Pierluigi Fanelli1

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Experimental and numerical characterization of Friction Stir Spot Welded joints

Pierluigi Fanelli, Francesco Vivio , Vincenzo VulloUniversity of Rome Tor Vergata, Department of Mechanical Engineering, Via del Politecnico 1, 00133 Rome, Italy

a r t i c l e i n f o

Keywords:Friction Stir Spot WeldsFSSWFEMHAZTMAZ

a b s t r a c t

In this work, an analysis of a joint connected by Friction Stir Spot Welds (FSSW) is per-formed from both a numerical and an experimental point of view. The focus is to evaluatewhich structural parameters are strictly relevant to FSSW modeling in FE. Their determina-tion is of great importance for the elaboration of a new numerical model of a joint combin-ing efciency, accuracy in results and fast calculation. To this purpose, the FSSW joint isanalyzed by means of a complex 3D FE model which allows to evaluate, in a parametricmanner, the multifaceted internal geometry of the joint and the distribution of materialmechanical characteristics after welding. It is possible to evaluate the structural behaviorof the joint when new structural characteristics of the joint have been veried after thewelding process.

2011 Elsevier Ltd. All rights reserved.

1. Introduction

Arising problems in realizing welded joints from sheets of different materials that are difcult to obtain by employingcommonly used technologies, lead to a widespread use of new techniques of welding. Industrial interests principally focuson Friction Stir Spot Weld (FSSW).

Friction Stir Spot Welding (FSSW) is a new process that has recently received considerable attention from the automotive,aerospace, in-white and other industries [1]. This new welding technique owes its origins to linear friction stir welding(FSW), which was elaborated in 1991 by TWI [24] and developed by Mazda Motor Corporation [5] and Kawasaki HeavyIndustries [6] . Both FSW and FSSW seem promisingly ecologic welding methods, enabling to reduce material waste andto avoid radiation and harmful gas emission usually associated with the fusion welding processes; such innovative tech-niques also allow to join the so-called un-weldable or hard-to-weld light alloys or advanced high-strength steels (AHSS)[7,8] , which are very common materials in automotive or aerospace industries, with over 90% in power saving and 40% in

equipment saving versus resistance welding (RW) or resistance spot welding (RSW) [5,6] .FSSW is a solid-state welding process in which a specially designed rotating cylindrical tool with varying end geometryand a probe pin is rst plunged into the upper sheet. When the rotating tool contacts the upper sheet, a downward force isapplied whereas a backing tool beneath the lower sheet supports this downward force. The downward force and the rota-tional speed are maintained for an appropriate time to generate frictional heat. Then, heated and softened material adjacentto the tool deforms plastically, and a solid-state bond is made between the surfaces of the upper and lower sheet. Finally, thetool is drawn out of the sheets and protruded pin leaves a characteristic exit hole in the middle of the joint.

Heat and plastic ow coming from tool rotation determine remarkable microstructural modications resulting in localmodication of material mechanical characteristics around the joint. More specically, moving from the periphery of the

0013-7944/$ - see front matter 2011 Elsevier Ltd. All rights reserved.doi: 10.1016/j.engfracmech.2011.07.009

Corresponding author.E-mail address: [email protected] (F. Vivio).

Engineering Fracture Mechanics 81 (2012) 1725

Contents lists available at ScienceDirect

Engineering Fracture Mechanics

j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / e n g f r a c m e c h
http://dx.doi.org/10.1016/j.engfracmech.2011.07.009mailto:[email protected]://dx.doi.org/10.1016/j.engfracmech.2011.07.009http://www.sciencedirect.com/science/journal/00137944http://www.elsevier.com/locate/engfracmechhttp://www.elsevier.com/locate/engfracmechhttp://www.sciencedirect.com/science/journal/00137944http://dx.doi.org/10.1016/j.engfracmech.2011.07.009mailto:[email protected]://dx.doi.org/10.1016/j.engfracmech.2011.07.009


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joint towards the nugget axis, i.e. towards the tool pin axis, rst of all the basic material (BM) is found, in which no metal-lurgical modication is found due to the welding process. Then there is a heat affected zone (HAZ), where the material hasundergone a thermal load that modied microstructure and mechanical properties. Further out, a thermo-mechanically af-fected zone (TMAZ) is found, in which the material was plastically deformed by the tool stirring action and an increase of thematerial average grain size is found. Finally, the nugget is found, i.e. the recrystallization area, in which original grains appearto be replaced with ne grains of uniform size showing nominal dimension of few l m [9,10] . However, it is nowadays tes-tied in many works in literature, that such material characterization, as demonstrated in these papers [9,10] are related tomechanical behavior and strength of joints obtained by FSSW. The analysis of reciprocal dependences between mechanicalstrength and microstructures leads to evaluate optimal parameters sets for the welding process. Main parameters are: toolgeometry, its rotational velocity, downward force applied to the tool and maintenance time of this force.

The fast expansion of the use of this welding technology has attracted attention and interest of many researchers, whohave analyzed several aspects, some of which inherent in the determination of optimal sets of process parameters, othersregarding microstructural characteristics of the joint, and lots more focussed on joint strength.

In particular, as concerns welding of light alloy sheets, Rodrigues et al. [11] studied the impact of welding parameters andgeometry of two different tools, one with a conical shoulder and the other with a at shoulder, on microstructure andmechanical characteristics (such as hardness prole, engineering stressstrain curves and formability) of joints. Tran et al.[12] , on the other hand, analyzed effects of maintenance time of tool on strength and failure modes of dissimilar spot frictionwelds between two different light aluminum alloy.

The mechanical behavior of aluminum spot friction welds under quasi-static loading conditions was studied in manyother papers [1317] . A comprehensive literature review for spot friction welds can be found in [18] . Most of the literatureis about spot friction welds between similar aluminumsheets. However, dissimilar spot friction welds between different alu-minum alloys sheets were investigated in [19,20] . Also in [21] this kind of welds was studied, in this case by both experi-ments and numerical simulations.

In order to obtain joints of light alloy with better mechanical characteristics, Buffa et al. [22] proposed a different oper-ational mode of the welding process, where the preloaded tool is characterized not only by a rotational motion around itsaxis, but also by an orbital motion following a variously-dened path, with the intent of providing a larger welding zone.In [23] the effect of tool geometry (concave, at and convex shoulder and cylindrical or triangular pin) on static strengthof aluminum joints has been studied, concluding that with a triangular pin it is possible to obtain, ceteris paribus , a doubledstatic strength compared to that obtainable with a cylindrical pin. Still on light alloys and not only with tensile-shear spec-imens but also with cross-tension ones, the effect of different pin lengths on microstructure, static strength and failure modeof joint has been analyzed. Lin et al. [24,25] estimated fatigue life of tensile shear specimens made in aluminum alloy 6-ser-ies, obtained with a concave shoulder [24] or a at shoulder [25] , using a crack propagation model based on stress intensityfactors, expressed both in terms of global loads and local stresses as function of kink length and kink angles experimentally

determined. This complex approach to the problem is exhaustively presented in many papers of the same authors.In paper [26] the fatigue life under cyclic loading conditions of FSSW joints on lap-shear specimens in aluminum 6061-T6are investigated. The investigation is similar to that explained in the previous two papers. With respect to the fatigue lifeassessment of other kind of welded joints, many work, such as Radaj [27] , Salvini et al. [28] on fatigue strength of spotwelded joints or Radai et al. [29] on fatigue strength of generic welded joints, can be taken as a reference for a new approachto dening fatigue life criteria for FSSW.

Other works such as [30] are similarly based on aluminum alloys in case of static loading, in which microstructures andfracture mechanisms are investigated, concluding that a fracture starts at the interface between HAZ and TMAZ, where a de-crease of mechanical characteristics evidently causes a softening phenomenon.

In paper [31] , which is based on fracture mechanisms under almost-static loads and cyclic ones, both with high and lownumber of cycles, joint fatigue behavior of tensile shear specimens with aluminum alloys series 5 and 6, obtained either by aat or a concave shoulder tool, is studied. Crack propagation model is based on structural stress that is analytically dened inclosed form similarly to criterions presented in [24,25] .

In paper [32] a feasibility study is proposed for application of FSSW process even to joints between two different high-strength steels; the rst one is DP 600, a dual-phase steel with ultimate tensile stress of 600 MPa, and the second one isM 190, a martensitic steel with ultimate tensile stress of 1310 MPa. On tensile shear specimens and cross-tension specimensobtained with two different maintenance time of tool, microstructural change is analyzed and hardness prole in axial sec-tion of joint is detected, in order to dene an optimized welding parameter set for each alloy. In [33] , mainly of metallurgicalinterest, correlations between process parameters (chiey pin penetration in sheets) and microstructural characteristics,fracture mode and static strength are studied, when FSSW is performed on tensile shear specimens in aluminum alloy of series 6.

Numerical approach to the FSSW analysis is restricted to forming process of joint and it is carried out with FEM explicitmodels. In this context, it is worth mentioning works [34,35] , where, through the modeling of tool and sheets portion nearthe nugget, temperature front and its propagation are dened and plastic deformations and stresses are analyzed. In partic-ular, in paper [34] the authors investigate the thermo-mechanical processes in the material (aluminum 2024 alloy) duringthe plunge phase using numerical simulation and experiments; the model consists of a rigid stir welding tool and a deform-

able work-piece, meshed using eight node-coupled temperature displacement brick elements. In the paper [35] , the authorpresent temperature and stress graphs in the radial direction as well as temperature-deformation plots in aluminum alloy

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6061-T6 work-piece; adaptive meshing, which uses the same previous brick elements and permits to maintain mesh qualityunder large deformations, is utilized to simulate the material ow and temperature distribution in FSSW process.

The use of FEA methods for the structural analysis of FSSW is still not widely used. Joint strength is mainly analyzed undera technological point of view, in order to dene a production optimum, whose validation is limited to experimentation.

In this paper, the foundations are laid of elaborating of a new FE model, with a reduced computational burden, and theability to simulate joint behavior. This approach is based on a particular element characterized by computational lightness,already assessed for other kind of joints in [36] , and accuracy aside from which the material has been chosen. However, toreach this goal, it is necessary to setup a complex numerical model of reference, in order to provide a comparison term indeveloping the new element.

In this paper, a rst set of results are presented for strength characterization of a FSSW joint. Experimental tests are con-ducted on tensile-shear specimens with a unique FSSW joint, made of aluminum 6082-T6 alloy and statically loaded.

Material characteristics, known in nominal conditions, have been obtained through micro-hardness tests on welded spec-imens. In this way it is possible to achieve a systematic investigation to evaluate welding parameters inuence on local var-iation of mechanical characteristics of material. Through these information, it is possible to dene in the reference FE modela differentiation of heat and thermo-mechanically affected zones, in order to accurately evaluate the resulting structuraleffects.

Experimental results elaboration provides an information database for the creation of a numerical model of high com-plexity, with a high number of parameters so that it is possible to faithfully simulate experimental tests in both geometricand technological terms.

Working on these parameters variability it is possible to evaluate every parameters inuence on joint behavior by com-paring FE results to experimental data.

2. Numerical model of reference

In order to realize a tool that allows to evaluate the structural behavior of a joint in the case of static loads, it is necessaryto dene a detailed, completely parametric numerical model, using FE methods. A high level of accuracy for the FE model isrequested for evaluating, also through experimental data matching, the impact of technological parameters on the stiffnessand strength of the structure. The technological welding process determines the joint geometry on one hand, and on theother hand it modies the mechanical characteristics of the material portion close to the joint. In FSSW the welding processcauses an extensive change of mechanical properties of the material in a differentiated way, depending on the distance fromthe center of the junction. Both characteristic dimensions of these affected zones and the extent of properties degradationare strictly connected to alloy composition of the material and to technological parameters of the process. It is evident how

the parametrisation of the FE model must be thorough in order to provide a good estimate of joint geometry, material char-acteristics and size of each heat affected zone.The denition of a correlation between dimensions of joint and of its zones with differentiated mechanical characteristics

and process parameters needs an appropriate calculus for forming process analysis; this investigation must be carried outusing FE explicit codes and it is a work in progress by the authors. However, in this rst paper, differentiated zones dimen-sions have been detected directly from experimental specimens, while zones shape has been assumed from literature [30] .

Numerical model of joint is meshed with 8-nodes solid elements having 3 degrees of freedom, while metal sheets close tothe junction are modeled with shell elements with 4 nodes and 6 degrees of freedom. The choice of using different elementsin 3D and 2D is due to the dual need for highly-detailed in simulation and for downsizing the computational burden.

In order to obtain a partition of material close to junction in zones with different mechanical properties, a mapped meshhas been generated for the weld section ( Fig. 1).

Fig. 1 shows the partition of welded joint in three parts, visible in the schematic representation of axial section of it.Sheets thicknesses t 1 and t 2 of base material (BM) are 1.5 mm, while t 0 is due to tool penetration and is 0.02 mm. BM zone

represents material that shows no modication in properties. The innermost zone, known as Stir Zone, located all around theblind hole generated by tool pin, presents a complete re-crystallization, as it is demonstrated experimentally in [37] , andassumes an irregular section with a contour similar to a semicircle. As you move along the radius direction towards externalradius, the material has been modied mechanically by the tool and thermically by the generated heat when the frictionbetween metal and tool occurs (TMAZ); also in this zone, where its external diameter denes the nugget, the material is syn-crystallized. Beyond this zone, the material is subjected exclusively to the effects of heat dissipated during the welding pro-cess; this zone also an axial symmetric one is called heat affected zone (HAZ). The outer material beyond this zone isconsidered not modied by the welding process (BM).

Therefore, the main geometric parameters of the model are the domain diameters of these three zones and the Stir Zoneprole; such parameters are strictly correlated to technological ones typical of welding process, such as rotational velocity of the tool, its dimensions, maintenance time in position of the tool and the downward load applied on the sheet.

Tool penetration depth and downward load, in addition to tool dimensions, determine the junction geometry, whosecharacteristic dimensions in the model are represented by mark depth of tool shoulder and pin, and their diameters. Another

important parameter is the diameter of the actual joined portion of sheets ( syncrystallized material), representative of the junction ( Fig. 1). All these geometric parameters are obtained directly from experimental specimens.

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Load and constraint sets of numerical model (shown with a detail of the joint core in Fig. 2) simulate tension test with anextremity completely clamped in all its degree of freedom, and on the other side, only translation in direction of specimenprincipal axis is permitted.

Numerical simulation is carried out considering the elasto-plastic behavior of the material; in fact, the interest is focusednot only on joint strength in case of elastic behavior up to arising of local plasticization, but also on a preliminary valuation of fracture modes to be compared to experimental analysis.

3. Experimental tests and numerical matching

Tensile shear specimens are carried out joining sheets in aluminum 6082 T6 alloy of dened geometry ( Fig. 3); this mate-rial has been previously characterized with tensile tests on standard specimens, through which the mechanical characteris-tics, reported in Table 1 , are obtained. Specimen dimensions are shown in Fig. 3; clamping depth is 50 mm.

Before carrying out a tension test of the specimens, they have been examined locally to determine the mechanical prop-erties of the material close to the joint. The micro-hardness FIMEC tests, whose characteristics are presented in [38] , effec-tuated progressively farther from weld center, show a trend of material hardness with variable slope. Against a remarkableand progressive decreasing of hardness from base material toward the weld center, especially in the heat affected zone, thereis a notable increasing of hardness when the Thermo Mechanical Zone begins. That is coherent to what is known in literaturedue to effects of the mechanical process on material characteristics and it is conrmed by the analysis of microstructure evo-lution of the material during the forming phase of the joint. Where material is subjected exclusively to heat treatment, graindimensions are not subjected to considerable variations, while the material changes its composition due to the formation of

precipitates, resulting in a reduction of hardness. Higher temperatures and mechanical pressures applied in the central zoneof the junction cause the re-crystallization of this part of material, without reaching the melting point, but causing its struc-

Fig. 1. Junction zones with different mechanical characteristics.

Fig. 2. Detail of FSSW joint section in reference FE model.



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ture to re-organize and forming smaller grains, although with an altered composition. Consequently, only the heat affectedzone presents an impressive degradation of mechanical characteristics of the material.

Although this variation of mechanical properties is to be considered with no solution of continuity, in order to dene theFE model an average value of characteristics for each zone ( Fig. 2) is applied, obtaining some discontinuity of properties atborder zones. This introduced approximation, however, is justied by the sharp variation of mechanical characteristics no-ticed experimentally, switching from base material to HAZ and from this to TMAZ. This sharp variation seems to be coherentto the particular procedure represented by FSSW technology. It should be noticed that from experimental test FIMEC no sub-stantial variation of the Young modulus is detected, as expected through literature evidences. What has been obtained fromFIMEC test has been introduced in the numerical model characterizing the three different zones in Fig. 2, according to thevalue shown in Table 2 .

Fig. 3. Geometric characteristics of tensile shear specimen with FSSW joint.

Table 1

Mechanical properties of base material of specimens.

Material E (MPa) Rs (MPa) Rm (MPa)Al 6082 T6 65,000 275 385

Table 2

Yield stress values.

Zone Rs (MPa)

BM 275HAZ 60TMAZ 140SZ 140

Fig. 4. Numerical results with uniform material on the junction.



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Once the model geometry is dened through experimental survey, it is necessary to determine the correct distribution of mechanical properties and the simulation methods of FE model. To this end, rstly the inuence of plastic behavior of mate-rial in terms of hardening curve is investigated. In Fig. 4 the curves load P displacement u x of the numerical model are pre-sented, where the material is considered with uniform characteristics in all the three zones of the joint. Displacement data

Fig. 5. Comparison between experimental and numerical results with uniform material and with differentiated material on three characteristic zones.

Fig. 6. Failure mode in tensile shear specimen with FSSW .

Fig. 7. Equivalent Von Mises plastic deformation contour on spot. Load P = 3600 N.



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are detected where the extensometer was applied in the experimental test. The extensometer was positioned at the extrem-ities of the overlapping zone of the sheets of tensile shear specimen (base distance 25 mm).

Fig. 8. Triaxiality factor and equivalent Von Mises plastic deformation contours on spot for various load levels (averaged element solutions).



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In terms of global stiffness, the junction behavior shows to be unrelated to the actual stress-natural strain curve, whetherit is a perfectly plastic behavior, a linear hardening or a not-linear hardening. In this last case, the stressstrain curve r e(eulerian or actual stress logarithmic or natural strain) is introduced with a split line and so with a multi-linear hardeninglaw. Thanks to the results obtained, in order to dene the model material without losing accuracy, a plastic behavior hasbeen introduced dening the stressstrain curve as a bilinear hardening. The bilinear law has been dened in each zoneby yield stresses, obtained with FIMEC tests, by the same Young modulus of base material (65 GPa) and by a constant slopeof hardening (500 MPa).

Subsequently, an investigation of the inuence of the variation of material characteristics is performed. In tensile shear FEmodel, an uniform material with unaffected properties is rstly introduced, followed by a differentiation of mechanical char-acteristics in the three zones with the values previously obtained from experimental tests. In all these material curves, abilinear hardening is used.

The presence of a material ring so mechanically degraded around the spot causes the joint strength to drop; a behaviorsimilar to the experimental one is obtained, as shown in Fig. 5. In this gure, the average values of experimental tests ontensile shear specimens are shown. The displacements displayed are still those measured by the extensometer.

Finally the strain evolution in the welded joint is analyzed numerically. Particularly, the plastic strain trend is evaluatedin the zone near the weld. The highest values of plastic strain show on the top sheet, in the HAZ in correspondence of thick-ness variation, in the border with TMAZ aligned to the load axis. This result, related to the fact that the model presents asharp variation of mechanical characteristics just in the HAZ, is coherent with experimental surveys, where all specimensconrm such behavior. In Fig. 6, it is clear that the failure mechanism starts just where the highest values of plastic strainare obtained in the numerical model, in the case of a FE model with material characteristics differentiated in the three zoneoutlined previously ( Fig. 7). It is also signicant to analyze the contours on joint zone of the triaxiality factor TF (ratio of hydrostatic stress to equivalent von Mises stress) and equivalent Von Mises plastic deformation, for various load levels(Fig. 8). It is known that the triaxiality of the stress state greatly inuences the amount of plastic strain which a materialmay undergo before ductile failure occurs; for the highest values of the applied load, the triaxiality factor behavior(Fig. 8) justies the observed failure mechanism. The investigation of some other kinds of FSSW joints and the analysis of their strain evaluation to failure and the evaluation of TF can be the basis for the denition of a static failure criterion of thiskind of joint.

In the analyzed case, it is obvious that, due to the high decrease in material properties in the HAZ, the failure mechanismhappens there ( / TMAZ/HAZ in Fig. 1) in pull-out mode, before the notch effect occurs between the sheets ( / nugget ).

4. Conclusions

In this work a structural analysis of elasto-plastic behavior of a welded joint with Friction Stir Spot Weld technology is

performed. The purpose is to dene the parameters that show a large inuence on correct simulation of its behavior, espe-cially in terms of local strength of the junction. This has been analyzed using a complex three-dimensional FE model thatallows to parametrically consider the differentiation of the internal geometry of the joint and the variability of the mechan-ical properties of the material, caused by the welding process. The variation of mechanical characteristics has been veriedexperimentally through local micro-hardness tests, and the resulting data have been implemented into the numerical modelof the joint. Consequently the FE model validation, by matching the numerical results with the experimental ones, allows toevaluate the main parameters that inuence the mechanical behavior and strength of the welded junction.

References

[1] Hancock R. Friction welding of aluminum cuts energy cost by 99%. Weld J 2004;83:40.[2] The Welding Institute (TWI), Thomas WM, Nicholas ED, Needham JC, Murch MG, Temple-Smith P, Dawes CJ. PCT world patent application WO 93/

10935. Publ; June 10, 1993.[3] The Welding Institute (TWI), Thomas WM, Nicholas ED, Needham JC, Temple-Smith P, Kallee WKW, Dawes CJ. UK patent application 2306366 A. Publ;

May 7, 1997.[4] The Welding Institute (TWI), Thomas WM, Murch MG, Nicholas ED, Needham JC, Temple-Smith P, Dawes CJ. European patent application 653265 A2.Publ; May 17, 1995.

[5] Sakano R, Murakami K, Yamashita K, Hyoe T, Fuzimoto M, Inuzuka M, et al. Development of spot FSW robot system for automotive body members. In:Proceedings of the 3rd international symposium of friction stir welding, Kobe, Japan, September 2728, 2001.

[6] Iwashita T. Method and apparatus for joining. US patent, 6601751 B2; August 5, 2003.[7] The Welding Institute (TWI), Shi SG, Westgate SA. Resistance spot welding of high-strength steel sheet. Corporate research program report, 767/2003;

2003.[8] Spinella DJ, Brockenbrough JR, Fridy JM. Trend in aluminum resistance spot welding for the automotive industry. Weld J 2005;84(1):3440.[9] Jata KV, Semiatin SL. Continuous dynamic recrystallization during friction stir welding of high strength aluminumalloys. Scripta Mater 2000;43:7439.

[10] Fratini L, Buffa G. CDRX modeling in friction stir welding of aluminum alloys. Int J Mach Tools Manuf 2005;45(10):118894.[11] Rodrigues DM, Loureiro A, Leitao C, Leal RM, Chaparro BM, Vilaa P. Inuence of friction stir welding parameters on the microstructural and

mechanical properties of AA 6016-T4 thin welds. Mater Des 2009;30:191321.[12] Tran VX, Pan J, Pan TE. Effects of processing time on strengths and failure modes of dissimilar spot friction welds between aluminum 5754-O and 7075-

T6 sheets. J Mater Process Technol 2009;209:372439.[13] Fujimoto M, Inuzuka M, Nishio M, Nakashima Y. Development of friction spot joining (Report 1) cross sectional structures of friction spot joints. Natl

Meet Jpn Weld Soc 2004;74:45.

[14] Fujimoto M, Inuzuka M, Nishio N, Nakashima Y. Development of friction spot joining (Report 2) mechanical properties of friction spot joints. NatlMeet Jpn Weld Soc 2004;74:67.



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[15] Hinrichs JF, Smith CB, Orsini BF, DeGeorge RJ, Smale BJ, Ruehl PC. Friction stir welding for the 21st century automotive industry. In: Proceedings of the5th international symposium of friction stir welding, Metz, France, September 1416, 2004.

[16] Lin PC, Lin SH, Pan J, Pan T, Nicholson JM, Garman MA. Microstructures and failure modes of spot friction welds in lap-shear specimens of aluminum6111-T4 sheets. SAE Technical Paper No. 2004-01-1330. Society of Automotive Engineers, Warrendale, PA; 2004.

[17] Pan T, Joaquin A, Wilkosz DE, Reatherford L, Nicholson JM. Spot friction welding for sheet aluminum joining. In: Proceedings of the 5th internationalsymposium of friction stir welding, Metz, France, September 1416, 2004. p. 7996.

[18] Pan T. Friction stir spot welding (FSSW) a literature review. SAE Technical Paper No. 2007-01-1702. Society of Automotive Engineers, Warrendale,PA; 2004.

[19] Tozaki Y, Uematsu Y, Tokaji K. Effect of processing parameters on static strength of dissimilar friction stir spot welds between different aluminiumalloys. Fatigue Fract Engng Mater Struct 2007;30:1438.

[20] Tweedy BM, Widener CA, Merry JD, Brown JM, Burford DA. Factors affecting the properties of swept friction stir spot welds, SAE Technical Paper No.2008-01-1135. Society of Automotive Engineers, Warrendale, PA; 2008.

[21] Su P, Gerlich A, North TH, Bendzsak GJ. Intermixing in dissimilar friction stir spot welds. Metall Mater Trans 2007;A 38A:58495.[22] Buffa G, Fratini L, Piacentini M. On the inuence of tool path in friction stir spot welding of aluminum alloys. J Mater Process Technol

2008;208:30917.[23] Badarinarayan H, Shi Y, Li X, Okamoto K. Effect of tool geometry on hook formation and static strength of friction stir spot welded aluminum 5754-O

sheets. Int J Mach Tools Manuf 2009;49:81423.[24] Lin PC, Pan J, Pan T. Failure modes and fatigue life estimations of spot friction welds in lap-shear specimens of aluminum 6111-T4 sheets. Part 1: Welds

made by a concave tool. Int J Fatigue 2008;30:7489.[25] Lin PC, Pan J, Pan T. Failure modes and fatigue life estimations of spot friction welds in lap-shear specimens of aluminum 6111-T4 sheets. Part 2: Welds

made by a at tool. Int J Fatigue 2008;30:90105.[26] Wang DA, Chen CH. Fatigue lives of friction stir spot welds in aluminum 6061-T6 sheets. J Mater Process Technol 2009;209:36775.[27] Radaj D. Structural stress, notch stress and stress intensity factor approach for assessment of fatigue strength of spot welded joints. Weld World

1990;28:2939.[28] Salvini P, Vivio F, Vullo V. Fatigue life assessment for multi-spot welded structures. Int J Fatigue 2009;31:1229.[29] Radaj D, Berto F, Lazzarin P. Local fatigue strength parameters for welded joints based on strain energy density with inclusion of small-size notches.

Engng Fract Mech 2009;76:110930.[30] Wang DA, Lee SC. Microstructures and failure mechanisms of friction stir spot welds of aluminum 6061-T6 sheets. J Mater Process Technol

2007;186:2917.[31] Tran VX, Pan J, Pan T. Fatigue behavior of aluminum 5754-O and 6111-T4 spot friction welds in lap-shear specimens. Int J Fatigue 2008;30:217590.[32] Feng Z, Santella ML, David SA, Steel RJ, Packer SM, Pan T, et al. Friction stir spot welding of advanced high-strength steels a feasibility study. SAE Int

2005;01:1248.[33] Mitlin D, Radmilovic V, Pan T, Chen J, Feng Z, Santella ML. Structureproperties relations in spot friction welded (also known as friction stir spot

welded) 6111 aluminum. Mater Sci Engng 2006;A 441:7996.[34] Mandal S, Rice J, Elmustafa AA. Experimental and numerical investigation of the plunge stage in friction stir welding. J Mater Process Technol

2008;203:4119.[35] Awang M, Mucino VH, Feng Z, David SA. Thermo-mechanical modeling of friction stir spot welding (FSSW)process: use of an explicit adaptive meshing

scheme. SAE Int 2005;01:1251.[36] Vivio F. A new theoretical approach for structural modelling of riveted and spot welded multi-spot structures. Int J Solids Struct 2009;46(22/

23):400624.[37] Fanelli P, Montanari R, Rovatti L, Ucciardello N, Vivio F, Vullo V. Caratterizzazione microstrutturale e modellazione di giunti saldati per Friction Stir

Spot Welding in lega 6082 2010, 33 Convegno Nazionale AIM.[38] Riccardi B, Montanari R, Moreschi LF, Sili A, Storai S. Mechanical characterisation of fusion materials by indentation test. Fusion Engng Des 2001;58

59:7559.


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