Kinetic effects in the mechanics of delayed fracture of high-strength alloys

Abstract

1. Kinetic curves for cracking of high-strength alloys in the presence of water and alcohol are not invariant characteristics of the material, but depend on the loading history, especially on the initial values of the coefficient of stress intensity\(K_{I_o } \). 2. By diminishing the rupturing energy of bonds at the crack tip, the medium facilitates SCG. On the other hand, it leads to branching of cracks, thus providing effective stress relaxation and retardation of SCG. The range of ki values at which plateaus are formed on kinetic curves and velocity stabilization is achieved, and also the velocity itself, are determined in great measure by the initial conditions of supply of the medium to the crack tip. From the viewpoint of fracture mechanics, such retardation of crack growth may be interpreted as a reduction in effective coefficients of stress intensity at the tip of a crack having complex morphology. 3. Such factors as loading history and branching of cracks also prove to have a definite effect on the character of kinetic curves in the fatigue of alloys. A substantial difference has been found in the kinetics of fatigue cracks developing with steady increase in values of ΔK as compared with initial values taken within segments I and II of fatigue curves. 4. Control of the branching of cracks must be considered an important means of increasing prolonged crack resistance of alloys.