超声红外热像技术中金属平板裂纹的生热特性

超声红外热像技术是一种新型无损检测技术,缺陷区域生热特性的研究有利于最优化检测方案的制定。实验分析表明:超声激励作用于含贯穿裂纹的金属平板时,与激励同侧的裂纹区域温度升高比异侧更明显,但裂纹面总体的生热效率稳定。针对上述实验现象,采用显式有限元方法建立了与实验系统对应的仿真模型,进行了机热耦合分析。在仿真模型中,采用压电-力类比方法模拟超声换能器的逆压电效应,并引入动态松弛模拟预紧力对被测平板初始状态的影响。仿真与实验结果得到了一致的裂纹区域温度分布和裂纹面生热规律,建立了裂纹面生热效率与裂纹面摩擦力及相对运动速度之间的联系,揭示了工具杆和被测平板之间的预紧力使裂纹面接触状态改变是裂纹生热向激励同侧偏移的直接原因。

Heating characteristics of metal plate crack in sonic IR imaging

Sonic infrared imaging is a new kind of hybrid nondestructive testing method. Research on heating characteristics of defect region is propitious to the optimization of testing scheme. Experimental results show that temperature rising of crack region measured at the excitation side is higher than that at the excitation opposite side; however, the heating rate of crack contact surface is stable in the mass. Based on the phenomenon of crack heating under intensive ultrasonic pulse, a finite element model of experimental setup was established and a thermal-stress analysis was performed by an explicit finite element method. In the finite element model, a piezoelectric-force analogy method was employed to simulate inverse piezoelectric effect in the ultrasonic excitation system, and dynamic relaxation was introduced into the simulation in order to cover the effect of engagement force on the initial state of specimen. During the FEM simulation, the crack frictional heating excited by ultrasonic pulse was calculated, and temperature distribution in space and time domain was described. The relationship between friction heating, friction force and relative velocity at contact surface was revealed. Simulated results reveal the engagement force between horn and testing plate makes the heating position in crack surface shift to the excitation side.