Use of the concept of specific fracture work to evaluate the cyclic fracture toughness of steels

1. The physical singificance of the relationship between the two material constants C and n $$C = \frac{{1,03.10^{ - 4} }}{{861^n }}$$ in the Paris-Erdogan equation describing section II of a kinetic fatigue curve $$\frac{{da}}{{dN}} = C(\Delta K)^n $$ is that the resistance of the material to fatigue crack propagation at this stage is determined by a single but complex characteristic of the properties of the material—specific fracture work. 2. The cyclic fracture toughness of materials can be evaluated by using fracture work, which includes both ductility and strength characteristics of the material. The specific fracture work is determined by testing smooth specimens in tension. 3. Study of steels of different compositions and structures established the relationship between the exponent n in the Paris-Erdogan equation and specific fracture work Wc: $$n = (5,0652 \pm 0,1168) - (0,00168 \pm 0,0001W_c ).$$ 4. There is no unambiguous relationship between the value of ΔKth, characterizing the resistance of materials to the initiation of a fatigue crack, and specific fracture work. The lack of such a relationship is confirmed by the absence of a link between specific fracture work and the endurance limit.