高温金属构件微裂纹的非线性超声响应行为与检测技术研究

In the aeronautics and astronautics fields, chemical engineering and petroleum plants and nuclear power plants, there are many structural components of metal alloys. Over an extended period of time, these components are exposed to elevated-temperature and subjected to the long-term sustained loading. Under these conditions, the formation of microcrack in these components becomes one of the most critical factors determining the safety operation of them. Due to the increases in operation parameters, it is very necessary to detect the microcrack of metal components using non-linear ultrasonic (NLU) testing. In previous studies, however, there is lack of systematic investigation in the interaction between microcrack and ultrasonic echo waves. Meanwhile, there are many controlled factors, such as the nonlinearity of testing system and different internal defects with NLU properties. Therefore, the present research mainly deals with the detection of microcracks formed during the elevated-temperature creep of metals. Firstly, the detailed observation of these microcracks is employed to study the features of distribution and deformation. Then, the NLU response behavior of microcracks is further clarified by combing the related models. Based on above analyses, the multi-parameter extraction from the related material properties and signal parameters is performed to characterize the microcrack comprehensively. Finally, the reliable detection of microcracks can be achieved by the decision-level fusion method. In addition, there results can be used to ensure the effective maintenance and safety operation of above components.

航空航天、石油化工以及核能发电等领域关键设备中大量金属构件长期服役在高温、高压条件下，致使蠕变形成的微裂纹成为其安全运行的重大隐患。随着服役条件的不断恶化，针对微裂纹的非线性超声检测技术需求日益旺盛。然而，已有研究很少系统分析微裂纹的非线性超声响应行为。同时，超声检测系统的非线性和超声微观缺陷的多样性等因素严重制约了非线性超声技术在微裂纹检测方面的工程应用。因此，本项目拟采用非线性超声技术对高温金属蠕变过程中形成的微裂纹进行系统研究。首先借助相关测试手段对微裂纹进行精细考察，揭示其分布特征与力学形变特点。在此基础上，结合对现有理论模型的深入分析，进一步阐明微裂纹的非线性超声响应行为。随后，通过对非线性超声检测系统综合评价、参数优化及试验方法设计，减弱系统非线性的影响。最后，提出多参数提取的融合识别方法，实现对金属构件微裂纹的精准检测，从而为上述行业关键设备的科学维护和安全运行提供可依据。

航空航天、石油化工以及燃料发电等关键领域中大量金属构件长期服役在高温、高压条件下，蠕变微裂纹的形成将不可避免。随之相关的后续长大过程将进一步加速金属构件性能的劣化进程，甚至威胁到整个设施的正常运转。通常这些微裂纹大多存在于构件内部，不但具有很强的隐蔽性和潜在危害性，而且使用常规方法难以发现。由此可见，为了尽早发现这些微裂纹安全隐患，对其开展的一系列检测技术研究成为了近年来国内外研究的热点之一。. 本项目以典型的P91耐热钢高温蠕变实验为基础，通过非线性超声技术和相关表征手段的联合使用，针对高温蠕变过程中形成的微裂纹及其检测技术展开了深入系统研究。首先，在600℃与620℃条件下分别进行单轴高温拉伸、持久/间断蠕变等多种实验，获得了一系列不同温度和应力水平组合条件下的P91钢完整蠕变曲线和关键数据。同时，通过对非线性超声测量中待测试样形状的合理选取、测试过程中具体环节的优化设计，对比理论计算结果，实现了对P91钢材料自身产生非线性超声系数的有效测量，并阐明了相关表征参数对不同条件下P91钢蠕变状态的响应规律。其次，使用扫描电镜等表征手段，精细考察了实际蠕变过程中微裂纹的形貌特征与分布位置，揭示了蠕变过程中微裂纹的长大动力学行为。随后，结合弹性力学、接触力学以及统计理论，构建了具有统计分布的微裂纹力学形变方程与非线性响应模型。在此基础上，利用多特征参数提取（主要包括材料物性参数和信号时频参数）对非线性超声系数的测量值进行预处理（如修正计算、位错非线性超声系数估算等），成功分离出微裂纹产生的非线性超声系数。最后，分别从力学形变方程、微裂纹非线性响应模型和信号时频分析等方面对微裂纹进行检测，结合D-S证据理论融合算法，实现了对高温金属构件微裂纹的精准检测。本项目所取得的研究成果将为评价上述领域内关键设施中高温、高压服役构件的健康状况提供重要理论支撑与有效技术保障。