Lap-shear Load Research Articles

분리형 섕크를 갖는 SPR의 형상 설계를 위한 유한요소해석

SPR(Self-Piercing rivet) is mechanical element of joining sheet metal components without the need for pre-punched or pre-drilled holes. Newly designed SPR is developed for high joining strength and shearing strength than semi-tubular rivet. In this study, divided shank of self-piercing rivet were designed for joining DP440 and SILAFONT. Newly designed SPR was simulated by using FEM code DEFORM-3D. In simulations of SPR process, various shape of self-piercing rivet were considered for semi-tubular and newly designed SPR. In other to examine the joinability, joining load and lap-shear load of newly designed SPR were compared with semi-tubular by simulated results and experimental ones.

Effect of Rotational Speed on Microstructure and Mechanical Properties of Refill Friction Stir Spot Welded 2024 Al Alloy

Refill friction stir spot welding (RFSSW) was successfully used to weld alclad 2024 aluminum alloy with different thicknesses. Effects of tool rotational speed on the weld formation, microstructure, and mechanical properties of the RFSSW welds were mainly discussed. Results show that keyhole is successfully refilled and welding defects such as flash, annular groove, and material adhesion can be observed. A bright contrast bonding ligament is found embedded in the weld and it is thicker in the center. Defects of hook, void, lack of mixing, and incomplete refilling can be found at the thermo-mechanically affected zone/stir zone (TMAZ/SZ) interface, which can be attributed to weak metallurgical bonding effect. With increasing the tool rotational speed, thickness of the bonding ligament decreases, grains in the SZ coarsen, hardness of the SZ decreases, and lap shear load of the welds decreases. When changing the rotating speed, impact strength shows rather complicated variation trend.

Adhesive joining of copper using nano-filler composite adhesive

Effect of well dispersed nano particles filled epoxy based adhesive prepared by an innovative ultrasonic dual mixing on lap joint of copper was investigated. Effect of mechanical and chemical treatment of copper substrate on lap shear strength of its adhesive joint produced by using composite adhesive containing 5, 10, and 15 wt.% TiO2 particles of size 30 ± 5 nm. The lap shear strength of the joint was also studied as a function of bond line thickness of the adhesive. Fracture behavior of the joint under the lap shear loading has also been studied. Characteristics of the nano particles filled epoxy adhesive joints were compared with the adhesive joints of neat epoxy. Adhesive joint of chemically treated copper shows relatively higher lap shear strength than that of the mechanically treated copper while the joint of composite adhesive shows considerably higher strength as compared to that of the neat adhesive.

Influence of bonding technique on bond behavior of CFRP-to-clay brick masonry joints: Experimental study using particle image velocimetry (PIV)

This paper presents a comparative study on the performance of three different techniques for bonding carbon fiber reinforced polymer (CFRP) sheets to masonry substrate. To do so, eight CFRP-to-clay brick masonry joints were prepared using conventional externally bonded reinforcement (EBR) technique, with and without surface preparation. Moreover, for the first time, grooving method (GM) in the form of externally bonded reinforcement on grooves (EBROG) technique was used for bonding CFRP sheets to masonry substrate in six other joints. The specimens were tested under single lap-shear loading and the influence of bonding technique as well as effect of fiber reinforced polymer (FRP) bond length were comprehensively investigated and discussed based on the experimental results. A non-contact full field deformation measurement technique, i.e. particle image velocimetry (PIV), was used to obtain the load–slip diagrams, strain profiles along the bonded length, and strain fields of all tested specimens. Experimental results and PIV measurements demonstrated that bond behavior of CFRP sheets attached to masonry substrate was significantly improved by using EBROG technique. Consequently, the technique can be used as an alternative to conventional EBR method to more efficiently utilize the tensile capacity of FRPs used for external strengthening of unreinforced masonry (URM) structures.

Taguchi Optimization of Process Parameters in Friction Stir Spot Welding of AA5754 and AA2024 Alloys

The feasibility of friction stir spot welding was studied on AA5754-H22 and AA2024-T3 aluminum alloys which have widespread applications in aircraft and automotive industries. The quality of the joint was evaluated by examining the characteristics of the joint as a result of lap-shear fracture load. Taguchi approach of the parameter design was used as a statistical design of experiment technique to set the optimal welding parameters. The experiments were arranged by using Taguchi’s L9 orthogonal array. The signal-to-noise ratio and the analysis of variance were utilized to obtain the influence of the friction stir spot welding parameters on the lap-shear fracture load. Finally, the results were confirmed by further experiments.

Microstructure evolution and mechanical properties of Cu–Al joints by ultrasonic welding

Dissimilar joints of copper to aluminium were produced by high power ultrasonic welding (USW). The interfacial reaction between copper and 6061 aluminium alloy as a function of welding time was studied. The intermetallic compound (IMC) layer is mainly composed of CuAl2 and Cu9Al4. The thickness of the IMC layer increases with the welding time. For a relatively long welding time (0·7 s) in USW, the dendritic solidification microstructure was observed in local regions, owing to the occurrence of the eutectic reaction, α-Al+θ→L, in the welding process. The lap shear load (or strength) of the joints first increases and then decreases with increasing welding time, and the failure of the joints occurred dominantly at the interface. This is mainly attributed to the development of IMC layer at the interface.

Glass/epoxy composites and aluminium alloy joint using Kevlar® intermediate layer and nanoclay-reinforced epoxy adhesive

Adhesive lap joint between glass fibre/epoxy composites and aluminium alloy (2014 T4) was prepared by an in situ moulding process using a matched die mould. The surface of aluminium alloy was treated with chromic acid before adhesive bonding. Lap shear strength and fatigue life were evaluated in tensile mode and tension–compression mode (at 40% of lap shear load of adhesive joint), respectively. Knurling on the surface of aluminium alloy improved the lap shear strength of the adhesive joint but did not influence the fatigue life of the same. Lap shear strength and fatigue life of adhesive joint made with neat epoxy adhesive and reinforcement of an intermediate layer of Kevlar® between glass/epoxy composite and aluminium alloy were observed to be 0.44 kg/mm2 and 3.6 × 105 cycles, respectively. In another case, lap shear strength and fatigue life of similar type of adhesive joint made from nanoclay (Cloisite 30B)-reinforced epoxy adhesive and without reinforcement of an intermediate layer of Kevlar® were observed to be 0.38 kg/mm2 and 2.3 × 105 cycles, respectively. Whereas, lap shear strength and fatigue life of adhesive joint made from nanoclay-reinforced epoxy adhesive along with the reinforcement of an intermediate layer of Kevlar® were 0.48 kg/mm2 and 3.9 × 105 cycles, respectively. Therefore, adhesive joint made from nanoclay-reinforced epoxy adhesive along with the reinforcement of an intermediate layer of Kevlar® was the best.

Friction stir spot welded joints of 409L stainless steels fabricated by a convex shoulder tool

Spot joints of ferritic 409L stainless steel are successfully fabricated by friction stir spot welding (FSSW) using a convex shoulder tool. The welding process, microstructure and failure of the FSSW joint are investigated experimentally. During the FSSW process, the Z-force history shows significant variations depending on the contact phenomena between the tool and the joined sheets, while the Z-torque history shows a rather steady increase without pronounced changes in the trend until the initiation of dwelling. Electron back-scatter diffraction suggests that both continuous dynamic recrystallization and recovery occurred in the stir zone during the FSSW process. Observation of the FSSW joint that failed under the given lap shear load shows that the cracks, which are the result of the interfaces between the upper and lower sheets, propagated into the weld along the interfacial surfaces, after which a necking/shear failure occurred. Finally, the rupture of the joint, which was initiated by the necking/shear failure, propagated along the circumference of the weld.

Design of shot nailed steel sheeting connection at ambient and elevated temperatures

Shot nailed connections are widely used in roof constructions to fasten cold-formed steel sheeting to supporting trusses. At ambient temperatures, neither EN 1993-1-8 nor EN 1993-1-3 can be used directly for this type of connection. Besides, no design guidelines are available in EN 1993-1-2 for designing the same type of connection in fire. In this paper, with the verified Finite Element (FE) models and procedures, three major failure modes under lap shear loads, such as bearing failure, shear-out failure and net-section failure, are investigated. In addition, the material bearing failures, the effects from out-of-plane curling of thin sheet and the contribution from frictions between the connected parts are analyzed at both ambient and elevated temperatures. Further, parametric analyses are conducted to investigate the effects of the end distance, the edge distance and the protuberance height on the connection resistance. After that, the design resistance functions for bolted connections given in EN 1993-1-8 are revised for designing shot nailed connections. Finally, the design resistance functions are calibrated using First Order Reliability Method (FORM) and the partial safety factor is derived.

Effect of tool design and process parameters on properties of Al alloy 6016 friction stir spot welds

Friction stir spot welding (FSSW) of Al alloy 6016-T4 sheet was evaluated using a conventional pin (CP) tool and off-center feature (OC) tool. Tool rotation speed and plunge depth were varied to determine the effect of individual process parameter on lap-shear separation load. Maximum separation load of about 3.3kN was obtained by using a 0.2mm shoulder penetration depth with 1500rpm tool rotation speed for the CP tool and 2500rpm for the OC tool. Three different weld separation modes under lap-shear loading were observed: interfacial separation, nugget fracture separation and upper sheet fracture separation. Microhardness profile for weld cross section indicated no direct relationship between microhardness distribution and separation locations.

Mechanical characterization of friction stir spot microwelds

Microstructures and failure mechanisms of friction stir spot microwelds in 300-μm thin sheet of aluminum 1050 alloy were investigated. As an alternative to conventional soldering and welding in joining thin metals for electronic, medical and microdevices, friction stir welding may be utilized in order to limit the excessive heat damage. Transmission electron microscopy micrographs of the cross sections of friction stir spot microwelds in lap-shear specimens were examined. These microwelds showed the failure mode of nugget pullout under lap-shear loading conditions. The experimental observations suggested that under lap-shear loading conditions, the failure was initiated near the possible original notch tip in the stir zone and the failure propagated along the circumference of the nugget to final fracture. Microindentation hardness data of base metal, heat affected zone, thermal-mechanical affected zone and stir zone were obtained. The interface between the heat affected zone and the thermal-mechanical affected zone was the softest region, where the cracks of friction stir spot microwelds in the lap-shear specimens under the loadings initiated and leaded to fracture of the specimens.

Modeling of the fracture behavior of spot welds using advanced micro-mechanical damage models

This paper presents the modeling of deformation and fracture behavior of resistance spot welded joints in DP600 steel sheets. Spot welding is still the most commonly used joining technique in automotive engineering. In overloading situations like crash joints are often the weakest link in a structure. For those reasons, crash simulations need reliable and applicable tools to predict the load bearing capacity of spot welded components. Two series of component tests with different spot weld diameters have shown that the diameter of the weld nugget is the main influencing factor affecting fracture mode (interfacial or pull-out fracture), load bearing capacity and energy absorption. In order to find a correlation between nugget diameter, load bearing capacity and fracture mode, the spot welds are simulated with detailed finite element models containing base metal, heat affected zone and weld metal in lap-shear loading conditions. The change in fracture mode from interfacial to pull-out or peel-out fracture with growing nugget diameter under lap-shear loading was successfully modeled using the Gologanu-Leblond model in combination with the fracture criteria of Thomason and Embury. A small nugget diameter is identified to be the main cause for interfacial fracture. In good agreement with experimental observations, the calculated pull-out fracture initiates in the base metal at the boundary to the heat affected zone.

Laser bonding and characterization of Kapton® FN/Ti and Teflon® FEP/Ti systems

Kapton® FN and Teflon® FEP (fluorinated ethylene propylene) polymers are resistant to most chemical solvents, heat sealable, and have low moisture uptake, which make them attractive as packaging materials for electronics and implantable devices. Kapton® FN/Ti and Teflon® FEP/Ti microjoints were fabricated by using focused infrared laser irradiation. Laser-bonded samples were tested with a micro-testing machine under lap shear load and the bond strength was determined. The bond strength for the Kapton® FN/Ti and Teflon® FEP/Ti systems was found to be 3.32 and 8.48 N/mm2, respectively. The failure mode of the mechanically tested samples was studied by using optical microscopy and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. Chemical interactions during laser bonding of Kapton® FN to titanium were studied by using X-ray photoelectron spectroscopy (XPS). The XPS results give evidence for the formation of Ti–F bonds in the interfacial region.

Joint strength and failure mechanism of laser spot weld of mild steel sheets under lap shear loading

Ultimate strength and failure mechanism of laser spot welds under lap shear loading were investigated. Optical micrographs of cross-section of spot welds before and after failure were examined to understand the failure behaviour. The experimental results indicate that laser spot welds can fail in two distinct modes, namely interfacial and pullout failure. A failure mechanism which was confirmed by SEM investigations was proposed to describe these two failure modes. According to the experimental observations, a simple stress solution related to the far field load was conducted and the critical weld nugget diameter to ensure pullout failure mode was estimated. The results were compared with the experimental data and also with the test data of resistance spot welds. It was observed that the critical nugget diameter of laser spot welding was larger than that of resistance spot welding due to the different failure location in pullout mode. Furthermore, the effect of welding parameters on joint strength and failure mode was studied.

Experimental study of joint performance in spot friction welding of 6111-T4 aluminium alloy

The effect of process parameters (cycle time, tool speed and axial force) on the specimen temperature measured 2 mm away from the weld in spot friction welding (SFW) of Al 6111-T4 is investigated. The temperatures were correlated to the lap shear load. Results revealed that, to achieve a good joint strength with the maximum lap shear load >2˙5 kN, temperatures should be greater than a threshold value, which is 350°C at a location close to the SFW joint in this study. By studying the specimen macrographs, two internal weld geometric features based on the cross-section area were identified and correlated to the shear and mixed failure modes of the lap shear tested specimens. A model was developed and validated using experimental data of the cross section area of SFW joint with either shear or mixed mode fracture. The model predicts that the SFW joint strength is maximised at the transition region between the shear and mixed mode fracture.

Effects of processing time on strengths and failure modes of dissimilar spot friction welds between aluminum 5754-O and 7075-T6 sheets

The effects of the processing time on the strengths and failure modes of two types of dissimilar spot friction welds between aluminum 5754-O and 7075-T6 sheets are investigated by experiments. Dissimilar 5754/7075 and 7075/5754 spot friction welds made at different processing conditions were tested under lap-shear loading conditions. The experimental results indicate that the failure loads of both types of welds in lap-shear specimens increase when the processing time increases for the given ranges of the processing time. 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. Selected optical and scanning electron micrographs of both types of welds made at different processing times before and after failure are examined. The micrographs show different weld geometries and different failure modes of the welds made at different processing times. The failure modes of the dissimilar 5754/7075 and 7075/5754 spot friction welds are quite complex and appear to strongly depend on the geometry and strength of the interfacial surface between the two deformed sheet materials.

Strength assessment of adhesive-bonded joints

This paper deals with non-linear analyses of adhesively bonded joints under tensile lap shear loading. 3D FEM models are taken into account. The effect of the number of elements through the adhesive layer thickness is considered. Tensile true stress–true strain curves are used as models of the adherend and adhesive materials. The single lap joints are tested to validated the numerical analyses. Comparison between one-step and two-step loading is considered. In the two-step loading, a uniform displacement in the transversal direction in the one grip region is applied, followed by a tensile loading. The uniaxial load is applied gradually until the joint fails due to large plastic deformation. Non-linear analyses and laboratory tests were performed for two different adhesive thickness (0.2 and 0.03 mm). The results of laboratory tests are complied with the results of finite element simulations. The authors offer method which will be used to modelling the steel-composite bonded structure subjected to multiaxial loads.

Effects of fusion zone size and failure mode on peak load and energy absorption of advanced high strength steel spot welds under lap shear loading conditions

This paper examines the effects of fusion zone size on failure modes, static strength and energy absorption of resistance spot welds (RSW) of advanced high strength steels (AHSS) under lap shear loading condition. DP800 and TRIP800 spot welds are considered. The main failure modes for spot welds are nugget pullout and interfacial fracture. Partial interfacial fracture is also observed. Static weld strength tests using lap shear samples were performed on the joint populations with various fusion zone sizes. The resulted peak load and energy absorption levels associated with each failure mode were studied for all the weld populations using statistical data analysis tools. The results in this study show that AHSS spot welds with conventionally required fusion zone size of 4 t cannot produce nugget pullout mode for both the DP800 and TRIP800 welds under lap shear loading. Moreover, failure mode has strong influence on weld peak load and energy absorption for all the DP800 welds and the TRIP800 small welds: welds failed in pullout mode have statistically higher strength and energy absorption than those failed in interfacial fracture mode. For TRIP800 welds above the critical fusion zone level, the influence of weld failure modes on peak load and energy absorption diminishes. Scatter plots of peak load and energy absorption versus weld fusion zone size were then constructed, and the results indicate that fusion zone size is the most critical factor in weld quality in terms of peak load and energy absorption for both DP800 and TRIP800 spot welds.

Microstructures and failure mechanisms of friction stir spot welds of aluminum 6061-T6 sheets

Microstructures and failure mechanisms of friction stir spot welds in aluminum 6061-T6 lap-shear specimens are investigated based on experimental observations. Optical micrographs of the cross-sections of friction stir spot welds in lap-shear specimens before and after failure are examined. These friction stir spot welds show the failure mode of nugget pullout under lap-shear loading conditions. The experimental observations suggest that under lap-shear loading conditions, the failure is initiated near the possible original notch tip in the stir zone (SZ) and the failure propagates along the circumference of the nugget to final fracture. Microindentation hardness data of base metal (BM), heat affected zone (HAZ), thermal–mechanical affected zone (TMAZ) and SZ are obtained. The interface between the HAZ and the TMAZ is the softest region, where the cracks of friction stir spot welds in the lap-shear specimens under the loadings initiate and lead to fracture of the specimens.

Evaluation of high-performance pressure-sensitive adhesives and VHB™ acrylic foam tapes bonded aluminum joints subjected to environmental aging

A range of 3M™ high performance pressure-sensitive adhesives (PSAs) and 3M™ VHBTM™ acrylic foam tapes were used to bond 25.4 mm × 3.175 mm aluminum 2024 T-4 adherends in both single-lap joint (SLJ) and three-point end-notch flexure (ENF) configurations. The samples were subjected to two types of aggressive environments to simulate extreme service conditions: freeze–thaw and heat–cool cycling, both for 21 days. Impulse-frequency response vibration and electrochemical impedance spectroscopy (EIS) were used for monitoring bond quality non-destructively. Data were first obtained on a set of specimens at room conditions (i.e., before being subjected to freeze–thaw, or heat–cool cycling), referred to as "baseline" in this paper. After obtaining baseline data, several batch sets were subjected to quasi-static lap-shear and dynamic impact loadings to compare the mechanical and electrochemical properties before and after environmental cycling. EIS results show that moisture absorption caused a reduction in low-frequency impedance, whereas decrease in adhesive thickness caused a reduction of impedance over the entire frequency range. The impulse-frequency response vibration NDE technique was able to detect the changes in loss factor (damping) of adhesive joints after environmental aging. Quasi-static lap-shear loading of SLJs showed that acrylic foams took less failure load compared to PSA tapes, and SLJs subjected to dynamic impact showed all PSAs and acrylic foams taking about the same impact load to failure, except the softer acrylic foam.