核电结构安全和寿命的塑性变形/疲劳损伤一体化电磁无损评价方法研究

Nuclear power plants and other major equipments may be subjected to fatigue load and unexpected loads such as strong earthquakes in the process of service, which will cause fatigue damage and plastic deformation. The plastic deformation may affect the structural safety. The effective evaluation of the plastic deformation and fatigue damage/life of structure as well as the interaction between them is necessary to ensure the structural integrity after earthquakes. The integrated nondestructive evaluation of fatigue damage and plastic deformation is the key technology...Both plastic deformation and fatigue damage will affect the electromagnetic properties of the material. Therefore, the comprehensive analysis of multiple electromagnetic nondestructive testing signals is expected to achieve the integrated evaluation of the two types of damage. ..In order to realize the integrated electromagnetic nondestructive evaluation of structural plastic deformation and fatigue life, the main contents of this project are as follows: 1) To clarify the relationship between the plastic deformation/fatigue damage and the electromagnetic properties of the material and the typical electromagnetic nondestructive testing signals, and also the microscopic mechanism; 2) To develop the integrated quantitative nondestructive evaluation method for plastic deformation and fatigue damage based on eddy current testing/pulsed eddy current tesing, nonlinear eddy current testing signals fusion and inversion problem, and realize the simultaneous assessment of two kinds of damage; 3) To clarify the relationship between the fatigue life and fatigue damage under different plastic deformation, and to establish the integrated nondestructive evaluation method for the nuclear structural safety and lifespan after earthquakes. The research results can be used to evaluate the safety and fatigue life of the structure with plastic deformation, and can be used as an effective means to evaluate the availability of equipment after the extreme load like strong earthquakes.

核电等重大装备服役中会承受起停机和振动/热分层等低高周载荷及可能的强震等意外载荷，导致同时产生疲劳损伤及塑性变形。塑性变形会影响结构安全，确认震后结构完整性必须正确评估塑性变形和疲劳损伤及二者间的相互影响，其中疲劳损伤和塑性变形的一体化无损评价是关键。由于塑性变形和疲劳损伤会从不同侧面影响材料电磁特性，基于多种电磁无损检测信号的综合分析有望实现两种损伤的同步评价。针对上述问题，拟开展研究内容为：1）明确塑性变形和疲劳损伤与核电关键材料电磁特性及典型电磁无损检测信号的关系及微观机理；2）开发基于涡流/脉冲涡流、非线性涡流检测信号融合和反问题的塑性变形/疲劳损伤一体化评价方法，实现损伤的同步定量评估；3）明确不同塑性变形下损伤程度和疲劳寿命的相关性，确立震后核电结构安全和寿命的有效评价技术。研究成果可实现塑性变形结构的安全与疲劳寿命的有效评估，为强震等极端载荷后装备的可用性评价提供有效手段。

核电等重大装备服役中会承受起停机和振动/热分层等低高周载荷及可能的强震等意外载荷，导致同时产生疲劳损伤及塑性变形。塑性变形会影响结构安全，确认震后结构完整性必须正确评估塑性变形和疲劳损伤及二者间的相互影响。核电结构发生的塑性变形多为复杂的双轴塑性变形，要确立震后核电结构安全的有效评价技术，就需要对双轴塑性变形进行无损评估。针对上述问题，本项目开展的研究内容主要分为三个部分，第一部分明确了塑性变形对结构疲劳寿命的影响规律，具体包括：1）测定了SUS304的疲劳寿命曲线，验证了疲劳寿命的经验计算公式；2）建立了塑性变形对SUS304疲劳寿命的影响曲线。第二部分进行了塑性变形和疲劳损伤的无损评价，具体包括：1）设计并制作了单轴塑性变形、疲劳损伤、复合损伤试件和双轴塑性变形试件，通过数值模拟和实验验证了双轴塑性变形试件中央区域塑性变形分布满足应变莫尔圆公式；2）对塑性变形和疲劳损伤进行了脉冲涡流无损评价，验证了脉冲涡流方法对两种损伤进行无损评价的有效性；3）针对双轴塑性变形进行了涡流/脉冲涡流无损评价研究，并通过周向扫描的涡流检出信号建立了双轴应变涡流无损评价的相关公式；4）通过单轴塑性变形对SUS304电导率和相对磁导率影响的标定曲线，建立了双轴塑性变形数值模拟方法并进行了实验验证；5）提出三相品字形旋转涡流探头构型，建立了相应双轴塑性变形检测方法，进行了数值模拟和实验验证，验证了探头和方法的有效性。第三部分研究了塑性变形、疲劳损伤、塑性变形/疲劳复合损伤对材料特性的影响、机理和相互间的联系，具体包括：1）明确了塑性变形、疲劳损伤及其复合损伤对材料特性的影响规律，分析了包括硬度、电导率、马氏体含量、相对磁导率等的材料特性，并探究了塑性变形和疲劳损伤对材料特性影响的联系；2）使用金相显微镜、扫描电镜、原子力/磁力显微镜进行了微观观测，通过晶粒尺寸和微观损伤类型等分析了两种损伤在微观层面上的相互联系，并给出了材料电磁属性变化的微观机理解释。