基于自然磁化现象的损伤定量无损检测方法

摘要

为了开发对材料裂纹产生前的早期损伤程度进行定量无损检测的新方法,探讨自然磁化机理,以核能设备中常用的常磁性材料--奥氏体不锈钢SUS304为研究对象,通过实验对不同形状和厚度的材料试样进行多次拉伸,测量相应的自然磁化漏磁场磁感应强度和残余应变分布,从而建立了基于自然磁化现象的机械损伤与其磁化漏磁场的定量关系,进而证明了可以通过检测自然磁化漏磁场强度实现对奥氏体不锈钢材料损伤程度的定量检测和评估.基于实验所建立的机械损伤与自然磁化漏磁场的定量关系,结合磁记忆检测方法的优点,提出了一种较为简单但更为全面的对局部缺陷损伤程度进行定量检测的方法.奥氏体不锈钢的自然磁化机理可以初步认为是机械损伤引起的位错堆积导致了奥氏体不锈钢中马氏体含量和位错能的增加,由于材料的各向异性致使在铁磁属性的马氏体组织内产生了自然磁化,从而使材料整体呈现自然磁化特性.%To develop a new nondestructive testing (NDT) method for nondestructive evaluation of mechanical damage before the initiation of macro cracks and reveal the mechanism of natural magnetization, the quantitative correlation between the natural magnetization and the mechanical damage was experimentally investigated for a typical austenitic stainless steel SUS304, which is extensively used in nuclear power plants. In the experiments, simple tensile loading was performed to initialize plastic damages in specimens under different states. The corresponding leakage magnetic field due to natural magnetization and the residual strain distribution were measured after each loading cycle. The quantitative relation between mechanical damage and leakage magnetic field was established based on the phenomenon of natural magnetization, which shows the possibility to quantitatively detect mechanical damages in the austenitic stainless steel by measuring the natural magnetic field. Following the above results and combining with the advantages of metal memory measurement, a new mechanical damage detection method via NDT is presented.