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，磁体附近厚度方向上的磁通密度分量和后壁附近应力方向上的磁通密度分量之比随板内应变的变化较为敏感。在0~200 mpa的单轴应力下，考察了磁化频率与磁通密度变化的关系。结果表明，200赫兹是提高灵敏度的最合适频率。首先，在空载条件下，磁导率用磁通密度的线性函数来描述。接下来，渗透率被建模为与应变呈线性关系。模型中含有一些未知系数，建立了将实验结果与数值计算结果进行比较来确定未知系数的方法。通过扫描传感器在靠近电磁铁的空间和靠近试件后壁的位置，测量了不同应力值下的磁通密度分布。根据计算结果，给出了传感器对应变的灵敏度分布和传感器定位误差的影响。背面区域适合测量以确定应变。测量了电磁铁升空存在误差时磁通密度的变化。结果表明，误差对电磁铁提离的影响不小。因此，磁体提离的精确设置对于准确地估计应变是很重要的。

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.