Microstructure-Based Fatigue Life Prediction Methods for Naval Steel Structures

摘要

The goal of the subject program has been to develop fundamental understandings ofthe relationships between microstructure and fatigue damage in structural steels of interest to naval applications. Quantitative descriptions of these relationships have been incorporated within practical engineering models for the prediction of fatigue life. Fatigue damage associated with microcrack nucleation and growth has been studied experimentally with S-N fatigue specimens of HSLA-80 steel. Some microstructures were modified with appropriate heat treatments, and the effects of microstructure on microcrack nucleation and growth have been characterized. Microstructural scaling laws have been developed and verified for both fatigue crack growth (FCG) and smooth specimen total life in a wide range of steels. The effects of microstructure on FCG have been described by a dimensionless microstructural parameter which is defined in terms of stress, fatigue ductility, dislocation cell size, and dislocation barrier spacing. FCG data from large and small flaws have been critically compared on the basis of engineering models for FCG rates, and the implications of this comparison for engineering fatigue life prediction are explored. A probabilistic treatment of the micromechanical scaling laws for FCG has been derived, permitting a direct evaluation of the relationship between microstructural variation and variability in FCG rates. HSLA Steels, Fatigue life prediction, Fatigue crack growth, Small cracks, Modeling, Microstructure, Copper precipitates, Probabilistic fracture mechanics, Welded structures.