Tensile Shear Load Bearing Capacity Research Articles

An Optimization Study on Resistance Spot Welding of DP600 Sheet Steel via Experiment and Statistical Analysis

Resistance Spot Welding (RSW) is widely used in many automotive, boiler, and ship manufacturing industries. Therefore, the optimization and effectiveness of the RSW process are very useful and cost-efficient processes in addition to improving weld quality. This study used various welding parameters to investigate the optimization of the RSW process of Advanced High Strength Steel (AHSS). RSW was carried out using different welding times, currents, and electrode pressure values. Microstructural analysis, nugget formation, and tensile shear test were performed on samples. This study applied the Taguchi method and ANOVA to set up the welding process and optimize its results. Microstructural characterization showed that the weld nugget microstructures had a high-volume fraction of martensite. Using the Minitab software, Taguchi (DOE) and ANOVA on the tensile shear test results showed that welding current is more effective than clamping pressure on the tensile shear load-bearing capacity (TLBC). However, clamping pressure affects the weld current effects on weld performance. Additionally, the TLBC of RSW samples increases, whereas increasing the clamping pressure leads to a decrease in TLBC and nugget dimensions. Consequently, a detailed analysis of the RSW coefficients and their effects led to optimized results.

Quality prediction and classification of resistance spot weld using artificial neural network with open-sourced, self-executable and GUI-based application tool Q-Check

Optimizing Resistance spot welding, often used as a time and cost-effective process in many industrial sectors, is very time-consuming due to the obscurity inherent within process with numerous interconnected welding parameters. Small changes in values will give effect to the quality of welds which actually can be easily analysed using application tool. Unfortunately, existing software to optimize the parameters are expensive, licensed and inflexible which makes small industries and research centres refused to acquire. In this study, application tool using open-sourced and customized algorithm based on artificial neural networks (ANN) was developed to enable better, fast, cheap and practical predictions of major parameters such as welding time, current and electrode force on tensile shear load bearing capacity (TSLBC) and weld quality classifications (WQC). A supervised learning algorithm implemented in standard backpropagation neural network gradient descent (GD), stochastic gradient descent (SGD) and Levenberg–Marquardt (LM) was constructed using TensorFlow with Spyder IDE in python language. All the display and calculation processes are developed and compiled in the form of application tool of graphical user interface (GUI). Results showed that this low-cost application tool Q-Check based on ANN models can predict with 80% training and 20% test set on TSLBC with an accuracy of 87.220%, 92.865% and 93.670% for GD, SGD and LM algorithms respectively while on WQC 62.5% for GD and 75% for both SGD and LM. It is also expected that tool with flexible GUI can be widely used and enhanced by practitioner with minimum knowledge in the domain.

EFFECT OF SHIELDING GAS ON THE PROPERTIES OF STAINLESS-STEEL SUS 304L PLUG WELDED

The effect of shielding gas composition and welding current on the mechanical-physical properties of plug welding joint stainless steel SUS 304L has been investigated. Metal Inert Gas (MIG) welding was used to join SUS304L with a thickness of 3 mm. The variations of welding current were 80 A, 100 A, and 120 A, while variations of shielding gas composition were 100% Ar; 92,5% Ar-7,5% CO2; 85% Ar-15% CO2; 77,5% Ar-22,5% CO2; 100% CO2. Macro and microstructural tests were conducted to determine welded joints physical properties. Tensile-shear testing and micro hardness Vickers were done to determine welded joints physical properties. The results show that the higher level of welding current and CO2 content in the shielding gas, the more tensile-shear load bearing capacity and decreased hardness. The welding current of 120 A and shielding gas 77,5% Ar-22,5% CO2 produced welded joints with the highest tensile-shear load bearing capacity. The nugget size increased as the higher level of welding current and the CO2 content in the shielding gas due to the increase of heat input.

Glass-box modeling for quality assessment of resistance spot welding joints in industrial applications

Resistance spot welding (RSW) is one of the most relevant industrial processes in different sectors. Key issues in RSW are process control and ex-ante and ex-post evaluation of the quality level of RSW joints. Multiple-input–single-output methods are commonly used to create predictive models of the process from the welding parameters. However, until now, the choice of a particular model has typically involved a tradeoff between accuracy and interpretability. In this work, such dichotomy is overcome by using the explainable boosting machine algorithm, which obtains accuracy levels in both classification and prediction of the welded joint tensile shear load bearing capacity statistically as good or even better than the best algorithms in the literature, while maintaining high levels of interpretability. These characteristics allow (i) a simple diagnosis of the overall behavior of the process, and, for each individual prediction, (ii) the attribution to each of the control variables—and/or to their potential interactions—of the result obtained. These distinctive characteristics have important implications for the optimization and control of welding processes, establishing the explainable boosting machine as one of the reference algorithms for their modeling.

Investigation of Diffusion Welding Capability of WC Ceramic Based Ni Doped Composites

In this study, sample pairs of (WC) Ni / (WC) Ni and WC-Ni / WC-Ni formed from (WC) Ni composites produced from Ni coated WC powders and uncoated WC-Ni / powders were used for diffusion welding. Diffusion welding was carried out by preloaded compression system under Ar atmosphere. Diffusion welding was obtained by changing bonding pressure and temperature. Schimadzu 100kN universal tensile machine was employed for tensile shear testing of diffusion welded couples. The tensile shear test results showed that electroless nickel coated WC(Ni) composite diffusion couples yielded best tensile shear load bearing capacity 35,4 MPa compared to other diffusion couples. Hardness values ranging from 200 to 400HV were determined. SEM and XRD analysis systems were used to analyze the microstructural analysis of the composites and diffusion welded samples obtained in the study and to analyze the particles formed at the weld interface.

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.

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.

Tensile and fatigue behavior of resistance spot-welded HSLA steel sheets: Effect of pre-strain in association with dislocation density

In the automotive applications, sheet metals are inevitably subjected to pre-straining during stamping operation prior to spot welding. The integrity of vehicles is governed by the static and fatigue strengths of the joints. However, the effect of pre-strain on the tensile and fatigue properties of the spot-welds on the high strength low alloy (HSLA) steel sheets has not been well studied. To abridge this gap, steel sheets of 1.2 mm thickness in as-received condition as well as after pre-straining to three different levels of 5%, 10%, and 15% were spot-welded in the form of lap-shear joints. With an increase in pre-strain, the load-bearing capacity of the joints monotonically increased, while there was no significant effect of pre-strain on the fatigue behavior and endurance limit of the joints. This difference in tensile-shear and fatigue behavior of the joints for pre-strained samples is attributed to the variation in the location of the failure, which has been explained in terms of the difference in failure mechanisms involved with the tests. The crack initiated at the base metal in case of tensile-shear tests, whereas under cyclic loading, fatigue cracks initiated between fine-grained heat affected zone (FGHAZ) and coarse grain heat affected zone (CGHAZ) located near the interfacial notch between the two welded sheets. While the location of failure in tensile-shear test is dictated by its lower strength across the joint, that in fatigue test is governed by the stress concentration. The magnitude of dislocation density has been evaluated quantitatively in the base metal, heat affected zone (HAZ), and fusion zone of weld joint using X-ray diffraction (XRD), and the dislocation substructures have been examined by transmission electron microscopy (TEM). The increase in tensile-shear load-bearing capacity is due to increased dislocation density in base metal with pre-strain. As most of these dislocations generated due to the pre-straining are annihilated at the HAZ during welding, there was no significant effect of pre-strain on the fatigue strength of the joints. These results were corroborated by microstructural examination and micro-hardness measurements across the weld joints in as-received and pre-strained conditions.

Fatigue Properties of Resistance Spot Welded Dissimilar Interstitial-Free and High Strength Micro-Alloyed Steel Sheets

This study aims to investigate the influence of nugget diameter on tensile-shear and fatigue properties of the dissimilar resistance spot-welded joints of interstitial free and high strength niobium microalloyed steel sheets. The spot-weldings are done at currents of 7 kA and 9 kA at welding time of 300 ms with electrode force of 2.6 kN. Fatigue tests are done at different load amplitudes, considering the maximum tensile-shear load bearing capacity of the joints. The tests are interrupted before the final failure to understand the crack initiation and propagation paths. The study is supplemented by the microstructural and detailed fractographic analyses. The results indicated that the fatigue strength of the spot-welds increased with a decrease in nugget diameter. This could be attributed to the higher microhardness of heat affected zone (HAZ), presence of compressive residual stress and lower variation in thickness reduction on the IF steel side, welded at 7 kA. However, the tensile-shear load bearing capacity of the spot-welds increased with increase in the nugget diameter. The failure of the spot-welded joint under static loading initiates from the HAZ/base metal interface of the IF steel side. Nevertheless, under cyclic loading crack initiates from the notch root at the interface of two sheets lying in the HAZ of IF steel side. Fractographic investigations indicate intergranular fracture features in combination with striations, secondary cracks on the IF steel side under cyclic loading. Fracture surfaces of the specimens failed under static loading shows however, shear dimples on the IF steel side.

RSW Junctions of Advanced Automotive Sheet Steel by Using Different Electrode Pressures

Based on this study, the effects of the different types of welding currents and electrode pressures on the tensile shear properties of the resistance spot welding (RSW) which are the joints of the commercial DP600 sheet steel are now been investigated. In addition to the fact that the electrode pressure is not much of a popular piece or topic of discussion in the literature, the expression of the mechanical properties of these commercial materials (most importantly in the DP and in the high strength steels). These factors that are known to be affecting the strength of the material are dispute. In the tensile shear tests of this welded joints; the tensile shear force and the maximum displacement were utilized to characterize the performance of the welding processes. The nugget diameter has been measured to create a clear definition of the RSW physical properties. The experimental results show that the tensile shear load bearing capacity is bond to increase as the electrode pressure increases based on a value in both the welding currents and the decrease at the higher values. The low current value at low and at the highest electrode pressures; during the high current value which could be at the middle of the electrode pressure values it can exhibit the superior mechanical properties. The effect of this electrode pressure on the tensile shear load bearing capacity is bond to increase as the welding current increases as well. This, also been assessed and examined based on the low carbon content.

The Effects of the Welding Parameters on Tensile Properties of RSW Junctions of DP1000 Sheet Steel

In this study, the maximum tensile shear load bearing capacity of the resistance spot welded DP1000 steel was measured and the tensile shear properties of the joints were evaluated. The effects of different welding parameters on microstructure, microhardness and tensile shear properties were investigated. Weld processes were performed by using 5kA and 7kA weld currents and 2-6bar electrode pressures. The microstructure of the welded materials was evaluated and the hardness profiles were determined. Experimental results showed that increasing electrode pressure and weld current increased the tensile shear load bearing capacity. It was also observed that the expulsion had a negative effect on the tensile shear load bearing capacity.

Effect of Electrode Materials Type on Resistance Spot Welding of AISI 430 Ferritic Stainless Steel

In this study, AISI 430 ferritic stainless steel sheet with 0.6 mm thickness was joined by resistance spot welding using different electrode materials. The effects of electrode materials and welding parameters on the mechanical properties of welded samples are defined in terms of peak load. The hardness and tensile shear load bearing capacity of welded joint was determined and the microstructure of welded samples was also evaluated. The most suitable welding parameters for each electrode material were determined.

Combined effect of resistance spot welding and precipitation hardening on tensile shear load bearing capacity of A286 superalloy

This work aims to study the combined effect of resistance spot welding (RSW) and precipitation hardening on tensile shear load bearing capacity (TSLBC) of A286 superalloy. The tensile shear test specimens were welded in the solution treated condition, and then subjected to different precipitation hardening treatments. The impoverishment in Ti, due to its segregation towards the interdendritic region (studied by performing SEM/EDX analysis), causes the development of gamma prime depleted zones in the dendrite core of the weld nugget, which is associated with a decrease of the mechanical properties with respect to the base metal. The segregation of Ti towards the interdendritic region of the weld nugget has also influence on the eta phase formation, which appears later (with longer aging times) in the weld nugget than in the base metal. The aging time at which the maximum experimental TSLBC is reached is, for both aging temperatures, 100h. The experimental TSLBC of the tensile shear test specimens hardened at lower aging temperature is greater (except for the shortest aging time) than that of those hardened at higher aging temperature.

Quality assessment of resistance spot welding joints of AISI 304 stainless steel based on elastic nets

In this work, the quality of resistance spot welding (RSW) joints of 304 austenitic stainless steel (SS) is assessed from its tensile shear load bearing capacity (TSLBC). A predictive model using a polynomial expansion of the relevant welding parameters, i.e. welding current (WC), welding time (WT) and electrode force (EF) and elastic net regularization is proposed. The predictive power of the elastic net approach has been compared to artificial neural networks (ANNs), previously used to predict TSLBC, and smoothing splines in the framework of a generalized additive model. The results show that the predictive and classification error of the elastic net model are statistically comparable to benchmarks of the best pattern recognition tools whereas it overcomes correlation problems and performs variable selection at the same time, resulting in a simpler and more interpretable model. These features make the elastic net model amenable to be used in the design of welding conditions and in the control of manufacturing processes.

Microstructure and mechanical properties evolution of friction stir spot welded high-Mn twinning-induced plasticity steel

Friction stir spot welding of high-Mn twinning-induced plasticity steel was studied. Welds were made at different tool rotation speeds and constant plunge rate and dwell time. The microstructure evolution was examined by optical microscopy, scanning electron microscopy and electron backscattered diffraction technique. In addition, the microhardness distribution and tensile-shear load bearing capacity were measured. The friction stir spot welding process successfully produced high integrity completely defect-free joints at all the proposed welding parameters. However, the complex plastic deformation and high thermal cycle experienced had a significant effect on the weld region, which consisted of three distinct zones. The flow transition zone, stir zone and torsion zone were all characterized by a recrystallized grain structure. The heat affected zone was characterized by a coarse grain structure as a result of grain growth caused by the high thermal cycles experienced. The hardness was significantly affected by friction stir spot welding, resulting in a softened region in the joint area. The softening increased as the rotation rate increased. The maximum peak tensile shear load of 13kN was obtained at 750rpm, and a considerable amount of extension was obtained in all the joints with a maximum of 4mm at 500rpm.

Influence of Welding Parameters on the Quality of Resistance Spot Welded Joints of DP600 Steels

Advanced high-strength dual-phase steel was developed specifically for automotive industry in order to benefit from its excellent formability and great crash absorption ability in comparison with conventional AHSS. Resistance spot welding is the dominant and effective method of joining metal sheets in automobile industry. After spot welding, important changes occur in mechanical and metallurgical properties of the spot welded areas and heat affected zones. The investigation into these changes is very important for safety, which depends on the strength of the welded joints. Weldability of the DP steel is one of the key factors governing its application in automotive industry. The influence of the primary welding parameters, especially welding current, on the weld quality was investigated by testing microhardness and tensile shear load bearing capacity of resistance spot welds of DP600 steel sheets.

The microstructural evolution and mechanical properties of resistance spot welded Fe–31Mn–3Al–3Si TWIP steel

In this study, similar resistance spot weldability of an Fe–31Mn–3Al–3Si Twinning Induced Plasticity (TWIP) steel was investigated. The microstructural evolution was studied by means of optical microscopy (OM) and scanning electron microscopy (SEM) in order to evaluate the effects of experimental conditions on spot welded (RSW) joints. In addition, tensile–shear load bearing capacity of welded materials and failure modes were precisely inspected to determine the mechanical properties and fracture behavior of welded joints. The results illustrated that due to the expulsion phenomenon, optimum welding parameters for the experimental TWIP steel are shifted to lower values. Meanwhile, OM indicated that the fusion zone (FZ) held a dendritic structure; however, heat affected zone (HAZ) exhibited a significant grain growth in the narrow band. At upper welding parameters, shrinkage cavities and, in certain specimens, in microscopic scale inter-dendritic micro-pores were observed.

Effect of Welding Current and Time on the Microstructure, Mechanical Characterizations, and Fracture Studies of Resistance Spot Welding Joints of AISI 316L Austenitic Stainless Steel

This article aims at investigating the effect of welding parameters, namely, welding current and welding time, on resistance spot welding (RSW) of the AISI 316L austenitic stainless steel sheets. The influence of welding current and welding time on the weld properties including the weld nugget diameter or fusion zone, tensile-shear load-bearing capacity of welded materials, failure modes, energy absorption, and microstructure of welded nuggets was precisely considered. Microstructural studies and mechanical properties showed that the region between interfacial to pullout mode transition and expulsion limit is defined as the optimum welding condition. Electron microscopic studies indicated different types of delta ferrite in welded nuggets including skeletal, acicular, and lathy delta ferrite morphologies as a result of nonequilibrium phases, which can be attributed to a fast cooling rate in the RSW process. These morphologies were explained based on Shaeffler, WRC-1992, and pseudo-binary phase diagrams. The optimum microstructure and mechanical properties were achieved with 8-kA welding current and 4-cycle welding time in which maximum tensile-shear load-bearing capacity or peak load of the welded materials was obtained at 8070 N, and the failure mode took place as button pullout with tearing from the base metal. Finally, fracture surface studies indicated that elongated dimples appeared on the surface as a result of ductile fracture in the sample welded in the optimum welding condition.

Resistance spot welding joints of AISI 316L austenitic stainless steel sheets: Phase transformations, mechanical properties and microstructure characterizations

In this paper, we aim to optimize welding parameters namely welding current and time in resistance spot welding (RSW) of the austenitic stainless steel sheets grade AISI 316L. Afterward, effect of optimum welding parameters on the resistance spot welding properties and microstructure of AISI 316L austenitic stainless steel sheets has been investigated. Effect of welding current at constant welding time was considered on the weld properties such as weld nugget size, tensile–shear load bearing capacity of welded materials, failure modes, failure energy, ductility, and microstructure of weld nuggets as well. Phase transformations that took place during weld thermal cycle were analyzed in more details including metallographic studies of welding of the austenitic stainless steels. Metallographic images, mechanical properties, electron microscopy photographs and micro-hardness measurements showed that the region between interfacial to pullout mode transition and expulsion limit is defined as the optimum welding condition. Backscattered electron scanning microscopic images (BE-SEM) showed various types of delta ferrite in weld nuggets. Three delta ferrite morphologies consist of skeletal, acicular and lathy delta ferrite morphologies formed in resistance spot welded regions as a result of non-equilibrium phases which can be attributed to the fast cooling rate in RSW process and consequently, prediction and explanation of the obtained morphologies based on Schaeffler, WRC-1992 and Pseudo-binary phase diagrams would be a difficult task.

Effect of Stretching during Welding Process on the Weldability of Dissimillar Metals Resistance Spot Welded between Carbon Steel and Low Nickel Stainless Steel

Due to the local heating of welding, deformation will occur on the welding structure. To mitigate this deformation, the method called stretching technology was proposed by previous study. In this method, plate was stretched to certain pre-strain, kept in this condition and then welded to another sheet. It can reduce the welding deformation significantly. However, pre-strain will change the properties of joined materials and lead different behavior of welded materials. It will be complicated if dissimilar metals are welded due to different physical and metallurgical properties. Carbon steel SS400 with the thickness of 3.0 mm and 1.0 mm thick-low nickel stainless steel were welded using resistance spot welding (RSW) process with constant electrode pressure and weld time of 6 kN and 5 second respectively. During welding process, low nickel stainless steel was stretched in four different levels pre-strain of 0%, 1%, 1.5% and 2%. Welding current were varied in the range from 3.02 to 4.20 kA. Microstructure investigations and tensile-shear tests were conducted to evaluate the weldability of RSW joint. Generally, stretching during welding process decreased the fussion zone area of RSW joint. In the low welding current, there is no fussion in the interface of stretched plate, but fussion still occured in the interface of unstretched plate. In all levels of welding current, stretching during welding decreased fussion zone area and led to decrease tensile-shear load bearing capacity of RSW joint.