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，我们利用FG磁传感器对奥氏体不锈钢的疲劳损伤进行了评估，并开发了利用激励型高灵敏度磁传感器检测金属材料疲劳损伤的无损评估系统。为了评估奥氏体不锈钢板材的弯曲疲劳损伤量，我们研究了奥氏体不锈钢板材马氏体组织引起的平面弯曲应力与残余磁化强度之间的关系。利用高灵敏度薄膜磁通门磁传感器测量了样品上方1 mm处残余磁化引起的Z分量的磁通密度。涡流探头是一种新型的奥氏体不锈钢疲劳损伤磁传感器，由一个励磁线圈和两个缠绕在铁氧体铁芯上的拾取线圈组成。结果表明：1)随着弯曲应力(σ_a)的增大，B&lt；Zmax&gt；值明显增大；3)利用FG磁敏传感器可以检测到SUS304、SUS304L、SUS316和SUS316L等试件上因残余磁化而产生的微小漏磁场密度。4)SUS316系列的残余磁化强度比SUS304系列的小约十倍。5)这种新型的涡流探头能够很好地捕捉到SUS304中奥氏体向马氏体转变引起的磁导率等电磁性能的变化。

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.