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Journal Article

Development of Friction Stir Clinching Process for Alclad 2024-T3 Aluminum Sheets

2016-04-05
2016-01-0505
A concept of combining friction stir spot welding (FSSW) and clinching, denoted as friction stir clinching (FSC), was proposed to join alclad 2024-T3 aluminum sheets. A tool, having a smooth probe and a flat shoulder, and a die, having a circular cavity and a round groove, were used to make FSC joints. The failure loads and fatigue lives of FSC joints made by various punching depths, rotational speeds, and dwelling times, were evaluated to obtain the admissible processing parameters. Optical micrographs of the FSC joints, before and after failure, were examined to understand the effects of processing parameters on the mechanical interlock and alclad layer distribution, which strongly correlate to the failure load, failure mode, and fatigue life of FSC joints. Finally, the static and fatigue performance of FSC joints made by the admissible processing parameters was obtained. The feasibility of the FSC process for alclad 2024-T3 aluminum sheets was confirmed.
Journal Article

Failure Mode and Fatigue Behavior of Dissimilar Laser Welds in Lap-Shear Specimens of Low Carbon Steel and HSLA Steel Sheets

2015-04-14
2015-01-0706
In this paper, failure modes of dissimilar laser welds in lap-shear specimens of low carbon steel and high strength low alloy (HSLA) steel sheets are investigated based on experimental observations. Micro-hardness tests across the weld zones of dissimilar laser welds were conducted. The hardness values of the fusion zones and heat affected zones are significantly higher than those of the base metals. The fatigue lives and the corresponding failure modes of laser welds as functions of the load ranges are then examined. Optical micrographs of the laser welds before and after failure under quasi-static and cyclic loading conditions are then examined. The failure modes and fatigue behaviors of the laser welds under different loading conditions are different. Under quasi-static loading conditions, a necking failure occurred in the upper low carbon steel sheet far away from the laser weld.
Journal Article

Fatigue Analysis of Swept Friction Stir Clinch Joints between Aluminum and Steel Sheets

2017-03-28
2017-01-0478
Fatigue analysis of swept friction stir clinch (Swept-FSC) joints between 6061-T6 aluminum (Al) and S45C steel (Fe) sheets was conducted through experimental approaches. Before fatigue tests, a parametric study for the probe geometry of FSC tools was conducted in order to eliminate the hook structure inside the joint and improve the mechanical performance of the joint. Then a series of quasi-static and fatigue tests for Al/Fe Swept-FSC joints in lap-shear (LP) and cross-tension (CT) specimens were conducted. The fatigue data were recorded. The fatigue behavior of Al/Fe Swept-FSC joints in LP and CT specimens were examined through optical and scanning electron microscopes. Experimental results indicated that LP specimens have two failure modes, while CT specimens have only one failure mode. The dominant fatigue crack of each failure mode was identified.
Journal Article

Fatigue Behavior of Self-Piercing Rivets and Clinch Joints in Lap-Shear Specimens of Aluminum Sheets

2013-04-08
2013-01-1024
Fatigue behavior of self-piercing rivets (SPRs) and clinch joints in lap-shear specimens of 6111-T4 aluminum sheets is investigated based on experimental observations and a fatigue life estimation model. Lap-shear specimens with SRPs and clinch joints were tested under cyclic loading conditions. Under cyclic loading conditions, fatigue cracks start from the curved interfacial surface of the upper sheet and then grow into the upper sheet thickness for both self-piercing rivets and clinch joints. The self-piercing rivets and clinch joints fail finally through the circumferential/transverse crack growth in the upper sheets and inner button crack growth, respectively. The structural stress solution and the experimental stress-life data for aluminum 6111-T4 sheets are adopted to estimate the fatigue lives of both types of joints. The fatigue life estimations based on the structural stress model show good agreement with the experimental results.
Journal Article

Fatigue Behavior of Spot Friction Welds in Cross-Tension Specimens of Aluminum 6061-T6 Sheets

2011-04-12
2011-01-0470
Failure modes of spot friction welds in cross-tension specimens of aluminum 6061-T6 sheets are first investigated based on experimental observations. Optical and scanning electron micrographs of the welds before and after failure under quasi-static and cyclic loading conditions are examined. Experimental results show that the failure modes of the welds under quasi-static and cyclic loading conditions are quite different. Under quasi-static loading conditions, the failure mainly starts from the necking of the upper sheet outside the weld. Under low-cycle loading conditions, the dominant fatigue cracks are the kinked cracks growing into the upper sheet from the crack tips; hence, the upper nugget pullout failure mode can be seen. Under high-cycle loading conditions, the dominant fatigue cracks are kinked cracks growing into the lower sheet from the crack tips; subsequently, the lower nugget pullout failure mode can be seen.
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