Development of Fatigue Evaluation System for Structural Metallic Material Using the Eddy Current Type High Sensitivity Magnetic Sensor

在本项目中，我们开发了使用激励型高灵敏度磁传感器的非破坏性评估系统，以检测奥氏体不锈钢（SUS 304）等结构金属材料的疲劳损伤。为了估算奥氏体不锈钢板的平面弯曲疲劳损伤量，我们研究了平面弯曲应力与应力循环次数和新型励磁型磁传感器的差动拾波线圈的输出电压之间的关系。励磁式磁传感器由一个励磁线圈和两个拾波线圈组成。EC探头的尺寸为10 mm x 4 mm x 8 mm。这些线圈围绕铁氧体磁芯形成。实验结果表明：1）这种新型励磁式磁传感器能够准确地捕捉到SUS 304钢中奥氏体向马氏体转变所引起的磁导率等电磁特性的变化; 2）其<cmax>输出电压的最大值R_（？）明显地取决于应力循环次数和平面弯曲应力; 3）为了消除圆缺口噪声信号的影响，定义输出电压差R-R_0，以获得疲劳损伤的净信号; 4）在测量区域中心线定义（R-R_0）的最大值与最小值之差，以评价疲劳与应力循环次数的关系。（R-R_0）_的值<pp>是评价疲劳的有用参数。

In this project, we developed the non-destructive evaluation system using the excitation type high sensitivity magnetic sensor to detect fatigue damage of structural metallic material such as austenitic stainless steels (SUS304). And we have elucidated the following results for the evaluation of fatigue damage in SUS304 using the Excitation type magnetic sensor.In order to estimate the amount of plane bending fatigue damage on austenitic stainless steel plates, we have investigated the relationship among plane bending stress and the number of stress cycles and the output voltage of the differential pick-up coil of the new excitation type magnetic sensor. The excitation type magnetic sensor consists of an excitation coil and two pick-up coils. The size of the EC probe is 10 mm x 4 mm x 8 mm. These coils are formed around the ferrite core. Two pick-up coils are connected differentially.Results of this project are shown as follows:1) This new excitation type magnetic sensor was surely able to catch the change in electromagnetic properties such as magnetic permeability caused by the transformation from austenite to marten site in SUS304.2) The value of R_<cmax> which is the maximum value of the output voltage from it obviously depends on the number of stress cycles and plane bending stress.3) In order to eliminate the influence of the noise signal from round notches, and to obtain net signal from fatigue damage, the differential output voltage R-R_0 was defined.4) To evaluate the relationship between fatigue and the number of stress cycles, difference between the maximum value and the minimum value of (R-R_0) was defined in the center line in the measurement area. The value of (R-R_0)_<pp> is a useful parameter to evaluate fatigue.