The ultrasonic nonlinearity parameter derived for one-dimensional propagation of a longitudinal wave in an isotropic material has been considered useful in the evaluation of material degradation. To demonstrate this, many researchers have reported on the correlation with the yield strength obtained from a tensile test. However, there is an essential issue with this procedure - which is that the ultrasonic nonlinearity parameter is derived in a state where the lateral strain is restrained, whereas the tensile test to measure the yield strength is carried out under uniaxial stress conditions, where lateral deformation is free. In this study, to address this issue, the authors have defined the ultrasonic nonlinearity parameter under uniaxial stress conditions which were the same as the tensile test, and showed that the correlation with the yield strength was higher than the currently used ultrasonic nonlinearity parameter. To verify the validity of the proposed ultrasonic nonlinearity parameter, experiments were carried out for Al6061-T6 alloy specimens heat-treated with different aging times. Results showed that the proposed ultrasonic nonlinearity parameter exhibited a much higher correlation with yield strength than the currently used nonlinearity parameter.

中文翻译：

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单轴应力条件下的超声非线性参数

为纵波在各向同性材料中的一维传播而导出的超声非线性参数已被认为可用于评估材料退化。为了证明这一点，许多研究人员报告了与从拉伸试验中获得的屈服强度的相关性。然而，这个程序有一个基本问题——超声波非线性参数是在横向应变受到限制的状态下导出的，而测量屈服强度的拉伸试验是在单轴应力条件下进行的，其中横向变形免费。在这项研究中，为了解决这个问题，作者定义了与拉伸试验相同的单轴应力条件下的超声非线性参数，并表明与屈服强度的相关性高于目前使用的超声非线性参数。为了验证所提出的超声非线性参数的有效性，对不同时效时间热处理的 Al6061-T6 合金试样进行了实验。结果表明，与当前使用的非线性参数相比，所提出的超声非线性参数与屈服强度的相关性要高得多。