The influence of welding-induced 3D residual stress and distortion on the ultimate strength of multi-stiffened thin plate structures under cyclic load

Abstract

Stiffened thin plates made of high-strength steel are widely employed in ship hull structures. Their strength capacity is highly sensitive to the welding imperfections and potential extreme cyclic loading from harsh sea state. In this work, a thermal elasto-plastic finite element analysis is conducted to simulate the 3D distribution of welding-induced residual stress and distortion of stiffened thin plate structures with triple spans and triple bays varying the plate thickness and heat input. Experimental results provided by other scholars are used to validate the welding simulation. Afterwards, the ultimate strength and collapse behaviour of the welded structures under different load patterns are dealt with, including monotonic compression load, cyclic compression-tension load and cyclic compression load. Observation from numerical results indicates that, in general, the compressive strength is reduced in each considered cycle by the residual stress as the amplitude of cyclic compression-tension load approximates to the ultimate compressive strain. When this parameter is much greater than the ultimate compressive strain or the stiffened plate is subjected to cyclic compression load, the reduction in ultimate strength is significant in the first cycle, whereas the reduction is ignorable in the later cycles. Besides, if the buckling mode of initial deflection with antisymmetric configuration is superposed to the symmetric out-of-plane welding distortion, impact of the residual stress will be diminished as the asymmetry becomes notable.