AC magnetic flux leakage (ACMFL) testing is a novel method for the detection of defects of metallic materials. Conventional ACMFL probes excited by a single-frequency (SF) sine signal have limitations in accurately detecting the defect size and identifying the defect orientation. In this article, a multifrequency ACMFL (MF-ACMFL) method is proposed to address these issues. First, we give a thorough analysis of the effects of excitation frequencies on magnetic flux density under different defect sizes and orientations using the finite-element method. The numerical results indicate that the optimal frequencies are 400 and 500 Hz to detect the defect size, and that to identify the defect orientation are approximately 400–500 Hz. Then, we compare the receiver signal under SF and MF excitations and estimate the size of the defect including its length, width, and depth under oblique angles of 0° and 30°, whose results validate the effectiveness of the proposed method. Finally, measuring the depths and orientations of the defect on the thick steel plate verifies the correctness of the numerical results and the advantage of the proposed method in the orientation identification of the defect. Thus, the proposed scheme is an effective complementary measure for the existing ACMFL tools.

中文翻译：

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用于检测厚钢板缺陷尺寸和方向的交流漏磁测试的最佳频率

交流漏磁 (ACMFL) 测试是一种检测金属材料缺陷的新方法。由单频 (SF) 正弦信号激发的传统 ACMFL 探针在准确检测缺陷尺寸和识别缺陷方向方面存在局限性。在本文中，提出了一种多频 ACMFL (MF-ACMFL) 方法来解决这些问题。首先，我们使用有限元方法全面分析了不同缺陷尺寸和取向下激励频率对磁通密度的影响。数值结果表明，检测缺陷尺寸的最佳频率为 400 和 500 Hz，识别缺陷方向的最佳频率约为 400-500 Hz。然后，我们比较 SF 和 MF 激励下的接收器信号并估计缺陷的大小，包括其长度，0°和30°斜角下的宽度和深度，其结果验证了所提出方法的有效性。最后，通过对厚钢板缺陷深度和取向的测量，验证了数值结果的正确性和所提方法在缺陷取向识别中的优势。因此，所提出的方案是对现有 ACMFL 工具的有效补充措施。