Fatigue life of materials or structures can be classified into three stages: fatigue hardening or softening, crack initiation and crack propagation, which includes two stages. Current mature non-destructive testing (NDT) methods can only detect macro or visible cracks in stage II crack propagation. In order to detect and evaluate the fatigue damage occurring before stage II crack propagation quickly and effectively, magneto acoustic emission (MAE) measurement was carried out on laboratory specimens with different numbers of fatigue cycles. With the accumulation of fatigue damage, the RMS of MAE decrease steadily on the whole, making MAE a promising non-destructive method for evaluating fatigue damage. To make MAE applicable in noisy environments, square waveform voltage were selected to excite magnetic fields, and ‘T' type MAE signals with higher amplitude were produced. The variation of MAE with number of fatigue cycles at different excitation intensity indicated that the defects associated with fatigue damage have greater effects on the creation and annihilation of domain walls. The point where the MAE amplitude begins to increase instead of decrease with fatigue can be an indicator for the onset of stage II crack propagation. This article is part of the theme issue ‘Advanced electromagnetic non-destructive evaluation and smart monitoring'.

中文翻译：

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低碳钢疲劳磁声发射特性研究

材料或结构的疲劳寿命可分为疲劳硬化或软化、裂纹萌生和裂纹扩展三个阶段，包括两个阶段。目前成熟的无损检测（NDT）方法只能检测到二级裂纹扩展中的宏观或可见裂纹。为了快速有效地检测和评估在第二阶段裂纹扩展之前发生的疲劳损伤，对具有不同疲劳循环次数的实验室试样进行了磁声发射（MAE）测量。随着疲劳损伤的积累，MAE的均方根值总体上呈稳定下降趋势，使得MAE成为一种很有前景的疲劳损伤无损评估方法。为了使 MAE 适用于嘈杂的环境，选择方波电压来激发磁场，“T” 产生了具有更高幅度的类型 MAE 信号。不同激发强度下 MAE 随疲劳循环次数的变化表明，与疲劳损伤相关的缺陷对畴壁的产生和消灭有更大的影响。MAE 振幅开始增加而不是随着疲劳而减少的点可以作为阶段 II 裂纹扩展开始的指标。本文是主题问题“高级电磁无损评估与智能监测”的一部分。MAE 振幅开始增加而不是随着疲劳而减少的点可以作为阶段 II 裂纹扩展开始的指标。本文是主题问题“高级电磁无损评估与智能监测”的一部分。MAE 振幅开始增加而不是随着疲劳而减少的点可以作为阶段 II 裂纹扩展开始的指标。本文是主题问题“高级电磁无损评估与智能监测”的一部分。