Numerical simulation on damage assessment of micro cracks by ultrasonic nonlinearity
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摘要: 材料早期力学性能退化总是伴随着某种形式的材料非线性力学行为，从而导致超声非线性特征，即高频谐波的产生。建立长度小于半波长的随机分布微裂纹群模型以描述材料早期损伤状态，计算了微裂纹群超声非线性特征，分析了衍射效应对超声非线性特征的影响。计算结果表明，在早期损伤几乎未对材料性能造成影响的情况下，检测信号已经表现出明显非线性特征；随着裂纹数量的增加，二次声源叠加产生更为复杂的频率成分，显著影响超声非线性特征。研究工作可为材料早期损伤评价提供技术支撑。Abstract: Degradation of material mechanical properties in the early stage is always accompanied by some form of non-linear mechanical behavior, which leads to the generation of high-frequency harmonics. In this paper, the model of randomly distributed micro cracks with length less than half wavelength is established to describe the early damage of material. The ultrasonic nonlinear characterization of the micro cracks is calculated, and the influence of diffraction effect on the ultrasonic nonlinear characterization is analyzed. The results show that the detection signal has obvious nonlinear characteristics when the early damage hardly affects the material property, besides, as the number of cracks increases, the superposition of secondary sources produces more complex frequency components, which significantly affects the non-linear characteristics. The research work provides technical support for early damage assessment of materials.
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