Fatigue Crack Growth Behavior of Friction Stir Welded 2024-T3 Aluminum Alloy Tested Under Accelerated Salt Fog Exposure PDF Download
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Author: M. Milan
Publisher:
ISBN:
Category : Aluminum
Languages : en
Pages : 20
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Book Description
Fatigue crack growth properties of friction stir welded joints of 2024-T3 aluminum alloy were studied via constant amplitude load (increasing ?K) testing under open air and accelerated salt fog exposure conditions. For low ?K values, longitudinal crack growth in the weld line center was slower under corrosion fatigue than by air because of the prevalence of corrosion-induced crack closure. On the other hand, growth rates of transverse crack crossing the weld nugget were not affected by the environment aggressiveness because of a balance between hydrogen embrittlement and corrosion inducing crack closure along with welding compressive residual stresses. For intermediate ?K values, propagation rates 5 times faster were observed for both longitudinal and transverse cracks under salt fog ambient as a result of hydrogen-induced embrittlement, which is favored by larger crack tip openings allowing local corrosive medium access. As the final catastrophic fracture approaches, longitudinal and transversal crack propagation rates under corrosion fatigue approximated the values observed in air testing, as time, under the 30-Hz loading frequency applied, was scarce for an effective interaction between crack tip fresh material and the hostile environment. For longitudinal cracks, precracking in air resulted in fatigue-corrosion limit factor ?Kth slightly lower than that obtained in salt fog precracked specimens, as the corrosive role played by the salt fog environment along the precrack introduction contributed to crack-closure effect, so increasing the apparent value of ?Kth. On the other hand, the environment in which a transverse precrack was created had a negligible effect on ?Kth because of the establishment of an equilibrium condition between corrosion-induced precrack closure and hydrogen embrittlement.
Author: M. Milan
Publisher:
ISBN:
Category : Aluminum
Languages : en
Pages : 20
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Book Description
Fatigue crack growth properties of friction stir welded joints of 2024-T3 aluminum alloy were studied via constant amplitude load (increasing ?K) testing under open air and accelerated salt fog exposure conditions. For low ?K values, longitudinal crack growth in the weld line center was slower under corrosion fatigue than by air because of the prevalence of corrosion-induced crack closure. On the other hand, growth rates of transverse crack crossing the weld nugget were not affected by the environment aggressiveness because of a balance between hydrogen embrittlement and corrosion inducing crack closure along with welding compressive residual stresses. For intermediate ?K values, propagation rates 5 times faster were observed for both longitudinal and transverse cracks under salt fog ambient as a result of hydrogen-induced embrittlement, which is favored by larger crack tip openings allowing local corrosive medium access. As the final catastrophic fracture approaches, longitudinal and transversal crack propagation rates under corrosion fatigue approximated the values observed in air testing, as time, under the 30-Hz loading frequency applied, was scarce for an effective interaction between crack tip fresh material and the hostile environment. For longitudinal cracks, precracking in air resulted in fatigue-corrosion limit factor ?Kth slightly lower than that obtained in salt fog precracked specimens, as the corrosive role played by the salt fog environment along the precrack introduction contributed to crack-closure effect, so increasing the apparent value of ?Kth. On the other hand, the environment in which a transverse precrack was created had a negligible effect on ?Kth because of the establishment of an equilibrium condition between corrosion-induced precrack closure and hydrogen embrittlement.
Author: J. Brian Jordon
Publisher: Butterworth-Heinemann
ISBN: 0128163054
Category : Technology & Engineering
Languages : en
Pages : 198
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Book Description
Fatigue in Friction Stir Welding provides knowledge on how to design and fabricate high performance, fatigue resistance FSW joints. It summarizes fatigue characterizations of key FSW configurations, including butt and lap-shear joints. The book's main focus is on fatigue of aluminum alloys, but discussions of magnesium, steel, and titanium alloys are also included. The FSW process-structure-fatigue performance relationships, including tool rotation, travel speeds, and pin tools are covered, along with sections on extreme fatigue conditions and environments, including multiaxial, variable amplitude, and corrosion effects on fatigue of the FSW. From a practical design perspective, appropriate fatigue design guidelines, including engineering and microstructure-sensitive modeling approaches are discussed. Finally, an appendix with numerous representative fatigue curves for design and reference purposes completes the work. - Provides a comprehensive characterization of fatigue behavior for various FSW joints and alloy combinations, along with an in-depth presentation on crack initiation and growth mechanisms - Presents the relationships between process parameters and fatigue behavior - Discusses modeling strategies and design recommendations, along with experimental data for reference purposes
Author: Robert S. Piascik
Publisher:
ISBN:
Category : Aluminum alloys
Languages : en
Pages : 34
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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 14
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Author: National Aeronautics and Space Adm Nasa
Publisher: Independently Published
ISBN: 9781792718212
Category :
Languages : en
Pages : 28
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Book Description
Fatigue crack growth tests were conducted on 0.09 inch thick, 3.0 inch wide middle-crack tension specimens cut from sheets of 2024-T3 aluminum alloy. The tests were conducted using a load sequence that consisted of a single block of 2,500 cycles of constant amplitude loading followed by an overload/underload combination. The largest fatigue crack growth life occurred for the tests with the overload stress equal to 2 times the constant amplitude stress and the underload stress equal to the constant amplitude minimum stress. For the tests with compressive underloads, the fatigue crack growth life decreased with increasing compressive underload stress. Dawicke, David S. Langley Research Center NASA-CR-201668, NAS 1.26:201668 NAS1-96014; RTOP 538-02-10-01...
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 11
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Author: EP. Phillips
Publisher:
ISBN:
Category : Aluminum alloys
Languages : en
Pages : 11
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Book Description
Crack opening loads were determined in load-shedding fatigue crack growth threshold tests on 2024-T3 aluminum alloy at stress ratios R of -2, -1, 0, 0.33, 0.5, and 0.7. The effects of load-shedding procedure and rate were investigated. Values of threshold ?K were found to vary significantly with R, whereas values of threshold effective ?K did not. That is, the variation of threshold ?K with R was almost completely explained by accounting for the measured variation in crack opening load behavior with R. The load-shedding guidelines of ASTM Test Method for Measurement of Fatigue Crack Growth (E 647) produced a threshold ?K value for R = 0.7 that was in agreement with the value determined using a procedure that should minimize closure effects (constant-Kmax, increasing-Kmin test). At both R = 0 and R = 0.7, high load-shedding rates produced high values of threshold ?K caused by large closure effects.
Author: National Aeronautics and Space Administration (NASA)
Publisher: Createspace Independent Publishing Platform
ISBN: 9781722867089
Category :
Languages : en
Pages : 32
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Book Description
The corrosion fatigue crack growth characteristics of small surface and corner cracks in aluminum alloy 2024 is established. The damaging effect of salt water on the early stages of small crack growth is characterized by crack initiation at constituent particle pits, intergranular microcracking for a less than 100 micrometers, and transgranular small crack growth for a micrometer. In aqueous 1 percent NaCl and at a constant anodic potential of -700 mV(sub SCE), small cracks exhibit a factor of three increase in fatigue crack growth rates compared to laboratory air. Small cracks exhibit accelerated corrosion fatigue crack growth rates at low levels of delta-K (less than 1 MPa square root of m) below long crack delta-K (sub th). When exposed to Paris regime levels of crack tip stress intensity, small corrosion fatigue cracks exhibit growth rates similar to that observed for long cracks. Results suggest that crack closure effects influence the corrosion fatigue crack growth rates of small cracks (a less than or equal to 100 micrometers). This is evidenced by similar small and long crack growth behavior at various levels of R. Contrary to the corrosion fatigue characteristics of small cracks in high strength steels, no pronounced chemical crack length effect is observed for Al by 2024 exposed to salt water. Piascik, Robert S. and Willard, Scott A. Langley Research Center RTOP 538-02-10-01...
Author: Robert G. Dubensky
Publisher:
ISBN:
Category : Aluminum alloys
Languages : en
Pages : 36
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Author: Patrick Joseph Cain
Publisher:
ISBN:
Category :
Languages : en
Pages : 256
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