Abstract
As one of the important non-destructive testing techniques for evaluating material performance degradation and stress state, magnetic Barkhausen noise (MBN) has broad application prospects. Clarifying the relationship between internal stress distribution and detection signal can provide important guidance for evaluating the stress state of material based on the MBN signal. In this work, by constructing the expression of Barkhausen noise excitation intensity related to stress value, combining with the signal attenuation effect during signal propagation, and using the layered model along the thickness direction, we establish the analytical model of MBN signal on the surface of the ferromagnetic plate with internal stress distribution. Based on the existing experimental results, it is confirmed that the proposed model can reflect the effects of the different uniform stresses in the ferromagnetic plate on the signal at different detection frequencies. For the ferromagnetic plate with internal stress distribution, the effects of its stress distribution, magnetic conductivity, electrical resistivity, and thickness on the surface MBN signal are discussed in detail based on the proposed model. The theoretical analysis in this work can be applied to the testing mechanism analysis of the MBN stress evaluation method.
Highlights
magnetic Barkhausen noise (MBN) testing on the ferromagnetic plate under a constant stress
1) (College of Mechanics and Materials, Hohai University, Nanjing, 211100, China) 2) (School of Civil Engineering, Xi’an University of Architecture and Technology, Xi’an 710055, China)
Summary
图 1 铁磁板沿深度方向应力分布诱导的 MBN 信号模型图 Fig. 1. MBN signal model for the stress distribution along the thickness of a ferromagnetic plate. 在实际工程中,经加工强化处理得到的超高强度钢内部常存在残余应力。 服役过程中,残余应力的大小及其分布状态常对结构的安全性能和寿命有很大 影响。本文探讨基于 MBN 信号的板材残余应力检测方法,针对厚度 h (单位为 m)的铁磁板沿厚度方向存在非均匀分布的应力时,建立不同的 Von Mises 等效应 力大小和分布状态下铁磁板表面 MBN 信号的预测模型。图 1 铁磁板沿厚度方向 存在残余应力分布与 MBN 检测示意图,铁磁板由均质且各向同性铁磁材料构成。 建立如图所示坐标系,对矩形铁磁板进行应力检测时,在 y = 0 平面内进行 MBN 信号检测探头的扫查检测。假设探头与铁磁板表面接触良好,MBN 信号. 由探头附近区域的 MBE 与电磁参数等决定,所以 MBN 信号主要受到探头下方 区域随厚度方向变化的应力分布的影响,可忽略与铁磁板表面平行的平面内应 力非均匀分布的影响。. 频率的 MBE。在距检测面 y 处取一微元 ( yi , yi + dy) ,该激发单元产生的 MBE 强 度为Vorig ( y, ) 。由已有文献[19]可知将 MBE 假设为白噪声,因此每个频率对应 的Vorig ( y, ) 具有相同的值。信号传播过程中存在衰减效应,为影响信号传播过. 为由该激发深度所对应的残余应力 唯一决定。对于铁磁板 dy 宽度的微元而言, 可认为微元内部的应力是均匀的,等于激发深度 y 处的等效应力值。式(1)可以 表示为 y. 立 Von Mises 等效应力 在不同取值下的 MBE 强度Vorig ( ) [20]。 基于郎之万理论,非磁滞磁化强度 Man ( H ) 满足[21]. MBN 检测中材料处于弱磁化状态,可对采用式(6)的线性简化形式进行处理 [24],结合式(8)和式(5) 可以得到非磁滞磁化强度 Man ( H , ) 为
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