Abstract: Aiming at the problem of accurate analysis for fatigue life of large modulus rack, the propagation of crack for large modulus quenched rack was studied. A FRANC3D model of the rack with initial collinear double cracks was established, the meshing area of rack was divided into 15 area foods. The influence of surface induction quenching rack hardness distribution and residual compressive stress distribution on fatigue crack propagation life was analyzed, and the fracture toughness KIC and the threshold value of stress intensity factor ΔKth of the rack were derived. With FRANC3D, the process of crack propagation, connection and continuous propagation under three horizontal spacing was simulated, and the expression of stress intensity factor amplitude ΔK with crack depth a was obtained. In accordance with the relationship between crack growth rate da/dN and ΔK, KIC, ΔKth, the residual fatigue life of rack in the Three Gorges ship lift N was predicted. The results indicate that the rack meets the fatigue requirements. However, the fatigue life of the rack is reduced, the effect of hardness distribution on the crack growth is greater than that of the residual compressive stress.
Key words: large modulus crack; surface quenching; FRANC3D; stress intensity factor; fatigue propagation life