叶片复杂型面的柔性超声相控阵检测原理与技术基础研究

The aero-engine operates at extreme environment such as elevated temperature, high corrosion and high loading, So the defects will probably occur during its service life, which leads to serious accidents. It is the fundamental and support for the service performance guarantee of key materials in aerospace and other fields to research on in-situ nondestructive testing technology for the inspection of micro defects in the complex curved components such as turbine blades. However, this research work strongly depends on the breakthrough of the advanced testing technologies and instruments. So, we propose a new key technology of flexible phased array ultrasonic testing (FPAUT) for the inspection of complex curved components in this project. The research works include the basic theories, such as the delay law of flexible phased array for variable curvature, the analytical model of acoustic pressure distribution of flexible arrays, the FEM model for micro defect response inside the curved structures, and the micro-defect high-precision imaging algorithm of FPAUT. Then, the stable and reliable flexible transducers and test system of FPAUT will be developed. We are striving to solve the key scientific problems, such as the theories of acoustic field of flexible arrays for the inspection of complex curved components, and the fundamental law of generation and propagation of ultrasonic phased array waves response to micro defects. Then, the failure mechanisms and evolution laws of micro damages inside turbine blade will be obtained. The research results provide the core technical support for advanced material research and development, forming and manufacturing, service performance evaluation of complex curved components of high-end equipment in aerospace field, which is of great scientific significance and will bring significant social and economic benefits.

航空发动机长期工作在高温、高腐蚀、高载荷等极端工况中，在服役过程中易产生损伤缺陷，致使重大事故频出。涡轮叶片等复杂型面构件内部微小缺陷的原位无损检测研究，是航空航天等众多领域关键材料服役性能保障的重要基础与支撑，但该研究强烈依赖于先进检测技术和仪器的突破。本项目提出叶片复杂型面构件的柔性超声相控阵无损检测理论与技术，攻克变曲率曲面相控阵延时准则、变曲率曲面相控阵换能器声场模型、复杂型面构件中损伤缺陷响应的相控阵超声有限元模型、微小缺陷高精度成像算法等基础理论，研制性能稳定可靠的柔性换能器和检测系统。力图解决变曲率复杂型面构件的换能器声场理论以及微小缺陷响应的超声相控阵的激励与传播规律的关键科学问题，获取涡轮叶片失效机制及其缺陷演化规律。研究成果将为航空航天等高端装备复杂型面构件的新材料研发、成形制造以及服役性能评估等提供核心技术支撑，具有重要科学意义，将产生重大的社会和经济效益。

为攻克复杂曲面构件缺陷检测难题，打破现有柔性相控阵技术应用的局限性，本项目推导了复杂曲面构件的柔性相控阵时间延迟法则，并以此为基础建立柔性超声相控阵检测声场分布解析模型、偏转聚焦声波传播及缺陷散射数值仿真模型。基于理论与仿真，搭建了超声相控阵自动化检测平台，开展柔性相控阵探头的实际应用研究。.建立了单层凹面、凸面、凹/凸面的一维柔性阵列及单层凹面、凸面工件检测的二维柔性阵列时间延迟法则。进一步根据斯涅尔定律与费马原理，建立双层凹面、凸面工件的声线传播几何模型，推导了精确的时间延迟法则。推导单阵元归一化声压幅值表达式，结合各阵元时延规律，得到了整个柔性阵列检测单层与双层复杂曲面构件的声场分布模型。为验证解析模型的正确性，模拟了凹面、凸面、凹/凸面试件有、无时间延迟的声场分布情况。并提取声场分布图轴向声压曲线来定性分析曲面半径、偏转角及聚焦长度对声束聚焦特性的影响规律。为优化设计柔性阵列探头及检测方案，探究了阵列孔径、阵元中心距、阵元宽度、探头频率及偏转角对声束特性的影响规律。在时间延迟聚焦法则的基础上，建立了复杂曲面试件内声波传播及缺陷检测的声场时域仿真模型，合成声波能按照预设方向传播并在指定位置聚焦。利用时间延迟法则使各阵元回波信号相位一致，再对其叠加，可获得声压幅值大大增强的回波信号，用于缺陷的定位、定量分析。且利用缺陷检测仿真数据揭示了阵列孔径、聚焦长度及声束偏转角对检测结果的影响规律。搭建了柔性相控阵检测平台，并对凹面、凸面、凹/凸面工件内多个孔缺陷进行检测，缺陷检测B扫描视图与缺陷实际位置一致。且通过缺陷检测试验A扫描信号与有限元回波数据的一致性，验证了有限元缺陷检测仿真模型的正确性和可行性。而且开展了涡轮叶片不同类型、不同尺寸的缺陷检测试验，结果表明利用所推导的时间延迟法则及检测声场模型，柔性相控阵探头能对复杂曲面试件内的微小缺陷进行精确评估与表征。