Tensile Shear Load Research Articles

Experimental study of nanoelectroplating steel spot welding structure under impact tensile-shear loading

The tensile shear fracture behavior of solder joints under impact load influences the whole vehicle’s safety substantially. This paper takes the QP980 steel resistance spot welding (RSW) structure as the research object to study the tensile-shear fracture behavior of the RSW structure under tensile-shear loading. The microstructure observation of the welded spot shows that the metallographic structure is the martensite. The porosity defects in the melting zone are the primary defect reflecting the obvious plate-cracks on both sides of the nugget. The paper demonstrates the Vickers hardness test result of the spot-welded zone. According to the test, the micro-hardness distribution result shows that the higher the martensite, the greater the hardness. A softened zone emerges adjacent to the heat-affected zone on the welded base material interface. The quasi-static and dynamic tensile-shear tests on the QP980 steel RSW lap-joint specimens show that the fracture on the BM is adjacent to the welded spot under quasi-static loading but close to the heat-affected zone under dynamic loading. Under dynamic loading, the weld seam and softened zone of the welded spot have a direct influence on the fracture. On the recovered specimen’s fractured section, there are a large number of apparent dimples on the section of the BM under quasi-static loading and the section of the HAZ under dynamic loading with nucleation, growth, and aggregation of cavitation, resulting in ductile fracture.

Investigation into the Effect of RFSSW Parameters on Tensile Shear Fracture Load of 7075-T6 Alclad Aluminium Alloy Joints.

The aim of the investigations was to determine the effect of parameters of refill friction stir spot welding (RFSSW) on the fracture load and failure mechanisms of the resulting joint. RFSSW joints were made in 7075-T6 Alclad aluminium alloy sheets using different welding parameters. The load capacity of joints was determined under tensile/shear loadings. Finite element-based numerical simulations of the joint-loading process were carried out, taking into account the variability of elasto-plastic properties of weld material through the joint cross-section. The influence of welding parameters on selected phenomena occurring during the destruction of the joint is presented. The considerations were supported by a fractographic analysis based on SEM images of fractures. It was found that there is a certain optimal amount of heat generated, which is necessary to produce the correct joint in terms of its load capacity. This value should not be exceeded, because it leads to weakening of the base material and thus to a reduction in the strength of the joint. Samples subjected to uniaxial tensile shear load showed three types of failure mode (tensile fracture, shear fracture, plug type fracture) depending on the tool rotational speed and duration of welding. Prediction of the fracture mode using FE-based numerical modelling was consistent with the experimental results. The samples that were damaged due to the tensile fracture of the lower sheet revealed a load capacity (LC) of 5.76 KN. The average value of LC for the shear fracture failure mechanism was 5.24 kN. The average value of the LC for plug-type fracture mode was 5.02 kN. It was found that there is an optimal amount of heat generated, which is necessary to produce the correct joint in terms of its LC. Excessive overheating of the joint leads to a weakening of the base metal and thus a reduction in the strength of the joint. Measurements of residual stresses along the axis specimens showed the presence of stresses with a certain constant value for the welded area on the side of the 1.6 mm thick plate.

A comparative study on microstructural and mechanical behaviour of spot welded Ti-6Al-4V alloy in as-welded and solution treated condition

ABSTRACT The current experimentation emphasises on the diversification in metallurgical transformation under solution treatment, which governs the solidification rate and can trigger the final mechanical behaviour of the welded structure. In the present work, a thin sheet (750 μm) of Ti-6Al-4V alloy is joined using resistance spot welding process in overlap configuration at varied weld time cycles of 30, 50, and 70. Further, in order to explore metallurgical aspects and associated influence on mechanical behaviour, post-weld heat treatment (PWHT) is performed. The weld pad is heated up to -transus temperature (~915°C) for 60 min, consequently cooled by water quenching method. It is opined that the welding heterogeneity that arises at welding can be homogenised by gradual heating and cooling cycles in the PWHT cycle. Upon increasing weld time from 50 → 70 cycles, mechanical properties are improved. Therefore, 70 cycles is regarded as the optimised weld time. Coarsening of -lath within the prior -grain boundary is confirmed in the weld zone of as-welded specimens. On the other hand, application of solution treatment found is to be advantageous since it changes the mode of failure from interfacial to pullout, which is always desirable. Improved tensile-shear load bearing capacity (TSLBC) and extension are indicated by pullout failure accompanied by solution treatment.

The experimental study of CFRP interlayer of dissimilar joint AA7075-T651/Ti-6Al-4V alloys by friction stir spot welding on mechanical and microstructural properties

AbstractThe present study focused on two dissimilar metal alloys: AA7075-T651 and Ti-6Al-4V alloys with additional carbon fiber-reinforced polymer (CFRP) as an interlayer were welded together by friction stir spot welding (FSSW). The effect of welding parameters (rotational speed and dwell time) and carbon fiber-reinforced polymer on mechanical and microstructural properties of a weld joint was investigated. The obtained results explore the parametric effects on mechanical properties of the weld joint. The maximum tensile shear load 2597.8 N was achieved at the rotational speed of 2,000 rpm and dwell time of 10 s. While at the same rotational speed, 54.7% reduction in the tensile shear load was attained at shorter dwell time of 5 s. Therefore, dwell time plays an important role in the tensile shear load of a weld joint. The scanning electron microscope (SEM-EDS) results show the formation of intermetallic compound of Ti3Al and Ti-Al-C that significantly affect the mechanical and microstructural properties of the weld joint. Moreover, the effect of the rotational speed on micro-hardness was found at significant than dwell time. The micro-hardness of the weld joint increase by 18.90% in the keyhole rather than the stir zone and the thermomechanical affected zone, which might be due to the presence of ternary (Ti-Al-C) intermetallic compound.

Joint Properties of Aluminum Alloy and Galvanized Steel by AC Pulse MIG Braze Welding

In response to global environment and fuel efficiency regulations aiming to reduce CO2 emissions, multi-material structures that use lightweight materials are currently being developed to realize the weight reduction of vehicles in automotive manufacturing. The dissimilar welding of aluminum alloy to steel has great importance, but it is still challenging due to their widely varying thermo-physical properties and the formation of intermetallic compounds. This study aimed to investigate the effect of process parameters on the wettability, mechanical properties, and microstructure in AC Pulse MIG welded joints of AA6061-T6 and galvanized steel sheets. A parametric study on torch aiming position and welding current with EN ratio variation was performed to optimize the process parameters. The result showed that the amount of metal deposition increased with EN ratio. When the EN ratio was higher, the wire feeding speed increased and the heat input process lowered. Moreover, the wetting length increased, ranging from 6.6 to 8.4 mm, and the wetting angle increased from 31.2 to 67.6°, respectively. As a result of the tensile shear test, the maximum tensile shear load of dissimilar welded joints produced at 70 A with a 20% EN ratio was approximately 8.8 kN. From the result of scanning electron microscopy with energy-dispersive spectrometry, FeAl3 IMC was observed at the joint interface, and the IMC layer thickness decreased with EN ratio at 70 A.

Microstructural Evaluation and Influence of Welding Parameters on Electrode Plunge Depth in Resistance Spot Welded Dissimilar DP800HF/1200M Steel Joints

Advanced high strength steels (AHSS) are newly developed steels that has versatile mechanical properties. These steels enables to design low weight cars with high safety standards. Also, weight reduction in vehicles plays a significant role for saving fossil fuels which is limited and causes carbon emissions. Dual phase (DP) and Martensitic steels are prominent in AHSS family because they are inexpensive and has vast application areas. DP steels are used for general purpose applications and Martensitic steels are used for reinforcement parts in vehicles. In this study, high formable grade Dual phase steel with 800 MPa tensile strength and Martensitic steel with 1200 MPa tensile strength were welded with resistance spot welding technique which is the most widely practiced joining method in the industry. Electrode indentation depths, its effect on tensile-shear loads and microstructural characterizations were investigated. According to the results, the lowest tensile shear loads were acquired between both between 0-0.2 mm and between 0.85-1mm electrode plunge depths. Medial electrode plunge depths showed high tensile shear loads. Some welding defects were encountered including secondary phase formations, shrinkage voids, intergranular shrinkage gaps and vertical cracks in the weld nugget. It is find out that the weld defects were formed due to cooling gradient while solidifying, electrode force, and improper weld parameters.

Bond strength and bonding interface of Ni/Al dissimilar joint by spot forge-welding

Nickel and aluminum lap joining of a 1-mm-thick sheet each was performed using the spot forge-welding method. Direct joining was conducted with an 8-mm-diameter punch in a bonding time of 77 ms. The tensile shear load of the joint reached 5.3 kN, and the 107 fatigue limit in cyclic tension was 1.3 kN. In each of the fracture forms, base metal fracture on the aluminum side was realized. The reaction layer at the bonding interface had a thickness of 400–500 nm and was divided into two layers. This result is expected to be useful in next-generation spot solid-phase bonding methods, for high throughput production of electrical parts and electrodes that realize high-strength dissimilar material bonding.

Experimental evaluation and theoretical prediction of elastic properties and failure of C/C‐SiC composite

AbstractThe paper presents experimental characterization and theoretical predictions of elastic and failure properties of continuous carbon fiber reinforced silicon carbide (C/C‐SiC) composite fabricated by Liquid Silicon Infiltration (LSI). Its mechanical properties were determined under uniaxial tensile, compression, and pure shear loads in two sets of principal coordinate systems, 0°–90° and ±45°, respectively. The properties measured in the 0°–90° coordinate system were employed as the input data to predict their counterparts in the ±45° coordinate system. Through coordinate transformations of stress and strain tensors, the elastic constants and stress‐strain behaviors were predicted and found to be in good agreement with the experimental results. In the same way, three different failure criteria, maximum stress, Tsai‐Wu, and maximum strain, have been selected for the evaluation of the failure of C/C‐SiC as a type of genuinely orthotropic material. Based on the comparisons with experimental results, supported by necessary practical justifications, the Tsai‐Wu criterion was found to offer a reasonable prediction of the strengths, which can be assisted by the maximum stress criterion to obtain an indicative prediction of the respective failure modes.

A novel hybrid damage monitoring approach to understand the correlation between size effect and failure behavior of twill CFRP laminates

Despite the presence of numerous studies about size effect in composite materials, controversy still exists regarding the relation between mechanical behavior and size of the laminates. Therefore, in this study, a comprehensive experimental approach using combined structural health monitoring techniques namely, acoustic emission, digital image correlation and infrared thermography is conducted to elucidate the physics behind size effect in twill woven carbon fiber reinforced polymeric composites. Laminates with different thicknesses are produced and tested under tensile and in-plane shear loading conditions. In depth analysis of the acoustic emission data shows that an increase in the thickness of laminate changes the fraction of microdamage related to fiber failures. Moreover, a noticeable stagnation period in acoustic emission activity prior to global failure is observed for thick samples which is negligible for thin specimens. Furthermore, analysis of damage accumulation rate via acoustic emission technique is cross validated with digital image correlation and thermography for tensile and shear test results. The full field monitoring results indicate the inverse relation between the thickness of the laminates and damage growth rate. The combined usage of damage monitoring techniques shows that thicker laminates experiences slower damage growth dynamics as compared to those of thin laminates, thereby, assisting to understand the size effect in laminated composites.

Strength improvement in friction stir spot joining of polyethylene and aluminum

Abstract The effect of surface condition, dwell time and plunge rate on the mechanical properties of dissimilar joints between polyethylene and aluminum were investigated. The scratches made by the mandrels on the aluminum surface acted as mechanical locks and hence the strength of the dissimilar joint was increased. An increased dwell time and a decreased plunge rate exhibited a positive effect on the bond strength values. The major joining mechanisms were mechanical interlocking between the sheets and wetting of the aluminum surface by the molten polyethylene. The increase in the actual contact area due to the increased surface roughness, improved the shear-tensile load of the joint (up to 56%).

Load Path Transmission in Joining Elements

The mechanical properties of joined structures are determined considerably by the chosen joining technology. With the aim of providing a method that enables a faster and more profound decision-making in the spatial distribution of joining points during product development, a new method for the load path analysis of joining points is presented. For an exemplary car body, the load type in the joining elements, i.e. pure tensile, shear and combined tensile-shear loads, is determined using finite element analysis (FEA). Based on the evaluated loads, the resulting load paths in selected joining points are analyzed using a 2D FE-model of a clinching point. State of the art methods for load path analysis are dependent on the selected coordinate system or the existing stress state. Thus, a general statement about the load transmission path is not possible at this time. Here, a novel method for the analysis of load paths is used, which is independent of the alignment of the analyzed geometry. The basic assumption of the new load path analysis method was confirmed by using a simple specimen with a square hole in different orientations. The results presented here show a possibility to display the load transmission path invariantly. In further steps, the method will be extended for 3D analysis and the investigation of more complex assemblies. The primary goal of this methodical approach is an even load distribution over the joining elements and the component. This will provide a basis for future design approaches aimed at reducing the number of joining elements in joined structures.

Friction stir spot welding of AA5052 with additional carbon fiber-reinforced polymer composite interlayer

AbstractIn this study, similar aluminum alloys AA5052 with additional carbon fiber-reinforced polymer composite (CFRP) interlayer were selected to investigate the effect of welding parameters (rotational speed and dwell time) on the mechanical properties, joint efficiency, and microstructure of friction stir spot weld joint. The maximum tensile shear load was 1779.6 N with joint efficiency of 14.6% obtained at rotational speed of 2,000 rpm and 2 s dwell time, which is 39.5% higher than the value at low rotational speed 850 rpm and 2 s dwell time. Meanwhile, the maximum microhardness 58 HV was attained in the keyhole region at rotational speed of 2,000 rpm and dwell time of 5 s, which is 22.4% higher compared to low rotational speed. The SEM-EDS results reveal the presence of intermetallic compounds (Al–Mg–C), which enhance the intermetallic bonding between elements.

Comparison of two criteria of stress intensity factor and fracture energy to investigate the behavior of asphalt mixtures under combined tensile-shear loading modes-A statistical approach

Fracture energy and stress intensity factor are of the most prevalent criteria for determining the fracture behavior of asphalt mixtures. In this research, the fracture performance of asphalt mixtures under different modes of loading at different temperatures and loading rates was investigated, and the stress intensity factor and fracture energy were determined and compared to the fracture resistance criteria. For this purpose, loading modes of pure tension, pure shear and four different mixed shear-tension loading conditions were chosen, and the fracture tests were conducted on the SCB specimens at temperatures of −5 ℃, −15 ℃ and −25 ℃, loading rates of 1 and 5 mm/min and different loading modes. The results showed that the fracture behavior of asphalt mixtures is significantly dependent on testing temperature and loading rate. The studied parameters of fracture energy and stress intensity and the correlation between them are functions of the loading mode, loading speed, and testing temperature. Moreover, the changing trends of the parameters of fracture energy and stress intensity factor do not necessarily follow the same trend and each factor represents a specific concept of fracture performance of asphalt mixtures.

Improving the Tensile Shear Load of Al–Mg–Si Alloy FSLW Joint by BPNN–GA

In order to obtain the joint with a high tensile shear load, the small penetration of tool pin into the lower sheet was applied during friction stir lap welding. The tensile shear loads of the Al–Mg–Si aluminum alloy joint under different process parameter combinations were optimized by combining back propagation neural network and genetic algorithm. The result showed that the hook bent down and the height of cold lap was small. Under the external tension load, the crack propagated along the lap interface or extended downward after reaching the highest point along the cold lap. With the increase of heat input, the tensile fracture mode of joint was more easily obtained. The highest tensile shear load of the joint reached 12.45kN, which was increased by 6.9% than the maximum value before optimization.

Characterization of Polypropylene Sheet Friction Stir Spot Welded Joint

A study to determine the effect of rotational speed and geometric shape of a tool on the mechanical properties of polypropylene joint using the FSSW technique has been carried out. A polypropylene sheet was cut into pieces with a dimension of 150 x 30 x 5 mm. A medium carbon steel bar was machined to fabricate welding tools. Two types of devices with shoulder angles of 0° and 5° were prepared, while the other parametric geometries were the same. While the friction stir spot welding (FSSW) process has been carried out at variations of rotational speeds of 985, 1660, and 2350 rpm, the other welding process parameters, such as tool plunge rate, dwell time, and delay time, were considered constant. The tensile shear load capacity, macrostructure, hardness, and failure mode of the joint results were then evaluated. The results revealed that using a pin tool with a shoulder angle of 5° achieved a maximum tensile shear load capacity at a rotational speed of 2350 rpm with a result of 2253 N due to its wider nugget area. The load capacity increased with the increase of rotational speed. A pin tool angle of 15° with a shoulder angle of 5° may be suggested for the tool’s chosen geometry.

Effect of tool plunge depth on the microstructure and fracture behavior of refill friction stir spot welded AZ91 magnesium alloy joints

We used refill friction stir spot welding (RFSSW) to join 2-mm-thick AZ91D-H24 magnesium alloy sheets, and we investigated in detail the effect of tool plunge depth on the microstructure and fracture behavior of the joints. A sound joint surface can be obtained using plunge depths of 2.0 and 2.5 mm. Plunge depth was found to significantly affect the height of the hook, with greater plunge depths corresponding to more severe upward bending of the hook, which compromised the tensile-shear properties of the joints. The hardness reached a minimum at the thermo-mechanically affected zone due to the precipitation phases of this zone as it dissolved into the α-matrix during the welding process. The fracture modes of RFSSW joints can be divided into three types: shear fracture, plug fracture, and shear—plug fracture. Of these, the joint with a shear—plug fracture exhibited the best tensile-shear load of 6400 N.

Dieless Friction Stir Extrusion-Brazing (DFSE-B) of AA2024-T3 aluminum alloy to Copper with Zn interlayer

The integration of flow-induced mechanical interlocking, interlayer-controlled atomic diffusion and self-reacting brazing benefit is employed to achieve an improved load-bearing performance of the dissimilar AA2024-T3/copper joint via the use of Dieless Friction Stir Extrusion-Brazing (DFSE-B). A comparative study of the Dieless Friction Stir Extrusion-Brazing (DFSE-B) and Friction Stir Spot Welding-Brazing (FSSW-B) of the dissimilar AA2024-T3/Cu joint was investigated by using a 100 µm thick Zn interlayer. The microstructure, tensile-shear load, and fracture modes of the respective joints were examined. The results show that Zn solidification-induced voids are inevitable at the brazed zones of both joints and the DFSE-B process suppresses flow-induced defect, unlike the FSSW-B process. An improved tensile-shear load with a significant toughness is achieved by the DFSE-B process due to the absence of tool-induced keyhole, and the intrinsic mechanical interlocking of the softer Al alloy into the harder Cu alloy. The DFSE-B is a suitable welding alternative for reactive metals.

Load distributions in bolted single lap joints under non-central tensile shear loading

This study uses a numerically calibrated beam theory-based model to investigate a bolt load distributions in a preloaded two-bolt single lap joint under non-central tensile shear loading. Linear spring-based modeling is used for the two preloaded bolts and substrates. Non central loading may be due to geometric tolerances that would cause additional moment loading on the joint. Thus, the load would not be equally distributed among all bolts in the joint. The effect of various joint parameters, bolt preload and off-center location of the tensile shear loading is investigated and discussed.

The Effect of Welding Current and Electrode Force on the Heat Input, Weld Diameter, and Physical and Mechanical Properties of SS316L/Ti6Al4V Dissimilar Resistance Spot Welding with Aluminum Interlayer.

Welding parameters obviously determine the joint quality during the resistance spot welding process. This study aimed to investigate the effect of welding current and electrode force on the heat input and the physical and mechanical properties of a SS316L and Ti6Al4V joint with an aluminum interlayer. The weld current values used in this study were 11, 12, and 13 kA, while the electrode force values were 3, 4, and 5 kN. Welding time and holding time remained constant at 30 cycles. The study revealed that, as the welding current and electrode force increased, the generated heat input increased significantly. The highest tensile-shear load was recorded at 8.71 kN using 11 kA of weld current and 3 kN of electrode force. The physical properties examined the formation of a brittle fracture and several weld defects on the high current welded joint. The increase in weld current also increased the weld diameter. The microstructure analysis revealed no phase transformation on the SS316L interface; instead, the significant grain growth occurred. The phase transformation has occurred on the Ti6Al4V interface. The intermetallic compound layer was also investigated in detail using the EDX (Energy Dispersive X-Ray) and XRD (X-Ray Diffraction) analyses. It was also found that both stainless steel and titanium alloy have their own fusion zone, which is indicated by the highest microhardness value.

Effects of welding parameters on tensile properties and fracture modes of resistance spot welded DP1200 steel

Abstract In this study, the maximum tensile shear load bearing capacity and fracture modes of resistance spot welded DP1200 steel were investigated, and the tensile shear properties of the joints were evaluated. The effects of different welding parameters on tensile shear properties, fracture modes, microstructure, microhardness, and heat affected zone softening were examined. Weld processes were performed by using 2 to 6 bar electrode pressure as well as 5 and 7 kA weld currents. The microstructure of resistance spot welded materials was evaluated, and the hardness profiles were determined. Experimental results showed that welding current and electrode pressure had a significant effect on the load-displacement characteristics of DP1200 welds. Three different fracture modes were observed in the tensile shear loads. It was also observed that the expulsion had a negative effect on the tensile shear properties.