Life-Cycle Fatigue Reliability of Ship Structures: A Proposed System

Abstract

Fatigue damage of structural details in essence may be attributed to the consequences of the traditional approach of securing the reliability of structures when the design and maintenance are provided by different groups of experts with different principles and different professional training. Progress may be achieved when the whole life-cycle reliability of a structure is provided uniformly in the design and service cycles. A series of actions and appropriate fatigue models composing an automated system to aid in the design and maintenance of ship structures is proposed. Considering the existing and feasible actions, attention is focused on the fatigue design and post-fabrication assessment of fatigue properties at critical locations.

Strain-Life Approach: Application for Fatigue Design of Ship Superstructure Critical Detail

“…The following step in the procedure is the evaluation of the elastic-plastic cyclic strain, ε ∆ , at a critical location. Neither the inelastic finite-element analysis facilities nor the Neuber's heuristic formula-based approach [6] are used here. Instead, conditional generalized cyclic diagram of steel under the scope is applied.…”

“…Instead, conditional generalized cyclic diagram of steel under the scope is applied. Such diagrams for hull steels were derived based on the parametric experimental studies of local strain evolution at varied stress concentration, nominal stress amplitude and mean stress [6]. Analysis of test results revealed similitude of material cyclic behavior which allowed deriving the cyclic diagrams, strain range at the notch root related to nominal stress range in a structural component: , = + 0 1 ; here t is the thickness of the notched component, r is the notch root radius, M 0 , a , s and q are empirical parameters; ( )…”

Adaptive Finite Element Model for Simulating Crack Growth in the Presence of Holes

“…Fatigue cracks in redundant structures often show retarded growth under moderate stress, allowing part of the crack growth to be included in the range of reasonable service life, but only if crack growth can be accurately estimated, monitored, and affected details fixed before the beginning of a critical structural situation. The potential of incorporating a portion of crack extensions in the service life of components provides the foundation for the development of the design principle known as "damage tolerant design," which relates to components that are designed to operate with fatigue damage in a permissible limit [3].…”

Two-Dimensional Surface Fatigue Crack Propagation and its Finite Element Simulation

“…In redundant structures at moderate stress fatigue cracks are typically grow slowly which allows including part of the crack propagation into the range of reasonable service life, however, on condition that crack growth may be reliably predicted, monitored and affected detail repaired before the onset of critical condition of the structure. The prospect of including a certain part of the crack extensions into the service life of structures constitute a base for development of the design concept, "damage-tolerant design", design of structures for operation with allowed fatigue damage within safe limits [2].…”