Low Cycle Fatigue Crack Propagation Resistance of Materials for Large Welded Structures

The development and application of modern, higher strength materials for large welded structures, combined with the realization that flaw-free fabrication cannot be ensured, have created a need for methods to evaluate the low cycle fatigue crack propagation resistance of structural metals. In this paper a test method is discussed which has been applied to a broad spectrum of structural metals, both ferrous and nonferrous, including yield strengths from 30 to 200 ksi. The results apply to structural lives ranging from 100 to 100,000 cycles. Data are presented in terms of an empirical power-law relationship between fatigue crack growth rate and total (elastic plus plastic) strain range. Comparisons are made among the low cycle fatigue crack propagation characteristics of competitive materials, and a first-order translation of crack growth rates to an index of structural fatigue life is developed. The influences of aqueous environments and mean strain are described.