Fatigue crack growth thresholds for ferritic steels and aluminum alloys in flaw evaluation documents are reviewed. The WRC (Welding Research Council) Bulletin, ASME (American Society of Mechanical Engineers) Code Section VIII, IIW (International Institute of Welding) and BS (British Standards) 7910 give constant fatigue crack growth threshold values at negative stress ratios. However, the definitions of the thresholds at negative stress ratios are different between these flaw evaluation documents. From fatigue crack growth tests and collection of fatigue crack growth threshold data, the thresholds are affected by compressive stresses. It can be said that the thresholds at negative stress ratios are not constant. Therefore, the thresholds given by the WRC Bulletin, ASME Section VIII and IIW are slightly un-conservative. The threshold given by BS 7910 is considerably conservative. A suitable definition of the threshold at negative stress ratios for application in flaw evaluation procedures is proposed as the variable threshold expressed by full range of stress intensity factors.

审查了缺陷评估文件中铁素体钢和铝合金的疲劳裂纹扩展阈值。WRC（焊接研究委员会）公告，ASME（美国机械工程师学会）法规第VIII节，IIW（国际焊接学会）和BS（英国标准）7910在负应力比下给出了恒定的疲劳裂纹扩展阈值。但是，在这些缺陷评估文档之间，负应力比下的阈值定义不同。通过疲劳裂纹扩展测试和疲劳裂纹扩展阈值数据的收集，该阈值受压缩应力的影响。可以说，负应力比下的阈值不是恒定的。因此，WRC公告，ASME第八节和IIW给出的阈值有些保守。BS 7910给出的阈值相当保守。提出了一种适用于缺陷评估程序的负应力比阈值的合适定义，该变量阈值由应力强度因子的全部范围表示。