While fatigue crack growth can be measured by the standard unloading compliance method, it requires a proper COD gauge and may not be applicable in harsh conditions, such as high temperature or corrosive environments. On the other hand, modern fatigue test machines have an accurate built-in sensor to measure the stroke position, representing the total system deflection within the load train. In this paper, an innovative method is proposed to determine specimen compliance accurately from the total system deflection data. This method can be used to measure the fatigue crack growth of standard specimens without a COD gauge or any other reference specimen. Each individual test specimen serves as a reference for determining the in-situ machine compliance. Therefore, the only prerequisite is exact information on the initial crack length and the elastic modulus of the specimen. Test results from three different materials demonstrated that the method works very successfully for fatigue crack growth tests under constant or decreasing peak load conditions. The methodology was successfully implemented in the development of an automatic pre-cracker for fracture mechanics specimens. Additionally, fatigue crack growth tests at high temperature were successfully conducted under normal test room conditions.

中文翻译：

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无需 COD 测量仪即可测量疲劳裂纹扩展的创新方法

虽然疲劳裂纹扩展可以通过标准卸载合规方法进行测量，但它需要合适的 COD 测量仪，并且可能不适用于恶劣条件，例如高温或腐蚀环境。另一方面，现代疲劳试验机具有精确的内置传感器来测量行程位置，代表负载链内的总系统偏转。在本文中，提出了一种创新方法，可以根据整个系统挠度数据准确确定样本柔度。该方法可用于测量标准样品的疲劳裂纹扩展，无需 COD 测量仪或任何其他参考样品。每个单独的测试样本均可作为确定现场机器合规性的参考。因此，唯一的先决条件是关于初始裂纹长度和样本弹性模量的准确信息。三种不同材料的测试结果表明，该方法在恒定或减少的峰值载荷条件下非常成功地进行疲劳裂纹扩展测试。该方法已成功应用于断裂力学试样自动预破碎机的开发中。此外，在正常试验室条件下成功进行了高温疲劳裂纹扩展试验。