瑞利强散射位错超声协同响应机制及疲劳损伤评价方法

The ultrasonic nondestructive evaluation on the early-stage superficial fatigue damage of coarse-grain austenitic stainless steel is critical for the safety operation of components with high properties such as the pipelines in nuclear power plant and petrochemical industry. Owing to the coarse grain, the austenite shows obvious elastic anisotropy effects on the propagation of ultrasonic wave which is in the regime of strong Rayleigh scattering. How to reveal the response of the damaged medium to ultrasonic wave and extract the ultrasonic features corresponding to the early-stage damage are the bottleneck questions. So in this project, it is proposed to firstly characterize the damage structure, mainly mesoscopic dislocation structure under different cyclic loading stages based electron backscatter diffraction (EBSD) technique. A model will be established with the consideration of the anisotropy of the austenite and the damping resulted from the dislocation structure. Then the nonlinear finite element will be introduced and the A scan signal of critically refracted longitudinal wave will be calculated. In virtue of frequency spectrum and recurrence quantitative analyses, the damage characteristics will be extracted and the relationship will be established between the intrinsic damage index related to crystal orientation and the ultrasonic parameters, including the attenuation coefficient, slope of the attenuation spectrum in frequency domain, and the recursive degree etc. Consequently, the influence of the dislocation accumulation and the grain boundary features on the ultrasonic response physical mechanism could be clarified, and also the collaborative mechanism of the absorbing and scattering attenuations. The results will provide an ultrasonic evaluation method on the superficial fatigue damage of coarse-grain austenitic stainless steel and solution to the development of ultrasonic evaluation theory on the mechanical damage of metallic materials, and support for the engineering examination of components with high properties.

粗晶奥氏体不锈钢早期疲劳损伤无损评价是核电等领域高性能零部件运行安全的迫切需求。粗大奥氏体晶粒呈弹性各向异性，导致超声波传播处于瑞利强散射条件，如何揭示早期损伤声学响应规律、提取损伤对应的声学特征是瓶颈问题。本项目针对粗晶奥氏体不锈钢早期疲劳表面损伤特征，基于高分辨率电子背散射衍射（EBSD）定量表征细观位错结构，建立同时考虑晶粒弹性各向异性和位错阻尼的疲劳损伤声传播模型。研究不同损伤状态位错结构的非线性有限元描述方法，计算一发一收形式下临界折射纵波A扫描信号。利用时、频域处理和递归定量分析提取早期损伤弱信号特征，建立声衰减系数、衰减谱斜率、递归度等声学参量与EBSD局部晶体取向差、花样质量的对应关系，阐明位错累积、晶界特征对弹性各向异性金属损伤声学响应影响规律，揭示超声波吸收衰减和散射衰减的协同机制。发展弹性各向异性粗晶金属早期疲劳表面损伤超声评价理论和方法，支撑高性能零部件工程化检测。

粗晶奥氏体不锈钢早期疲劳损伤无损评价是核电等领域高性能零部件运行安全的迫切需求。粗大奥氏体晶粒呈弹性各向异性，导致超声波传播处于瑞利强散射条件，如何揭示早期损伤声学响应规律、提取损伤对应的声学特征是瓶颈问题。项目针对核电管道用Z2CND18.12N奥氏体不锈钢早期疲劳，从宏观尺度对比分析了面心立方奥氏体循环应力-应变响应，并结合晶体塑性有限元获得了晶粒尺度特征取向的应力-应变演变规律。在细观尺度上，基于EBSD技术定量评价了不同阶段的表面损伤，获得了几何必须位错的细观分布，定量计算了位错类型和位错密度的演变规律。在此基础上发展了基于临界折射纵波的疲劳损伤声学评价方法，结合非线性声学计算阐明了位错、晶界声学响应规律，揭示了超声波吸收衰减和散射衰减的协同机制。提出了基于递归定量分析的损伤信号分析技术与早期损伤弱信号特征的提取方法，实现了奥氏体不锈钢早期疲劳表面损伤的超声无损评价，为相关高性能金属零部件工程化检测与评价提供有力支撑。.项目发表学术论文8篇，其中SCI检索3篇，EI刊源期刊论文3篇；申请中国发明专利4项、国际发明专利1项，已授权1项，软件著作权1项。1项专利和1项软件著作权实现技术转让，取得显著效果。参加国内外学术会议各1次。受国际焊接学会邀请，作为唯一中国学者参加国际团队开展为期三年的权威手册修订工作。所指导的博士生获得“奥林巴斯杯2021超声检测技术论文评选”优秀论文三等奖。