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

在本项目中，我们开发了利用激励式高灵敏度磁传感器检测奥氏体不锈钢(SUS304)等结构金属材料疲劳损伤的无损检测系统。为了估算奥氏体不锈钢平板弯曲疲劳损伤量，研究了平面弯曲应力与应力循环次数和差动拾取线圈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取线圈组成。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。结果表明：1)这种新型励磁式磁敏传感器能够很好地捕捉到SUS302奥氏体相变引起的磁导率等电磁性能的变化；其中输出电压的最大值明显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，获得疲劳损伤的净信号，定义了差分输出电压R-R0。4)为了评价疲劳与应力循环次数的关系，在测量区域的中心线上定义了(R-R0)的最大值和最小值的差值。(R-R_0)_&lt；pp&gt；是评定疲劳的有用参数。

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.