Activation Energy Dependence on Stress Intensity in Stress-Corrosion Cracking and Corrosion Fatigue

2009 ◽  
pp. 157-157-19 ◽  
Author(s):  
PJ Bania ◽  
SD Antolovich
Keyword(s):  
Activation Energy ◽  
Stress Intensity ◽  
Stress Corrosion ◽  
Energy Dependence ◽  
Corrosion Fatigue ◽  
Stress Corrosion Cracking ◽  
Corrosion Cracking

Corrosion Fatigue Crack Growth Rates of Sensitized AA5456-H116: Contribution of Stress Corrosion Cracking

CORROSION ◽  
10.5006/3682 ◽  
2020 ◽  
Author(s):  
David Schrock ◽  
Allison Akman ◽  
Jenifer Locke
Keyword(s):  
Fatigue Crack ◽  
Stress Intensity ◽  
Aluminum Alloys ◽  
Fatigue Crack Growth ◽  
Stress Corrosion ◽  
Corrosion Fatigue ◽  
Stress Corrosion Cracking ◽  
Inverse Relationship ◽  
Corrosion Cracking ◽  
Crack Growth Rates

The interplay between stress corrosion cracking (SCC) and corrosion fatigue was investigated for AA5456-H116 to determine the source of the inverse relationship between fatigue loading (f) and fatigue crack growth rates (da/dN). Sensitization in 5xxx series aluminum alloys refers to the precipitation of β on α-Aluminum grain boundaries, which can occur in high-Mg 5xxx alloys after sufficient exposure to temperatures as low as 40 °C. Recent research has established that da/dN in sensitized 5xxx series aluminum alloys can be inversely dependent on f. The severity of the inverse relationship between da/dN and f has been attributed to sensitization level, alloy composition, and temper. In this work, the effect that K<sub>max</sub> has on corrosion fatigue da/dN was quantified using fracture mechanics-based experiments conducted at different maximum stress intensity factors (K<sub>max</sub>) but the same ΔK in 3.5 wt.% NaCl. Results suggest that the severity of the inverse relationship between da/dN and f (i.e., the slope of the da/dN versus f trend) is governed by the magnitude of K<sub>max</sub> in relation to the threshold stress intensity factor for stress corrosion cracking (K<sub>ISCC</sub>). In addition, results show that an inverse f-dependence, albeit with a lower slope, can exist even when K<sub>max</sub> is less than K<sub>ISCC</sub>; in other words, absent SCC. This low-slope corrosion fatigue behavior may have been driven by an enhanced rate of hydrogen embrittlement facilitated by the more aggressive local crack tip environment present at progressively lower loading frequencies during corrosion of highly sensitized microstructures.

A New Generalized Nonlinear Superposition Theory and its Applications in Modeling Corrosion-Fatigue

2013 ◽  
Author(s):  
Zhigang Wei ◽  
Limin Luo ◽  
Marek Rybarz ◽  
Kamran Nikbin
Keyword(s):  
Synergistic Effect ◽  
Stress Corrosion ◽  
Corrosion Fatigue ◽  
Stress Corrosion Cracking ◽  
Failure Mechanisms ◽  
Corrosion Cracking ◽  
Time Dependent ◽  
Linear Superposition ◽  
Nonlinear Superposition ◽  
Cycle Dependent

Corrosion-fatigue and stress corrosion cracking have long been recognized as the principal degradation and failure mechanisms of materials under combined corrosive environment and sustained/cyclic loading conditions. These phenomena are strongly material and environment dependent, and cycle-dependent fatigue and time-dependent matter diffusion/chemical reaction at the crack tip can be operational simultaneously. How to include these cycle-dependent and time-dependent phenomena in a single model and how to study the failure mechanisms interaction are big challenges posed to material scientists and engineers. In this paper the current linear superposition theories for modeling cycle-dependent and time-dependent corrosion-fatigue and stress corrosion cracking phenomena are reviewed first. Subsequently, a generalized nonlinear superposition theory is proposed to incorporate possible nonlinear interaction or synergistic effect among the underlying mechanisms. The unified model derived from the new theory, depending on the specific materials and loading condition and environment, can be reduced to pure corrosion, pure fatigue, stress corrosion cracking and corrosion-fatigue. Finally, for the first time, a new breakthrough parameter is defined in this paper to quantitatively describe the interaction or synergistic effect between two different operating mechanisms, such as time- and cycle-dependent mechanisms.

The role of crack branching in stress corrosion cracking of aluminium alloys

2015 ◽  
Vol 33 (6) ◽  
pp. 443-454 ◽  
Author(s):  
Timothy L. Burnett ◽  
N.J. Henry Holroyd ◽  
Geoffrey M. Scamans ◽  
Xiaorong Zhou ◽  
George E. Thompson ◽  
...  
Keyword(s):  
Stress Intensity ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Aluminium Alloys ◽  
Compact Tension ◽  
Corrosion Cracking ◽  
Three Dimensions ◽  
Crack Branching ◽  
Test Procedures ◽  
The Many

AbstractStress corrosion cracks of all types are characterised by extensive crack branching, and this is frequently used as the key failure analysis characteristic to identify this type of cracking. For aluminium alloys, stress corrosion cracking (SCC) is almost exclusively an intergranular failure mechanism. For plate and extruded components, this had led to the development of test procedures using double cantilever beam and compact tension precracked specimens that rely on the pancake grain shape to constrain cracking, so that fracture mechanics can be applied to the analysis of stress intensity and crack velocity and the evolution of a characteristic performance curve. We have used X-ray computed tomography to examine in detail SCC in aluminium alloys in three dimensions for the first time. We have found that crack branching limits the stress intensity at the crack tip as the applied stress is shared amongst a number of cracks that are held together by uncracked ligaments. We propose that the plateau region observed in the v-K curve is an artefact due to crack branching, and at the crack tips of the many crack branches, cracking essentially occurs at constant K almost irrespective of the crack length. We have amplified the crack branching effect by examining a sample where the long axis of the pancake grains was inclined to the applied stressing direction. Our results have profound implications for the future use of precracked specimens for SCC susceptibility testing and the interpretation of results from these tests.

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