The influence of microstructure on the fatigue crack growth rate in marine steels in the Paris Region

Victor Igwemezie,Feargal Brennan,Ali Mehmanparast

doi:10.1111/ffe.13312

Abstract

AbstractThis paper presents a study on the effect of microstructure on the fatigue crack growth (FCG) rate in advanced S355 marine steels in the Paris Region of the da/dN versus ΔK log–log plot. The environments of study were air and seawater (SW), under constant amplitude sinewave fatigue loading. Fundamentally, three phenomena (crack tip diversion, crack front bifurcation and metal crumb formation) were observed to influence the rate of FCG. These phenomena appear to be a function of the material microstructure, environment and crack tip loading conditions. The three factors retarded the crack growth by reducing or redistributing the effective driving force at the main active crack tip. A crack path containing extensively the three phenomena was observed to offer strong resistance to FCG. In SW, the degree of the electrochemical dissolution of the microplastic zone appears to be an additional primary factor influencing FCG in the steels.

Highlights

Understanding how a crack propagates in a given material is fundamental to all forms of theoretical postulations, modelling, analytical and numerical analyses
Environment and loading condition are such that the three phenomena are extensive, crack growth retardation occurs; otherwise, the rate may increase
This study investigated the influence of microstructure on the FCG rate (FCGR) in advanced marine steels in the Paris Region, both in air and SW under sinewave fatigue loading

Summary

Introduction

Understanding how a crack propagates in a given material is fundamental to all forms of theoretical postulations, modelling, analytical and numerical analyses. Note that the microstructures of G8 and G10 are generally the FIGURE 1 2 (A) Fatigue crack path in J2N steel in air (10 kN, 5 Hz) and (B) schematic of the crack path (direction: from left to right) [Colour figure can be viewed at wileyonlinelibrary.com]

Results

Conclusion