This paper reports a numerical study of the sensitivity and applicability of the Nonlinear Coda Wave Interferometry (NCWI) method in a heterogeneous material with a localized microcracked zone. We model the influence of a strong pump wave on the localized microcracked zone as a small average increase in the length of each crack. Further probing of this microcracked zone with a multiply scattered ultrasonic wave induces small changes to the coda-type signal, which are quantified with coda wave interferometry. A parametric sensitivity study of the CWI observables with respect to the changes in crack length is established via numerical simulations of the problem using a 2D spectral element method (SEM2D). The stretching of the signal, proportional to the relative variation in effective velocity, is found to be linearly proportional to the global change in crack length, while the other CWI parameter, the remnant decorrelation coefficient, is found to be quadratically proportional to the crack length change. The NCWI method is shown to be relevant for the detection of different damaged material states in complex solids. The reported numerical results are especially significant in the context of quantitative nondestructive evaluation of micro-damage level of a heterogeneous materials using nonlinear ultrasound signals.

本文报告了非线性尾波干涉测量 (NCWI) 方法在具有局部微裂纹区域的异质材料中的灵敏度和适用性的数值研究。我们将强泵浦波对局部微裂纹区域的影响建模为每个裂纹长度的平均小幅增加。用多重散射超声波进一步探测该微裂纹区域会引起尾波型信号的微小变化，这些变化可以通过尾波干涉测量法进行量化。使用二维谱元法 (SEM2D) 对问题进行数值模拟，建立了 CWI 可观测量相对于裂纹长度变化的参数敏感性研究。信号的拉伸与有效速度的相对变化成正比，与裂纹长度的全局变化成线性正比，而另一个 CWI 参数，即剩余去相关系数，与裂纹长度成二次方正比改变。 NCWI 方法被证明适用于复杂固体中不同受损材料状态的检测。所报告的数值结果在使用非线性超声信号对异质材料的微损伤水平进行定量无损评估的背景下尤其重要。