Effect of the structure of the end zone of crack in unstable material on durability and crack resistance under low-cyclic loading

Structure of the end zone of crack in the deformed unstable material under conditions of low-cyclic loading is experimentally studied and its effect on durability and crack resistance is estimated. The methods of X-ray and metallographic analysis have shown that the end zone of the crack consists of some regions differing in size of crystallites, density of shear and dislocation lines. Secondary high-strength phase interacting with a matrix one is isolated from the matrix phase of low strength as a result of the action of variable stresses of high level in the region adjacent to the crack apex (the prefailure zone). The presence of the secondary phase leads to an essential increase of the material durability, the value of the critical length of the crack and breaking stress.