Estimating the endurance of structural elements with microcracks and residual welding stresses

The quality of technological and welding processes of ship structures largely determines their reliability under cyclic loads. To ensure the fatigue strength of structural elements during the operation of vessels certain methods are needed which allow ongoing monitoring, assessing and forecasting their technical condition promptly and with minimal costs. Such methods must take into consideration the real stress state of structures, the type of loading, the residual welding stresses, the effect of concentrators, and fatigue changes in the structure of steel depending on the period of the ship’s exploitation. The paper presents a calculation technique to estimate the fatigue strength of welded structures with residual stresses and concentrators. There has been performed an integrated analysis of the effect that the compressive and tensile residual welding stresses creating a multiaxial stressed state make on the fatigue strength of welded joints. Presented are the profile of the welded corner joint from the position of the minimum stress concentration and the simple calculation dependence for estimating the endurance limit by the geometric dimensions of the welded joints section and the theoretical stress concentration coefficients. There has been developed a calculation model for low-cycle fracture which makes it possible to estimate the endurance limits through the criterion of the appearance of macrocracks in structures with technological stress concentrators. The obtained results may be used to assess the reliability of welded joints of structures with stress concentration, residual welding stresses and the structural damages of ship structures. The level of the nominal external load not engendering cracks in the concentrator and referring to the yield strength can serve as a criterion characterising the ability of the material to withstand cracking in welded joints