非线性激光超声裂纹检测技术的核心是使用机械/光热加载的方式在裂纹上施加载荷,使裂纹实现周期性开合。针对关于这一裂纹闭合机理研究较少的问题,在加热激光辐照区域内,使用时域激光超声方法对真实微裂纹的闭合响应及裂纹闭合引起的裂纹局部塑性/弹性微观变化进行研究。通过分析各模态超声波在裂纹不同闭合状态下的峰峰值、到达时间变化,可以获得裂纹闭合的相关信息。结果表明,信号峰峰值和到达时间的变化过程与裂纹闭合出现的早晚有关,裂纹闭合出现早晚的顺序与裂纹宽度对应。

The core of nonlinear laser ultrasonic crack detection technology involves the use of a mechanical/photo-thermal loading method to induce loading on cracks, thereby enabling periodic opening and closing of these cracks. The crack closure mechanism has rarely been investigated. To address this issue, in the heated laser irradiation area, the time domain laser ultrasonic method is used to study the closing response of real micro-cracks. The local plastic/elastic microscopic changes induced by the crack closure are also investigated. Analysis of the changes in the peak-peak value and arrival time of each ultrasonic mode in different crack closing states yield pertinent information about the crack closure process. The results reveal that the change process of the signal peak-peak value and arrival time is related to the time of crack closure, and the sequence of crack closure corresponds to the crack width.