Journal ArticleDOI
Mechanisms of Slow Fatigue Crack Growth in High Strength Aluminum Alloys: Role of Microstructure and Environment
TLDR
In this article, the role of microstructure and environment in influencing ultra-low fatigue crack propagation rates has been investigated in 7075 aluminum alloy heat-treated to underaged, peak-aged, and overaged conditions and tested over a range of load ratios.Abstract:
The role of microstructure and environment in influencing ultra-low fatigue crack propagation rates has been investigated in 7075 aluminum alloy heat-treated to underaged, peak-aged, and overaged conditions and tested over a range of load ratios. Threshold stress intensity range, ΔK0, values were found to decrease monotonically with increasing load ratio for all three heat treatments fatigue tested in 95 pct relative humidity air, with ΔK
0 decreasing at all load ratios with increased extent of aging. Comparison of the near-threshold fatigue behavior obtained in humid air with the data forvacuo, however, showed that the presence of moisture leads to a larger reduction in ΔK0 for the underaged microstructure than the overaged condition, at all load ratios. An examination of the nature of crack morphology and scanning Auger/SIMS analyses of near-threshold fracture surfaces revealed that although the crack path in the underaged structure was highly serrated and nonlinear, crack face oxidation products were much thicker in the overaged condition. The apparent differences in slow fatigue crack growth resistance of the three aging conditions are ascribed to a complex interaction among three mechanisms: the embrittling effect of moisture resulting in conventional corrosion fatigue processes, the role of microstructure and slip mode in inducing crack deflection, and crack closure arising from a combination of environmental and microstructural contributions.read more
Citations
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Journal ArticleDOI
Friction-stir welding effects on microstructure and fatigue of aluminum alloy 7050-T7451
TL;DR: In this paper, the effects of friction-stir welded aluminum alloy 7050 in a T7451 temper to investigate the effects on the microstructure and mechanical properties were investigated.
Journal ArticleDOI
A review of crack closure, fatigue crack threshold and related phenomena
TL;DR: In this article, a new model was proposed to rationalize the observed variations in the fatigue crack threshold with load ratio, which is based on a requirement for two critical stress intensity parameters, namely ΔK th ∗ and K max ∗, that must be satisfied simultaneously as the crack tip driving forces for fatigue crack growth.
Journal ArticleDOI
Residual stress effects on near-threshold fatigue crack growth in friction stir welds in aerospace alloys
TL;DR: In this article, a study on near-threshold fatigue crack growth in friction stir welded aluminum alloy 7050-T7451 and a titanium alloy Ti-6Al-4V is presented.
Journal ArticleDOI
Fatigue crack deflection and fracture surface contact: Micromechanical models
TL;DR: In this paper, a simple linear elastic analysis of tilted cracks is proposed to estimate the variation of cyclic crack propagation rates under the combined influence of crack kinking and fracture surface contact.
Journal ArticleDOI
Laser and shot peening effects on fatigue crack growth in friction stir welded 7075-T7351 aluminum alloy joints
TL;DR: In this article, the influence of shot and laser peening on the fatigue crack growth behavior of friction stir welded (FSW) aluminum alloy (AA) 7075-T7351 sheets was investigated.
References
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Journal ArticleDOI
Oxide-Induced Crack Closure: An Explanation for Near-Threshold Corrosion Fatigue Crack Growth Behavior
TL;DR: The concept of oxide-induced crack closure is utilized to explain the role of gaseous and aqueous environments on corrosion fatigue crack propagation at ultralow, near-threshold growth rates in bainitic and martensitic 2 1/4 Cr-1 Mo pressure vessel steels as mentioned in this paper.
Journal ArticleDOI
A geometric model for fatigue crack closure induced by fracture surface roughness
Subra Suresh,Robert O. Ritchie +1 more
TL;DR: In this article, a geometric model is presented for crack closure induced by fracture surface roughness, specifically addressing the contribution from both Mode I and Mode II crack tip displacements in addition to considering the nature of the fracture surface morphology.
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Crack deflection: Implications for the growth of long and short fatigue cracks
TL;DR: In this paper, a simple elastic deflection model is developed to estimate the growth rates of nonlinear fatigue cracks subjected to various degrees of deflection, by incorporating changes in the effective driving force and in the apparent propagation rates.
Journal ArticleDOI
Roughness-Induced Crack Closure: An Explanation for Microstructurally Sensitive Fatigue Crack Growth
TL;DR: In this paper, the concept of roughness-induced crack closure is utilized to explain the role of prior austenite grain size and pearlite interlamellar spacing on near-threshold fatigue crack propagation in fully pearlitic eutectoid steel tested at low and high stress ratio in lab air and purified helium.