钛合金蜂窝结构蒙皮脱焊缺陷锁相红外热成像检测

蒙皮脱焊是钛合金蜂窝结构制造和服役过程中最常见的缺陷类型。受钛合金材料热导率低的影响，钛合金蜂窝结构中蒙皮越厚，红外热成像检测时其表面反映脱焊缺陷信息的温度差异信号就越弱，检测难度就越大。针对这一问题，研究了不同蒙皮厚度钛合金蜂窝结构锁相红外热成像检测时调制频率的选取范围。建立了钛合金蜂窝结构锁相红外热成像检测有限元模型，分析了蒙皮表面温度在调制热流作用下的变化历程，基于相关算法提取了蒙皮表面对应缺陷区和非缺陷区的相位差，分析了相位差与调制频率、蒙皮厚度的关系。利用锁相红外热成像检测系统对预制脱焊缺陷的蜂窝试件进行了实验研究，获得了缺陷区与非缺陷区信号相位差与调制频率的关系。研究结果表明，针对蒙皮厚度为0.6~2.0 mm的钛合金蜂窝结构，采用0.04~0.10 Hz的调制频率能够获得最佳检测结果。研究结果为钛合金蜂窝结构实际检测提供了工艺指导。 

Detection of skin desoldering defect in Ti-alloy honeycomb structure using lock-in infrared thermography test

Skin desoldering is the most common defect of Ti-alloy honeycomb sandwich during manufacturing and serving period. Due to low thermal conductivity of Ti-alloy material, as the skin of Ti-alloy honeycomb sandwich becomes thicker, temperature signal difference of defect and non-defect becomes weaker, and thus it is more difficult to test the defect by infrared thermography. Given the problem, the range of modulation frequency in this structure with different skin thickness by lock-in infrared thermography was studied. The finite element simulation model was built to analyze the variation of surface temperature under the heat flow. The extracted phase differences of defect and non-defect area based on correlation algorithm are available to analyze the effect of modulation frequency and skin thickness on these phase differences. Experiments were performed on the specimen with prefabricated defects of this structure using lock-in infrared detection system. The relationship between the phase difference and the modulation frequency was given after extracting the phase of defect and non-defect area. The research results show that the 0.04-0.10 Hz modulation frequencies applied to detect this structure of skin thickness within 0.6-2.0 mm can get optimal results. Research results provide a technical guidance for the practical detection of Ti-alloy honeycomb sandwich structure.