Development of Nondestructive Evaluation System Using the Excitation Type High Sensitivity Magnetic Sensor to Ddetect Fatigue Damage of Metallic Material

在本项目中，我们阐明了使用FG磁传感器评估奥氏体不锈钢疲劳损伤的以下结果，并开发了使用励磁型高灵敏度磁传感器检测金属材料疲劳损伤的非破坏性评估系统。为了评估奥氏体不锈钢板的弯曲疲劳损伤量，研究了奥氏体不锈钢板中马氏体组织引起的平面弯曲应力与剩余磁化强度的关系。采用高灵敏度的薄膜磁通门磁传感器测量了试样上方1 mm处的Z分量剩余磁化引起的磁通密度，涡流探头是一种用于检测奥氏体不锈钢疲劳损伤的新型磁传感器，它由一个励磁线圈和两个绕在铁氧体磁芯上的拾波线圈组成。结果表明：1）B_值<zmax>随弯曲应力（σ_a）和N的增大而明显增大; 2）B_值<zmax>是估算疲劳损伤量的一个有用参数; 3）在SUS 304、SUS 304 L、SUS 306 L、SUS 306 L等试件上，可以检测到微小的漏磁密度，SUS 316系列和SUS 316L系列使用FG磁性传感器产生的剩磁。4）SUS 316系列的剩磁比SUS 304系列小约10倍。5）这种新的涡流探头确实能够捕捉到SUS 304中奥氏体向马氏体转变所引起的电磁性能（如磁导率）的变化。6）Rc_的值<max>明显取决于应力循环次数。

In this project, we have elucidated the following results for the evaluation of fatigue damage in an austenitic stainless steel using the FG magnetic sensor and we developed the non-destructive evaluation system using the excitation type high sensitivity magnetic sensor to detect fatigue damage of metallic material.In order to estimate the amount of bending fatigue damage on austenitic stainless steel plates, we have investigated the relationship between plane bending stress and residual magnetization caused by martensitic structure in austenitic stainless steel plates. Magnetic flux density in the Z component caused by residual magnetization at 1 mm above a specimen is measured by using a high sensitivity thin-film flux-gate magnetic sensor.The eddy current probe which is a new magnetic sensor to detect fatigue damage on austenitic stainless steels consists of an excitation coil and two pick-up coils wound on a ferrite core. The size of the EC probe is 10 mm x 4 mm x 8 mm.Results of this project are shown as follows:1) The value of B_<zmax> clearly increases with the increase of the bending stress (σ_a) and N.2) The value of B_<zmax> is a useful parameter to estimate the amount of fatigue damage.3) We could detect the small leakage magnetic flux density on the specimens such as SUS304, SUS304L, SUS316 and SUS316L caused by the residual magnetization by using the FG magnetic sensor.4) The residual magnetization in SUS316 series is about ten times smaller than SUS304 series.5) This new eddy current probe was surely able to catch the change in electromagnetic properties such as magnetic permeability caused by the transformation from austenite to martensite in SUS304.6) The value of Rc_<max> obviously depends on the number of stress cycles.