the mechanical components are unaffected by external strength
The nonlinearity property of LCR wave is proposed to nondestructively characterize and evaluate the stress state of metal material, the dependence between the stress level and the relative nonlinear coefficient is investigated, and the feasibility of residual stress estimation based on the nonlinearity property of LCR wave is verified
The wave velocity decreases only about 0.2%, and that is because the dislocation structures evolution and microplastic deformation would not induce the significant change in wave velocity
Summary
Residual stress is an inherent stress which keeps the stress balance in the inner material when the mechanical components are unaffected by external strength. Residual stress measurement methods could be categorized into destructive and nondestructive methods [1]. TSA is a noncontacting and sensitive experimental stress analysis technique [6, 7], which provides full-field stress data over the surface of a cyclically loaded specimen or component [8]. The stress diagram of the whole component or a certain part can be obtained, which only requires few surface preparations and does not need further data processing. This technique merely provides information on the surface stress field in structures. The ultrasonic method has the characteristics of high resolution, high penetration, and no harm to human body; it is one of the most promising nondestructive measuring methods
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