Development of Non-destructive Evaluation System Using the Hybrid Magnetic Sensor for Natural Cracks on a Reverse-side of thick metallic Plates

在这个项目中，我们开发了一种使用混合磁传感器的非破坏性评估系统，用于厚金属板背面的自然裂纹。混合式磁传感器由磁传感器和励磁系统组成。这种新型混合磁传感器采用MI元件，具有较高的灵敏度和稳定性。另一方面，为了估计奥氏体不锈钢板的弯曲疲劳损伤量，我们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残余磁化强度的关系。采用高灵敏度薄膜磁通门磁传感器测量试样上方1mm处残余磁化引起的Z分量的磁通密度。它可以探测到非常小的磁通密度。实验结果表明，残余磁化引起的试样上方1mm处的磁通密度与弯曲强度、应力和应力循环次数的增加有明显的关系。本课题的研究结果如下：1)复合硅钢片u型激励磁芯混合磁传感器在5mm厚的钢板上清晰地检测到1 mm深、5 mm长、0.5 mm宽的反面缺陷。2)铁氧体u型励磁磁芯混合磁传感器可以在5mm厚的不锈钢板上清晰地检测到1 mm深的背面缺陷。3)磁通密度Z分量的变化（δB_z）随弯曲应力和应力循环次数的增加而明显增大。δB_z的值取决于弯曲应力。4) δBz的值（=B_<zmax>-B_<zmin>）。显然取决于弯曲应力。5)奥氏体不锈钢板的残余磁化强度取决于弯曲疲劳损伤的程度。6)当弯曲应力小于疲劳极限时，循环弯曲应力逐渐诱发奥氏体不锈钢板中的马氏体组织。7)在小于疲劳极限的1.0 × 10^7次弯曲下，马氏体也发生转变。少

In this project, we developed the non-destructive evaluation system used the hybrid magnetic sensor for natural cracks on a reverse-side of thick metallic plates. The hybrid magnetic sensor consists of a gradio-magneto sensor and an exciting system. This new hybrid magnetic sensor using MI elements shows high sensitivity and stability. On the other hand, 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. It can detect a very small magnetic flux density. From our experiments, the magnetic flux density at 1 mm above a specimen caused by residual magnetization has clear dependences on the increase of bending st … More ress and the number of stress cycles. Results of this project are shown as follows :1) The hybrid magnetic sensor with a U-shaped exciting core made of laminated silicon steel plate clearly detect a 1 mm depth, 5 mm length, 0.5 mm width reverse-side defect on a 5 mm thick steel plate.2) The hybrid magnetic sensor with a U-shaped exciting core made of ferrite can clearly detect a 1 mm depth reverse-side defect on a 5 mm thick stainless steel plate.3) The change of the Z component of the magnetic flux density (δB_z) clearly increases with increase in the bending stress and the number of stress cycles. The value of δB_z depends on the bending stress.4) The value of δBz (=B_<zmax>-B_<zmin>). obviously depends on the bending stress.5) The residual magnetization in austenitic stainless steel plates depends on the amount of the bending fatigue damage.6) If the bending stress is less than the fatigue limit, martensitic structure in austenitic stainless steel plates is gradually induced by the cyclic bending stress.7) Martensite transformation is induced even over 1.0x10^7 cycles of bending, less than the fatigue limit. Less