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

在本项目中，我们开发了利用混合磁传感器对厚金属板背面的天然裂纹进行无损检测的系统。混合式磁敏传感器由重力磁敏传感器和励磁系统组成。这种采用MI元件的新型混合式磁传感器具有很高的灵敏度和稳定性。另一方面，为了估算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。用高灵敏度的薄膜磁通门磁敏传感器测量了样品上方1 mm处剩余磁化引起的Z分量的磁通密度。它可以检测到非常小的磁通密度。根据我们的实验，在试件上方1 mm处由剩余磁化引起的磁通密度与弯曲st…的增加有明显的依赖关系。压力越大，压力循环的次数越多。本项目的研究成果如下：1)由叠层硅钢板制成的U形激磁磁芯的混合型磁传感器可以清晰地检测到5 mm厚钢板上1 mm深、5 mm长、0.5 mm宽的反面缺陷。2)由铁氧体制成的U形激磁磁芯的混合型磁传感器可以清楚地检测到5 mm厚不锈钢板上1 mm深的反面缺陷。3)随着弯曲应力和应力循环次数的增加，磁通密度的Z分量(δB_z)的变化明显增加。δB_z的值取决于弯曲应力。4)δBz的值(=B_&lt；Zmax&gt；-B_&lt；Zmin&gt；)。5)奥氏体不锈钢板材的残余磁化强度取决于弯曲疲劳损伤的大小。6)如果弯曲应力小于疲劳极限，则循环弯曲应力会逐渐诱导奥氏体不锈钢板材中的马氏体组织。7)即使在1.0×10~(-7)次的弯曲循环中，也会诱发马氏体相变，低于疲劳极限。较少

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