Failure of OT4-1 and D16T alloys during cyclic loading over a wide range of frequencies

Abstract

1. For both forms of loading over the whole range of working frequencies nucleation and propagation of the fatigue crack in OT4-1 alloy is observed in a direction perpendicular to the action of the applied tensile stresses, i. e., in this case nucleation and development of the crack are of the normal breaking crack type. 2. In D16T alloy for both forms of loading over the whole range of working frequencies the fatigue crack is nucleated similarly to the normal breaking crack, and the length of the section of the nucleating crack normal to the main tensile stress decreases with increase in the amplitude of the cyclic stress. The fatigue crack develops at an angle of 45° to the main tensile stress, and this corresponds to a transverse shear type of crack. 3. During uniform extension-compression the propagation rate of the crack in the cycle dl/dN in its nucleating part is lower for D16T alloy than for OT4-1 alloy. 4. For both materials under conditions of uniform extension-compression change in the loading frequency has little effect on the velocity of the crack in the cycle. 5. In the case of high loading frequencies the relief of the fracture in the investigated alloys is smoother on account of increase in the ductility under the influence of local heating of microvolumes of the material.