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Viewing 1 to 15 of 15
2013-04-08
Journal Article
2013-01-1023
Seung Hoon Hong, Katherine Avery, Jwo Pan, Michael Santella, Zhili Feng, Tsung-Yu Pan
Failure mode and fatigue behavior of friction stir spot welds made with convex and concave tools in lap-shear specimens of dissimilar high strength dual phase steel (DP780GA) and hot stamped boron steel (HSBS) sheets are investigated based on experiments and a kinked fatigue crack growth model. Lap-shear specimens with the welds were tested under both quasistatic and cyclic loading conditions. Optical micrographs indicate that under both quasi-static and cyclic loading conditions, the welds mainly fail from cracks growing through the upper DP780GA sheets where the tools were plunged in during the welding processes. Based on the observed failure mode, a kinked fatigue crack growth model is adopted to estimate fatigue lives of the welds. In the kinked crack fatigue crack growth model, the stress intensity factor solutions for fatigue life estimations are based on the closed-form solutions for idealized spot welds in lap-shear specimens.
2013-04-08
Journal Article
2013-01-1020
Wei-Jen Lai, Jwo Pan, Zhili Feng, Michael Santella, Tsung-Yu Pan
Failure modes and fatigue behaviors of ultrasonic spot welds in lap-shear specimens of magnesium AZ31B-H24 and hot-dipped-galvanized mild steel sheets with and without adhesive are investigated. Ultrasonic spot welded, adhesive-bonded, and weld-bonded lap-shear specimens were made. These lap-shear specimens were tested under quasi-static and cyclic loading conditions. The ultrasonic spot weld appears not to provide extra strength to the weld-bonded lap-shear specimen under quasi-static and cyclic loading conditions. The quasi-static and fatigue strengths of adhesive-bonded and weld-bonded lap-shear specimens appear to be the same. For the ultrasonic spot welded lap-shear specimens, the optical micrographs indicate that failure mode changes from the partial nugget pullout mode under quasi-static and low-cycle loading conditions to the kinked crack growth mode under high-cycle loading conditions.
2013-04-08
Journal Article
2013-01-1017
Tsung-Yu Pan, Zhili Feng, Michael Santella, Jian Chen
Development of reliable magnesium (Mg) to steel joining methods is one of the critical issues in broader applications of Mg in automotive body construction. Ultrasonic spot welding (USW) has been demonstrated successfully to join Mg to steel and to achieve strong joints. In this study, corrosion test of ultrasonic spot welds between 1.6 mm thick Mg AZ31B-H24 and 0.8 mm thick galvanized mild steel, without and with adhesive, was conducted. Adhesive used was a one-component, heat-cured epoxy material, and was applied between overlapped sheets before USW. Corrosion test was conducted with an automotive cyclic corrosion test, which includes cyclic exposures of dipping in the 0.5% sodium chloride (NaCl) bath, a constant humidity environment, and a drying period. Lap shear strength of the joints decreased with the cycles of corrosion exposure. Good joint strengths were retained at the end of 30-cycle test.
2012-04-16
Journal Article
2012-01-0479
Seung-Hoon Hong, Kulthida Sripichai, Chia-Siung Yu, Katherine Avery, Jwo Pan, Tsung-Yu Pan, Michael Santella
Failure modes of friction stir spot welds in lap-shear specimens of dissimilar high strength dual phase steel (DP780GA) and hot stamped boron steel (HSBS) sheets are investigated under quasi-static and cyclic loading conditions based on experimental observations. Optical micrographs of dissimilar DP780GA/HSBS friction stir spot welds made by a concave tool before and after failure are examined. The micrographs indicate that the failure modes of the welds under quasi-static and cyclic loading conditions are quite similar. The micrographs show that the DP780GA/HSBS welds mainly fail from cracks growing through the upper DP780GA sheets where the concave tool was plunged into during the welding process. Based on the observed failure modes, a kinked fatigue crack growth model is adopted to estimate fatigue lives.
2012-04-16
Technical Paper
2012-01-0472
Tsung-Yu Pan, Michael Santella
Development of reliable magnesium (Mg) to steel joining methods is one of the critical issues in boarder applications of Mg in automotive body construction. However, due to the large difference of melting temperatures of Mg and steel, fusion welding between two metals is very challenging. Ultrasonic spot welding (USW) has been demonstrated to join Mg to steel without melting and to achieve strong joints. However, galvanic corrosion between Mg and steel is inevitable but not well quantified. In this study, corrosion test of ultrasonic spot welds between 1.6-mm-thick Mg AZ31B-H24 and 0.8-mm-thick galvanized mild steel was conducted. No specific corrosion protection was applied in order to study the worst corrosion behavior. Corrosion test was conducted with an automotive cyclic corrosion test, which includes cyclic exposures of dipping in the salt bath, air drying, then a constant humidity environment. Lap shear strength of the joints decreased linearly with the cycles.
2012-04-16
Technical Paper
2012-01-0474
Tsung-Yu Pan, Michael Santella
Ultrasonic spot welding (USW) is a promising joining method for magnesium to steel to overcome the difficulties of fusion welding for these two materials with significant differences in melting temperatures. In a previous paper, the results of ultrasonic spot welding of magnesium to steel, with sonotrode engaged Mg piece, was presented. In this study, same material combination (0.8-mm-thick galvanized mild steel and 1.6-mm Mg AZ31B-H24) was used, but with sonotrode engaging steel piece. Various welding time, from 0.4 to 2.0 sec, were applied. Tensile lap-shear test, optical metallography, and scanning electron micrography were conducted for joint strength measurement and microstructural evaluation. The joint strength reached over 4.2 kN at 1.8 sec welding time. Mg-Zn eutectic was formed at the interface, indicating the interfacial temperature over 344°C. The study demonstrated USW to be a viable process for potential manufacturing of mixed-metal joints.
2008-04-14
Technical Paper
2008-01-1139
Van-Xuan Tran, Jwo Pan, Tsung-Yu Pan
Fatigue behaviors of aluminum 5754-O spot friction welds made by a concave tool in lap-shear specimens are investigated based on experimental observations and a fatigue life estimation model. Optical micrographs of the welds before and after failure under quasi-static and cyclic loading conditions are examined. The micrographs indicate that the failure modes of the 5754 spot friction welds under quasi-static and cyclic loading conditions are quite different. The dominant kinked fatigue cracks for the final failures of the welds under cyclic loading conditions are identified. Based on the experimental observations of the paths of the dominant kinked fatigue cracks, a fatigue life estimation model based on the stress intensity factor solutions for finite kinked cracks is adopted to estimate the fatigue lives of the welds.
2008-04-14
Technical Paper
2008-01-1138
Van-Xuan Tran, Jwo Pan, Tsung-Yu Pan
Abstract In this investigation, dissimilar 5754/7075 and 7075/5754 spot friction welds were first made under different processing conditions. The spot friction welds in lap-shear specimens were tested under quasi-static loading conditions. The optimal processing times to maximize the failure loads of the 5754/7075 and 7075/5754 welds under lap-shear loading conditions are identified. The maximum failure load of the 7075/5754 welds is about 40% larger than that of the 5754/7075 welds. Optical micrographs of both types of spot friction welds made at different processing times before and after failure are examined. The micrographs show different weld geometries and different failure modes of spot friction welds made at different processing times. The failure modes of the 5754/7075 and 7075/5754 spot friction welds appear to be quite complex and strongly depend on the geometry and the strength of the interfacial surface between the two deformed sheet materials.
2009-04-20
Journal Article
2009-01-0023
Tsung-Yu Pan, Michael L. Santella, Nic Blundell
The Friction Stir Spot Welding (FSSW) process is a derivative of the friction stir welding (FSW) process, without lateral movement of the tool during the welding process. It has been applied in the production of aluminum joining for various Mazda and Toyota vehicles. Most of the applications and published studies were concentrated in aluminum sheet in the range of 1.0 to 1.5 mm, suitable for non-structural automotive closure applications. The objective of this study is to study the feasibility of FSSW process for automotive structural aluminum joining, up to 3 mm in thickness, for potentially replacement of self-piercing rivets (SPR) process. Joining thicker aluminum with FSSW tooling with a typical smooth concave shoulder and threaded probing pin, requires long process time, which would not be appropriate in mass-production automotive body construction. In this paper, an innovative FSSW tool with grooved shoulder was developed.
2007-04-16
Technical Paper
2007-01-1702
Tsung-Yu Pan
The Friction Stir Spot Welding (FSSW) process is a derivative of the friction stir welding (FSW) process, without lateral movement of the tool during the welding process. It has been used in the production of aluminum doors, engine hoods, and decklids in the Japanese automotive industry. It has the benefits of operation and investment cost savings, weight reduction, high repeatability and consistence, low maintenance, better work environment and recycleability vs. other aluminum spot joining methods such as resistance spot welding (RSW) and riveting. This paper provides a comprehensive literature review of the technology, including joining mechanisms, process controls, process parameter development, fracture behaviors, metallurgy, temperature, tool geometry, and material flow. Variations of the process, joining of aluminum to steel, steel to steel, magnesium, weldbonding (with adhesive), process simulation, and industrial applications are also discussed.
2004-03-08
Technical Paper
2004-01-0467
Ciro A. Soto, Tsung-Yu Pan
The use of structural foam in the automotive industry is gaining more acceptance for lighter and stronger body construction. However, its use requires new approaches in order to obtain optimal configurations. Along this line, a computer procedure to optimally design the topology of structural foams under crash loads is presented. The procedure is applied to a front rail subject to frontal crash as a demonstration of the technology. It is concluded that this procedure is a viable approach that enable design engineers to reduce the design time, and weight of new structural foam components.
2011-04-12
Journal Article
2011-01-0475
Teresa J. Franklin, Jwo Pan, Michael Santella, Tsung-Yu Pan
Fatigue behavior of dissimilar ultrasonic spot welds in lap-shear specimens of magnesium AZ31B-H24 and hot-dipped-galvanized mild steel sheets is investigated based on experimental observations, closed-form stress intensity factor solutions, and a fatigue life estimation model. Fatigue tests were conducted under different load ranges with two load ratios of 0.1 and 0.2. Optical micrographs of the welds after the tests were examined to understand the failure modes of the welds. The micrographs show that the welds mainly fail from kinked fatigue cracks growing through the magnesium sheets. The optical micrographs also indicate that failure mode changes from the partial nugget pullout mode under low-cycle loading conditions to the transverse crack growth mode under high-cycle loading conditions. The closed-form stress intensity factor solutions at the critical locations of the welds are used to explain the locations of fatigue crack initiation and growth.
2001-10-16
Technical Paper
2001-01-3080
Tsung-Yu Pan, Howard D. Blair, John M. Nicholson, Alan E. Gickler
Lead (Pb) based solders had been used successfully as dent and seam fillers for automotive body panels and were commonly referred to as “body solders”. The usual compositions were 70wt% Pb - 30wt% Sn or 80wt% Pb - 20wt% Sn. But due to the hazards associated with Pb dust and particles from the grinding and sanding, new lead-free body solders were developed in the early 80's. An 82wt%Sn - 15wt%Cu - 3wt%Zn composition was developed to mimic the pasty characteristics and processability of the lead-containing solders. This body solder has the advantages of corrosion resistance, compatibility with e-coat, and a lower processing temperature and lower material cost than an alternative candidate approach that uses a silicon bronze material. The ideal temperature range for applying this solder is between 280 to 350°C, which provides a workable, viscous material.
2010-04-12
Journal Article
2010-01-0961
Van-Xuan Tran, Jwo Pan, Tsung-Yu Pan
Fatigue behavior of spot friction welds or friction stir spot welds in lap-shear specimens of dissimilar aluminum 5754-O and 7075-T6 sheets is investigated based on experimental observations and two fatigue life estimation models. Optical micrographs of the 5754/7075 and 7075/5754 welds after failure under cyclic loading conditions are examined to understand the failure mechanisms of the welds. The micrographs show that the 5754/7075 welds mainly fail from the kinked fatigue crack through the lower sheet thickness. Also, the micrographs show that the 7075/5754 welds mainly fail from the kinked fatigue crack through the lower sheet thickness and from the fracture surface through the upper sheet thickness.
2010-04-12
Journal Article
2010-01-0975
Michael Santella, Teresa J. Franklin, Jwo Pan, Tsung-Yu Pan, Elliot Brown
Ultrasonic spot welds were made between sheets of 0.8-mm-thick hot-dip-galvanized mild steel and 1.6-mm-thick AZ31B-H24. Lap-shear strengths of 3.0-4.2 kN were achieved with weld times of 0.3-1.2 s. Failure to achieve strong bonding of joints where the Zn coating was removed from the steel surface indicate that Zn is essential to the bonding mechanism. Microstructure characterization and microchemical analysis indicated temperatures at the AZ31-steel interfaces reached at least 344°C in less than 0.3 s. The elevated temperature conditions promoted annealing of the AZ31-H24 metal and chemical reactions between it and the Zn coating.
Viewing 1 to 15 of 15

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