ABSTRACT

Since magnetic Barkhausen noise is very sensitive to the change of the stress or residual stress level in components, it is feasible to detect the stress or residual stress profile along the depth direction by the magnetic Barkhausen noise method. An engineering approach was used to validate a theoretical model describing the relationship between magnetic Barkhausen noise and stress magnitude. To generate stress gradients in the specimen of Q235 steel under different deflections, the four-point bending device was used. Then the detected signals obtained in the experiment were divided into different sub-bands to evaluate the stress at different depths. The testing depth was set to be around 100 μm due to the rapid exponential attenuation of the noise signals. In the experiments, the sub-band energy density showed sensitive as the loading displacement increasing. The experimental results showed that the signal energy was also sensitive to the plastic deformation of the material. Within the depth of 100 μm, the stress change was very small. The final experimental results showed that even under such small stress variations, it is sensitive and feasible to use the magnetic Barkhausen noise energy to characterise the change of stress gradients.

摘要

由于磁巴克豪森噪声对构件内应力或残余应力水平的变化非常敏感，因此采用磁巴克豪森噪声法检测沿深度方向的应力或残余应力分布是可行的。使用工程方法来验证描述磁性巴克豪森噪声与应力大小之间关系的理论模型。为了在 Q235 钢试样中产生不同挠度下的应力梯度，使用了四点弯曲装置。然后将实验中得到的检测信号划分为不同的子带，以评估不同深度的应力。由于噪声信号的快速指数衰减，测试深度设置为 100 μm 左右。在实验中，随着加载位移的增加，子带能量密度表现出敏感。实验结果表明，信号能量对材料的塑性变形也很敏感。在 100 μm 深度内，应力变化非常小。最终的实验结果表明，即使在如此小的应力变化下，利用磁巴克豪森噪声能量来表征应力梯度的变化也是灵敏可行的。