Abstract Non-destructive testing techniques are widely applied in industry for the evaluation of quantities of interest without inflicting additional damage accumulation. Crack detection and monitoring is a prime example of where non-destructive testing is valuable. Among the variety of non-destructive testing techniques, the direct current and alternating current potential difference methods, which are based on the principle that an electrical potential field around a conductive specimen is disturbed by the presence of geometric irregularities (or “features”), have received a great deal of attention in the literature. This is mainly due to the high levels of accuracy associated with these techniques and good estimations of crack initiation and propagation having been achieved. A critical review of the evolution and applications of potential difference methods is presented in this paper. Potential difference methods are capable of providing accurate and continuous measurements with simple installation and exclude the requirement of visual access under harsh service conditions. Alternating current potential difference methods require lower current input than direct current equivalents and hence provide higher sensitivity and offer better noise rejection but are vulnerable to capacitance effects and are more expensive. Calibration curves can be determined analytically, numerically, or by direct or analogue experimental techniques with each method offering strengths and limitations. Application of these should be determined in accordance with the specific scenario. The performance of electric probes (of voltage measurements and current injection) on top- and side-face of C(T) and SEN(B) specimens are reviewed in detail as case examples. Specific guidance in normalising measurements and eliminating errors from thermoelectric effects can be implemented in order to improve the accuracy of PD methods. Abundant results have been obtained by applying PD methods in monitoring cracks geometries under aggressive conditions such as corrosion, high temperature, creep and cycled loading.

中文翻译：

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测量裂纹增长的潜在差异方法：综述

摘要 无损检测技术在工业中被广泛应用于评估感兴趣的数量，而不会造成额外的损伤累积。裂纹检测和监测是无损检测价值的一个主要例子。在各种无损检测技术中，直流电势差法和交流电势差法基于导电样品周围的电势场受到几何不规则（或“特征”）的存在干扰的原理，受到文学界的广泛关注。这主要是由于与这些技术相关的高精度和已实现的裂纹萌生和扩展的良好估计。本文对电位差方法的演变和应用进行了批判性回顾。电位差法能够通过简单的安装提供准确和连续的测量，并且在恶劣的服务条件下排除了目视访问的要求。交流电势差方法需要比直流等价物更低的电流输入，因此提供更高的灵敏度和更好的噪声抑制，但容易受到电容效应的影响并且更昂贵。校准曲线可以通过分析、数值或直接或模拟实验技术来确定，每种方法都有其优势和局限性。这些的应用要根据具体的场景来确定。作为案例详细审查了 C(T) 和 SEN(B) 样品顶面和侧面的电探针（电压测量和电流注入）的性能。可以实施标准化测量和消除热电效应误差的具体指导，以提高 PD 方法的准确性。通过在腐蚀、高温、蠕变和循环载荷等侵蚀性条件下应用 PD 方法监测裂纹几何形状，已经获得了大量结果。