Quantitative models on corrosion fatigue crack growth rates in metals: Part I. Overview of quantitative crack growth models

Abstract

Approaches to predict da/dN-AK for environmental situations; including empirical interpolative equations, linear superposition of mechanical fatigue and time-based environmental cracking, and mechanism-based models; are presented. For several material-environment systems, these models were incorporated in fracture mechanics life prediction methods, and successes have been reported in evaluating the corrosion fatigue contribution. Considerable uncertainties are, however, associated with these models. The linear superposition analysis is emphasized; material-environment systems that are severely environment-sensitive should be adequately described by this method. Direct and indirect methods exist to define time-based crack growth rates for use in linear superposition predictions of da/dN. The linear superposition approach is effective, but only for those cases where K~s{x: is high relative to typical flawed component stress intensity levels. Empirical curve-fit models require an extensive environmental crack growth rate data base, which are costly to develop, and are effective for interpolations but not predictions of fatigue crack growth data. Mechanism-based models for broad predictions of cycle-time dependent da/dN versus AK, and other variables such as frequency or hold time, are in an infant state.

Interaction of Cyclic Loading (Low‐Cyclic Fatigue) with Stress Corrosion Cracking (SCC) Growth Rate

“…e simplest and empirical approach is the linear superposition method for the crack growth rate. It was first given by Wei, Landes, Gallagher, and Bucci [44]. According to superposition method, the environment enhanced equivalent/overall crack growth rate (sum of SCC and fatigue crack growth rate), [da/dN o ] m , is given by combining the inert fatigue crack growth rate, da/dN m , and time-dependent, monotonic load environment crack growth rate, da/dN Scc , that is,…”

Corrosion fatigue crack growth modelling for subsea pipeline steels

“…And the influences of high frequencies on the crack growth rate plateau are predicted better than those of low frequencies. Other models (Kim et al, 1998) modified these assumptions mostly by adding parameters.…”

“…Although theoretical and experimental studies on SCC are relatively ample, CF is receiving more and more attention in recent years. A number of models have been developed for CF of metals in aqueous environments (Kim et al, 1998). However, most of them are just phenomenological because the material's CF cracking behavior is quite complicated and considerable variables can impose their impacts, while the involved mechanisms are not very clear.…”

Influence de l'environnement sur la propagation des fissures de fatigue

“…La fissuration en solution aqueuse peut donner naissance à de nouvelles sources de fermeture de fissure, principalement par effet « coin », dues à la compression du liquide environnant [78,79], aux produits de corrosion [75,78,80,81] mais aussi aux grains déchaussés ou détachés de la pointe de fissure par corrosion intergranulaire [78]. On définit ici les produits de corrosion comme les espèces résultant des réactions entre le métal et le milieu et présentes en solution, contrairement à un oxyde qui se crée à la surface du métal.…”

“…En effet il convient de décomposer la fréquence en deux paramètres : la période totale du cycle, déterminant la durée d'exposition, et la vitesse de chargement. De nombreuses études font ressortir l'importance de la vitesse de chargement lorsque la synergie entre les mécanismes de fatigue et la corrosion est grande [69,90,93,95], tandis que la durée d'un cycle peut avoir beaucoup d'influence lorsque la corrosion sous contrainte est susceptible de s'ajouter à l'endommagement de fatigue, en particulier si le seuil de fissuration en corrosion sous contrainte K ISCC est dépassé [78] (comportement de type b) et c) Figure 10). …”