基于非线性超声检测的离心压缩机叶轮超高周疲劳损伤评价和寿命估算方法研究

Very high cycle fatigue is one of the important forms of centrifugal compressor impeller failure, and its early damage accounts for the majority of very high cycle fatigue life. The nonlinear ultrasonic testing can effectively characterize the degradation of internal mechanical properties and the degree of micro-defect damage in the early stage of fatigue, and can be used for the evaluation of early fatigue damage of centrifugal compressor impeller. This project uses theoretical analysis, very high cycle fatigue test, nonlinear ultrasonic test and finite element numerical simulation to study the nonlinear ultrasonic evaluation method for very high cycle fatigue damage of centrifugal compressor impeller. The main contents include: studying the nonlinear parameter characterization of very high cycle fatigue micro-damage of impeller, clarifying the influence of micro-defects such as dislocation pile-up, micro-hole and micro-crack on the nonlinear parameter, revealing the mechanism of the change of nonlinear parameter caused by the microstructure of very high cycle fatigue damage, and establishing the "equivalent crack" size calculation model which can effectively reflect the micro-fatigue damage. Furthermore, the very high cycle fatigue damage evaluation and fatigue life estimation method of centrifugal compressor impeller based on nonlinear ultrasonic testing are proposed, which provides theoretical support and experimental basis for safety service and the in-service detection of centrifugal compressor impeller early fatigue damage. This project has important theoretical, engineering and social implications.

超高周疲劳是离心压缩机叶轮失效的重要形式之一，其早期损伤占据了超高周疲劳寿命的绝大部分。非线性超声检测技术能够有效表征材料疲劳早期内部力学性能退化和微缺陷损伤程度，可用于离心压缩机叶轮早期疲劳损伤的评价。本项目采用理论分析、超高周疲劳试验、非线性超声检测试验 和有限元数值模拟等方法，研究了离心压缩机叶轮超高周疲劳损伤的非线性超声评价方法，主要内容包括：研究叶轮超高周疲劳微观损伤的非线性参量表征，明确位错塞积、微孔洞、微裂纹等微观缺陷对非线性系数的影响规律，揭示超高周疲劳损伤早期的微观结构导致非线性系数变化的作用机理，建立能够有效反映微观疲劳损伤的“当量裂纹”尺寸计算模型，进而提出基于非线性超声检测的离心压缩机叶轮超高周疲劳损伤评价和寿命估算方法，为离心压缩机叶轮安全服役和早期疲劳损伤的在役检测提供理论支持和实验依据，具有重要的理论、工程和社会意义。

离心压缩机叶片工作转速高、服役时间长、工况条件恶劣，其失效形式以叶片的疲劳损伤为主，材料内部的隐性损伤占据了早期损伤的很大一部分。非线性超声检测技术能够有效表征材料疲劳早期内部力学性能退化和微缺陷损伤程度，可用于叶片材料疲劳损伤的评价。本项目针对离心压缩机叶片材料FV520B钢开展了疲劳损伤的非线性超声表征和评价方法研究，具体研究进展如下：1、获得了叶片材料FV520B拉伸塑性应变和超声非线性参量间的映射关系以及全寿命周期不同疲劳损伤程度下归一化超声非线性参量与疲劳循环周次间的映射关系，实现了叶片材料FV520B塑性损伤和疲劳损伤的非线性参量表征；2、研究了材料内部微裂纹、微孔洞等早期损伤的尺寸、密度、分布等多种因素对超声非线性参量的影响规律，建立了塑性应变损伤因子和应力强度因子的超声非线性参量等效方法，揭示了叶片材料FV520B疲劳微观损伤诱发声学非线性响应的机理。3、建立了反映材料早期损伤程度的“等效裂纹尺寸”方法，实现了叶片材料FV520B疲劳寿命的定量估算（β-a-N），提出了基于非线性超声检测的疲劳损伤程度和剩余寿命估算方法。