DUCTILE FAILURE CRITERION FOR MARINE ENGINEERING STRUCTURES

Welded marine engineering structures operating under ordinary and low (- 40 degrees C and lower) temperatures are studied. To justify required safety margins, new international and home standards regulating strength and reliability issues for Arctic oil-and-gas structures require structural ultimate strength analysis with account of possible low-temperature plasticity and fracture strength decrease of materials and welded connections. To realize these requirements, preliminary solution of fundamental methodical issues of analysis of structural failure in the stress concentration areas under the limit equilibrium is required. The maximum plasticity decrease caused by stressed state three-dimensionality is normally observed in structural details; in this connection there is a necessity of using the finite-element method to analyze this state and formulating a corresponding criterion of occurring crack-like defects with account of state-of-art achievements in the fracture mechanics. Therefore, the paper objective consists in development of reliable ductile failure criteria suitable for direct finite element analysis of welded structures for static strength with account of actually reached material plasticity and fatigue strength indexes for the base metal and welded connections. The following results have been obtained based on the performed studies: a new integral ductile failure criterion has been developed for evaluation of ultimate structural strength; by comparison of calculated and experimental data it has been demonstrated that use of this criterion instead of conventional ones provides considerable accuracy increase for structural ultimate strength analysis. Based on the developed new ductile failure criterion, a new approach to marine engineering strength analysis has been created that is an important element of the reliability system, operating safety and the technology for structures of Arctic vessels and ocean engineering structures.