为揭示超声红外热成像检测中缺陷区域的生热机理，考虑预紧力对缺陷生热的影响，采用裂纹试件开展了预紧力分别为100、150、200 N的检测试验，发现裂纹区域温度与预紧力正相关，裂纹两端的生热量明显高于裂纹中段，尖端热斑最明显，且不同预紧力下圆形热斑最明亮。基于单自由度有阻尼位移激励系统和热源温度场叠加法建立了超声激励下裂纹生热的简易数学模型，通过计算参考点P■和裂纹尖端点P■的温度变化，发现P■点温度变化与试验结果一致，随着预紧力增大，P■点的计算结果与试验温升曲线拟合误差减小，且温升速率变化逐渐趋于一致。该模型能够较好地描述裂纹的生热过程，为超声红外热成像检测的加载参数优化提供了模型基础，具有一定的理论意义与工程价值。

复杂型面叶片由于其结构复杂, 缺陷检测困难, 针对这类叶片的无损检测研究一直是国内外关注的热点。文中基于超声激励下含缺陷介质的摩擦生热模型, 分析缺陷处的热流传导, 推导了含裂纹叶片简化模型的表面温度场。针对复杂型面叶片裂纹处的生热模型, 应用有限元方法进行了数值仿真。仿真结果表明, 激励时间越长, 裂纹缺陷区域温升越大; 温升速率随时间增加呈先上升后下降的趋势。利用超声红外热成像检测平台, 对含裂纹的汽轮机叶片进行检测。实验结果表明, 当预紧力处于100~150 N时, 裂纹区域生热最明显, 叶片裂纹检测效果最好。基于数值仿真和实验表明, 超声红外热成像技术可以有效地检测出复杂型面叶片中的裂纹缺陷,具有一定的工程指导意义和广泛应用前景。

Aiming at the drawbacks of low contrast and high noise in the thermal images, a novel method based on the combination of the thermal image sequence reconstruction and the first-order differential processing is proposed in this work, which is comprised of the following procedures. Firstly, the specimen with four fabricated defects with different sizes is detected by using pulsed infrared thermography. Then, a piecewise fitting based method is proposed to reconstruct the thermal image sequence to compress the data and remove the temporal noise of each pixel in the thermal image. Finally, the first-order differential processing based method is proposed to enhance the contrast. An experimental investigation into the specimen containing de-bond defects between the steel and the heat insulation layer is carried out to validate the effectiveness of the proposed method via the above procedures. The obtained results show that the proposed method can remove the noise, enhance the contrast, and even compress the data reaching at 99.1%, thus improving the detectability of pulsed infrared thermography on metal defects.