裂纹尖端塑性区非线性超声混频定位表征

基于非共线体波混频的方法,本文对金属材料中裂纹尖端的塑性变形区开展定位表征研究。基于二阶微扰理论和矢量分析方法,理论研究非共线体波混频的共振条件及其定位塑性变形区的机理。有限元仿真表明,两横波混频产生的纵波可用于定位塑性变形区。以A17075-T6材料为检测对象,通过实验证明两列横波混频定位裂纹尖端塑性区的可行性。实验中分别选取中心频率为5 MHz-5 MHz的两列横波和4.75 MHz-55.25 MHz的两列横波作为基波,利用非线性超声混频参量定位表征裂纹尖端的塑性变形区。研究结果表明两种频率对产生的非线性超声混频参量峰值区域与试样中塑性区位置吻合度比较好,可以看出非线性超声混频方法能够比较有效地定位金属裂纹尖端塑性区。 

Localization of the plasticity at crack tips using the non-collinear wave mixing

A method of the non-collinear wave mixing was adopted to localize the plasticity at the crack tips.For the nonlinear mixing of the bulk waves,the resonance conditions were theoretically investigated based on the perturbation approach and vector analysis.It is numerically demonstrated that the longitudinal wave generated by the non-collinear mixing of the shear waves is sensitive to the plastic zone.In addition,experimental investigations were conducted for localizing the plasticity at the crack tips in the specimens of 7075-T6 aluminum alloy.Two pairs of shear waves with the frequencies of 5 MHz-5 MHz and 4.75 MHz-5.25 MHz,were selected as the primary waves,respectively.The acoustic nonlinear parameters were utilized to characterize the plasticity state at the crack tips.It is illustrated that the maximums of the acoustic nonlinear parameters occur at the areas ahead of the notch,which exactly are the plastic zones around the crack tips.Therefore,the non-collinear wave mixing may be a potential way to locate the plasticity at the crack tips.