DESIGN AND TECHNOLOGICAL METHODS OF INCREASING THE LOW-CYCLE FATIGUE LIFE OF WELDED STRUCTURES

i. Structural and Chemical Macro- and Microinhomogeneity of the Metal. The macroinhomogeneity is related to the presence of thecast metal of the joint, the heat-affected zone with a series of transition structures, and the base metal not subjected to the action of welding while the microinhomogeneity is caused by the presence of grains, grain boundaries, phases, inclusions, etc. within the limits of each zone of the weld joint. 2. Inhomogeneity in the elastoplastic stressed condition caused by nonuniform distribution of the residual deformations in the weld joint and also by stress and deformation concentration from the external load as the result of geometric nonuniformity of the weld joint. 3. Geometric nonuniformity related to the presence of: a) external factors of the joint form (poor penetration, undercuts, reinforcements, cold laps, cracks, etc.); b) internal defects (cracks, voids, etc.); c) design stress raisers, which are dependent upon the configuration and type of the weld joint (butt, T-joint, lap, etc.). In fundamental works devoted to the fatigue of weld joints, consideration is given primarily to questions of normal, multicycle fatigue [3-6], while many structures operate under conditions of significant low-frequency loads, that is, under low-cycle loading.