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Fatigue in Friction Stir Welding


Fatigue in Friction Stir Welding
  • Author : J. Brian Jordon
  • Publisher : Butterworth-Heinemann
  • Release : 2019-02-27
  • ISBN : 9780128163054
  • Language : En, Es, Fr & De
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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

Fatigue of Friction Stir Welded Lap Joints with Sealants


Fatigue of Friction Stir Welded Lap Joints with Sealants
  • Author : Kenneth Thomas Nathaniel Doering
  • Publisher :
  • Release : 2009
  • ISBN : OCLC:436086276
  • Language : En, Es, Fr & De
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"A lack of understanding of corrosion fatigue in friction stir welded aluminum joints prevents friction stir welding from being implemented in aerospace applications. Fatigue testing reveals a 60-75% reduction in the fatigue life of friction stir welded aluminum lap joints immersed in 3.5% NaCl solution (corrosion fatigue) compared with that of lap joints tested in ambient air. The loss in fatigue life is attributed to accelerated fatigue cracking due to hydrogen environment embrittlement. Two polymer sealant candidates are investigated: silicone rubber and nylon-11. Both sealant candidates can be applied prior to welding and seal the faying surface gaps in lap joints upon welding. The rubber sealant cures at room temperature after welding and can be welded with the same parameters as without the sealant. The 50% sample population corrosion fatigue life is increased by 22% with the use of the rubber sealant, but the effectiveness of the rubber sealant is limited by its cohesive mechanical properties, e.g. elongation to failure. In ambient fatigue, the nylon sealed welds exhibit twice the 50% sample population fatigue life of other welds. Finite element modeling predicts a reduction in the stresses in the weld due the stiffness contribution of the nylon sealant. The effectiveness of the nylon sealant is limited by its adhesive bond strength. When immersed in water, as in corrosion fatigue, the adhesive bond strength is reduced, the sealant bond fails within 500 fatigue cycles, and the mechanical benefits of the nylon sealant are negated. The corrosion fatigue life of nylon sealed welds is 26% less than that of welds without sealant because of the more severe hook defect associated with hotter welding conditions required to melt the nylon. Finite element modeling results indicate an increase in stress intensity factors of about 10% in welds with more severe hook defects--Abstract, leaf iii.

Fatigue Crack Growth in Integrally Stiffened Panels Joined Using Friction Stir Welding and Swept Friction Stir Spot Welding


Fatigue Crack Growth in Integrally Stiffened Panels Joined Using Friction Stir Welding and Swept Friction Stir Spot Welding
  • Author : Christian A. Widener
  • Publisher :
  • Release : 2008
  • ISBN : OCLC:1251667550
  • Language : En, Es, Fr & De
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Fatigue crack growth rates in AA2024-T3 sheet joined to AA7075-T6 stiffeners by friction stir welding have been compared with rates measured in panels joined with rivets and in unstiffened parent material panels. Friction stir panels were prepared with both continuous friction stir welding (FSW) and swept friction stir spot welding (FSSW). Fatigue cracks in edge crack panels with continuous FSW joints tended to grow into the parent material away from the stiffeners. This behavior was attributed to the reduced stress levels corresponding to the increased thickness of continuous FSW joints and the support of the attached stiffener. Fatigue cracks in edge crack panels were found to follow the joint line in panels made with discrete fasteners (both rivets and swept FSSW joints). The measured crack growth rates in riveted panels increased at an increasing rate as the crack approached the riveted joints. In contrast, crack growth rates in panels joined with FSSW decreased at a decreasing rate as the crack approached the swept spot joints. Test results indicate that the swept FSSW process produced favorable residual stresses that inhibited fatigue crack growth along the joint line.

Fatigue Behaviour of Aluminum Friction Stir Welds Under Highway Bridge Conditions


Fatigue Behaviour of Aluminum Friction Stir Welds Under Highway Bridge Conditions
  • Author : Shi Hui Guo
  • Publisher :
  • Release : 2018
  • ISBN : OCLC:1057430144
  • Language : En, Es, Fr & De
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Friction stir welding (FSW) is a solid state joining process performed by rotating a cylindrical tool with a short protrusion between the two metal pieces to be joined. The combination of frictional and deformation heating leads to the consolidation of the joint. This welding method is rapidly growing in popularity in many applications, particularly in aluminum alloys for transportation vehicle (rail cars, ships) and bridge applications. Across North America, over 150,000 bridges have been identified as “structurally deficient” or “functionally obsolete”. Since FSW has the potential to have a positive influence on their durability and economics, the Aluminum Association of Canada (AAC) has identified the possibility of replacing promoting aluminum bridge decks as a means of replacing existing deficient concrete decks. However, currently available codes and guidelines for aluminum welded joints only address structures made with conventional welding methods. Therefore, bridge designers are lacking the necessary knowledge to use FSW joints in their designs. The main objective of this thesis is to present a fatigue testing study to support the development of improved “performance-based” code provisions for the quality control and fatigue design of FSW joints by examining the durability of FSW joints with prescribed flaws. In order to obtain the experimental results, various intentionally flawed aluminum FSW samples were fabricated for fatigue testing under constant amplitude (CA) and simulated in-service variable amplitude (VA) loading conditions. A statistical analysis of the results has been performed to assess the influence of the various defect types. It has also been shown how finite element (FE) analysis using the software ABAQUS can be used to assess the influence of the defects on the local stresses within the welded joints. Lastly, it is shown how the fatigue performance of the welds can be predicted using linear elastic fracture mechanics (LEFM). The results of this research will contribute to an improved understanding of the behaviour of imperfect FSW joints under fatigue loading conditions, which simulate in-service vehicular bridge VA loading. The main conclusions of this research include the following: 1) The worst fatigue lives were observed in the specimens with “kissing bond” defects at the weld root (on the order of approximately 1 mm in depth), 2) toe flash, undercut, and worm hole defects, as well as surface improvement by polishing were seen to have a much lower influence on fatigue performance, 3) a novel “lap joint” specimen simulating an extruded bridge deck joint was also observed to fail at the root at a nominal stress level lower than that of a properly-welded butt joint.

Mechanical Metallurgical and Fatigue Properties of Friction Stir Welded and Tungsten Inert Gas Welded AA6061 T6 Aluminium Alloys


Mechanical  Metallurgical and Fatigue Properties of Friction Stir Welded and Tungsten Inert Gas Welded AA6061 T6 Aluminium Alloys
  • Author : Akshansh Mishra
  • Publisher : GRIN Verlag
  • Release : 2017-09-11
  • ISBN : 9783668521636
  • Language : En, Es, Fr & De
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Project Report from the year 2017 in the subject Engineering - Mechanical Engineering, grade: 8.9, SRM University, language: English, abstract: This paper deals with the mechanical, microstructural and fatigue analysis of welded joints. In the study, 6061-T6 aluminium alloy plates in 4mm thickness, that are particularly used for aerospace and in automotive industries, were welded using Tungsten Inert Gas (TIG) welding and Friction Stir Welding (FSW) methods as similar joints with one side pass and parameters of varying tool rotation, weld speed and 2.3 degree tool tilt angle. The weld zones cross sections were analysed with light optical microscopy (LOM). During recent years several investigations have been made of fatigue properties of friction stir welded joints. The great majority of available data from the fatigue analysis of friction stir welded joints are concerned with uniaxial loading conditions for a simple geometry. In uniaxial loading nominal stress is normally used as reference stress and it is easy to determine. However, fatigue failure is a highly localized phenomenon in engineering components and determining the nominal stress is not always possible due to the complexity of structures and presence of stress concentrators such as notches and cracks in which many approaches based on local parameters.