For critical engine parts, such as crankshafts, fatigue strength is one of the most important parameters in the design and manufacturing stage. In previous work, fatigue limit loads of the crankshafts with different structural features were predicted based on different theories of critical distance (TCDs). The results showed that the definition of the TCD had an obvious impact on the accuracy of such predictions. This paper, first the critical distance was determined based on the limit stress distribution of a given crankshaft and the definition of the approach. Then, the fatigue limit load of another crankshaft was predicted based on the parameters obtained in the previous step. Finally, corresponding experimental verification and model parameter error influence analysis were conducted to evaluate the accuracies of the predictions. The results showed that for the modified indirect-defined TCD (ITCD), the predictions based on the line and point methods were approximately equal, and the parameter errors had an obvious impact on the predictions. However, for the direct-defined TCD (DTCD), the critical line approach had much better accuracy than the critical point approach, and the DTCD was much less sensitive to the model parameter errors than the ITCD approach, therefore, the DTCD approach is much more suitable for actual engineering applications.

对于关键的发动机零件（例如曲轴），疲劳强度是设计和制造阶段中最重要的参数之一。在以前的工作中，根据不同的临界距离理论预测了具有不同结构特征的曲轴的疲劳极限载荷。结果表明，TCD的定义对此类预测的准确性有明显影响。本文首先根据给定曲轴的极限应力分布和方法的定义确定了临界距离。然后，根据上一步获得的参数预测另一个曲轴的疲劳极限载荷。最后，进行了相应的实验验证和模型参数误差影响分析，以评估预测的准确性。结果表明，对于改进的间接定义TCD（ITCD），基于线和点方法的预测近似相等，并且参数误差对预测有明显影响。但是，对于直接定义的TCD（DTCD），临界线方法比临界点方法具有更好的准确性，并且DTCD对模型参数误差的敏感度比ITCD方法低得多，因此，DTCD方法更适合实际工程应用。