Research on Evaluation of Strain-Permeability Relationship for Strain Measurement

1. 测量了放置在铁磁板上的电磁铁附近的磁通密度。结果表明，磁通密度的两个分量，即磁铁附近的厚度方向分量和后壁附近的应力方向分量的比值，随着板内应变的变化而敏感地变化。在0 ~ 200MPa的单轴应力下，研究了磁感应强度与磁化频率的变化关系。结果表明，灵敏度最适宜的频率为200hz。首先，将磁导率建立为空载条件下磁通密度的线性函数模型。其次，建立了渗透率与应变的线性关系模型。模型中存在一些未知系数，建立了通过对比实验结果与数值结果确定未知系数的方法。通过扫描传感器在靠近电磁铁和试样后壁附近的空间，测量不同应力值下的磁通密度分布。结果表明了应变灵敏度的分布规律和误差对传感器定位的影响。背面区域适合测量以确定应变。测量了电磁体在发射过程中存在误差时的磁通密度变化。结果表明，电磁铁升空误差的影响是不小的。因此，磁体升降的精确设置对于准确地评估应变是非常重要的。

1. The magnetic flux density was measured near the electromagnet put on the ferromagnetic plate. It was shown that the ratio of two components of the magnetic flux density, which are the component in the thickness direction near a magnet and the one in the stress direction near a back-wall, changes sensitively with the change in strain in the plate.2. The relation of the change in magnetic flux density and frequency used for magnetization was examined under uniaxial stress of 0 to 200MPa. It was shown that the most suitable frequency for sensitivity is 200 Hz.3. First, the permeability was modeled by a linear function of the magnetic flux density under a no load condition. Next, the permeability was modeled to relate with the strain in a linear form. The model contains some unknown coefficients, The method to determine the coefficients by comparing experimental results with numerical those using the model was established.4. By scanning the sensor in the space near the electromagnet and near the back-wall of the specimen, the distribution of magnetic flux density was measured for various values of stress. From the results, the distribution of sensitivity for strain and influence of error in sensor positioning were shown. The back side area is suitable for the measurement to determine strain.5. The change in magnetic flux density was measured when lift-off of an electromagnet contained error. From the results, it was shown that the influence of error in lift-off of the electromagnet is not small. Then the precise setting of lift-off of the magnet is important for accurate evaluation of strain.