调幅切向磁场对低碳钢残余塑性应变的检测灵敏度矩阵分析方法

Sensitivity matrix analysis for residual plastic strain evaluation method using amplitude modulation tangential magnetic field in low carbon steel

针对低碳钢的残余塑性应变定量评估问题,提出了一种基于调幅切向磁场测量的无损检测新方法:采用U型电磁铁提供调幅磁场对低碳钢试件进行磁化,单一霍尔元件检测表面切向磁场,其输出电压随线性调幅激励电压变化而形成的蝶形轨迹可用于残余塑性应变表征。研究发现在蝶形轨迹的大部分区域,霍尔元件输出电压与低碳钢中静态拉伸形成的残余塑性应变的平方根间存在良好的线性关系。为实现残余塑性变形的最佳灵敏度表征,将蝶形轨迹进行矩阵化并计算得到检测灵敏度矩阵,分析了不同励磁条件下霍尔元件输出电压对残余塑性应变平方根的灵敏度,结果显示:在弱磁化条件(励磁周期的峰值电压与线性调幅电压最大峰值的百分比为15%)下,霍尔元件输出电压对残余塑性应变平方根的检测灵敏度最高。新方法实施简便,结合检测灵敏矩阵,可对励磁条件和敏感区域进行优化选取,有望推广运用于其他力学性能指标的高灵敏度无损检测。

A new non-destructive method is proposed for residual plastic strain evaluation in low- carbon steel based on amplitude-modulated tangential magnetic field measurement technique. A U- shape electromagnet is employed to provide an amplitude-modulated magnetic field for low carbon steel specimen magnetization. A single Hall element is used to measure the tangential magnetic field near the specimen surface. The butterfly trajectory representing the dependency of output voltage of Hall element on the amplitude-modulated excitation voltage can be used for residual plastic strain characterization. It is found that in most region of the butterfly trajectory there is a good linear relationship between the output voltage of Hall element and the square root of the residual plastic strain formed by static stretching in low carbon steel. To achieve characterization of square root of the residual plastic strain by using output voltage of Hall element with highest sensitivity, the butterfly trajectory is transferred into matrix, and the sensitivity matrix is derived accordingly. The dependency of the sensitivity on the magnetization state of the material is investigated to show that when the material is in its weak magnetization state (the percentage between the peak voltage of excitation period and the maximum peak of linear amplitude modulation voltage is 15%), the parameter of output voltage of Hall element possesses highest sensitivity to the value of the square root of the residual plastic strain. The implementation of the new method is very convenient, and the sensitivity matrix is helpful for the optimization of the excitation magnetic field and the selection of the sensitive region in the matrix. It is expected that the new method is able to nondestructively evaluate other mechanical properties with high sensitivity.