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resistance-spot-welding
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Simulation of welding residual stresses in resistance spot welding, FE modeling and X-ray verification
, Article Journal of Materials Processing Technology ; Volume 205, Issue 1-3 , 26 August , 2008 , Pages 60-69 ; 09240136 (ISSN) ; Serajzadeh, S ; Kokabi, A. H ; Sharif University of Technology
2008
Abstract
In the present study, an electro-thermo-mechanical model is utilized to predict electrical potential, temperature and residual stress distributions during different stages of resistance spot welding. In order to improve accuracy, material properties including physical, thermal and mechanical properties supposed to be temperature-dependent. The employed model is capable of considering the effects of welding parameters such as heat input and welding time on residual stress distribution. The model results are then compared with the measured residual stresses and good agreement is observed. Predictions show that maximum tensile residual stresses are located at the weld center while they are...
Effect of weld nugget size on overload failure mode of resistance spot welds
, Article Science and Technology of Welding and Joining ; Volume 12, Issue 3 , 2007 , Pages 217-225 ; 13621718 (ISSN) ; Asgari, H. R ; Mosavizadch, S. M ; Hoveida Marashi, P ; Goodarzi, M ; Sharif University of Technology
2007
Abstract
In the present paper, effects of welding current, welding time, electrode pressure and holding time on the weld nugget size were studied. A failure mechanism was proposed to describe both interfacial and pullout failure modes. This mechanism was confirmed by SEM investigations. In the light of this mechanism, the effect of welding parameters on static weld strength and failure mode was studied. Then, an analytical model was proposed to predict failure mode and to estimate minimum nugget diameter (critical diameter) to ensure pullout failure mode in shear tensile test. On the contrary to existing industrial standards, in this model, critical nugget diameter is attributed to metallurgical...
Critical assessment: dissimilar resistance spot welding of aluminium/steel: challenges and opportunities
, Article Materials Science and Technology (United Kingdom) ; Volume 33, Issue 15 , 2017 , Pages 1705-1712 ; 02670836 (ISSN) ; Sharif University of Technology
Abstract
Dissimilar joining of aluminium and steel, especially using resistance spot welding as a critical process in vehicle manufacturing, is a key challenge for multi-materials lightweight design strategy. Controlling the formation and growth of Al5Fe2 intermetallic is the outstanding issue for producing high strength crash-resistance Al/steel dissimilar resistance spot welds. This critical assessment highlights the current understating regarding factors affecting the joint properties and approaches to control the interfacial reaction. Finally, the unresolved scientific challenges are discussed with the goal of shedding light on the path forward to produce reliable metallurgical bonding between...
Peak load and energy absorption of DP600 advanced steel resistance spot welds
, Article Ironmaking and Steelmaking ; Volume 44, Issue 9 , 2017 , Pages 699-706 ; 03019233 (ISSN) ; Pouranvari, M ; Salim, R. K ; Hashim, F. A ; Marashi, S. P. H ; Sharif University of Technology
Abstract
The paper aims at investigating the microstructure, failure mode transition, peak load and energy absorption of DP600 dual phase steel during the tensile-shear test. It was found that the welding current has profound effect on the load–displacement characteristics. In the low welding current, welds failed in interfacial failure mode. Increasing welding current resulted in sufficient weld nugget growth to promote double-sided pullout failure mode with improved mechanical properties. Further increase in the welding current caused expulsion and failure mode was changed to single-sided pullout with reduced energy absorption capability. It was found that the fusion zone size is the key parameter...
A pathway to produce strong and tough martensitic stainless steels resistance spot welds
, Article Science and Technology of Welding and Joining ; Volume 24, Issue 3 , 2019 , Pages 185-192 ; 13621718 (ISSN) ; Pouranvari, M ; Sharif University of Technology
Taylor and Francis Ltd
2019
Abstract
Martensitic stainless steel (MSS) resistance spot welds are prone to quasi-cleavage interfacial failure with very low energy absorption capability due to formation of hard and brittle carbon and chromium rich martensite in the fusion zone (FZ). In this work, a new pathway is proposed to enhance strength/toughness of the MSS resistance spot welds based on modification of the FZ composition/microstructure via introducing a nickel interlayer. This altered the FZ microstructure from dual phase microstructure of martensite and δ-ferrite to austenitic microstructure with finely dispersed ultra-fine chromium rich carbides. Formation of a tough predominately austenitic microstructure in the FZ...
Prediction of the failure mode of automotive steels resistance spot welds
, Article Science and Technology of Welding and Joining ; Volume 25, Issue 6 , 2020 , Pages 511-517 ; Jaderian, S ; Mazaheri, Y ; Pouranvari, M ; Sharif University of Technology
Taylor and Francis Ltd
2020
Abstract
In this study, the critical nugget size, at which the failure state in tensile shear test changed from the interfacial failure mode to the pull-out failure one, was estimated as a function of nugget and base metal hardness. The proposed approach could address the effect of various parameters involved in resistance spot welding process, such as sheet thickness, base metal chemical composition and physical properties of electrodes and sheets. The reliability of the present model was evaluated using independent experimental results. Based on the obtained results, the effect of steel composition on critical nugget diameter was found to be more important, especially for the sheets thicker than...
Pathways to improve the austenite–ferrite phase balance during resistance spot welding of duplex stainless steels
, Article Science and Technology of Welding and Joining ; Volume 24, Issue 1 , 2019 , Pages 8-15 ; 13621718 (ISSN) ; Pouranvari, M ; Movahedi, M ; Sharif University of Technology
Taylor and Francis Ltd
2019
, M.Sc. Thesis Sharif University of Technology ; Kazeminezhad, Mohsen (Supervisor) ; Kokabi, Amirhossein (Supervisor)
Abstract
Considering that automobile weigth reduction in industry is important, improvement the strength of low carbon steel sheets is important. These sheets can be supported the service condition in lower thicknesses. Bulk nano-structured materials have been mostly attracted in materials science due to their unique physical and mechanical properties. Severe plastic deformation (SPD) is one of the most efficient methods to produce ultra fine grained or nano-structured materials. Materials produced by SPD are of great importance because of (1) non-porous structure, (2) great mechanical properties such as high strength and toughness and (3) proper dimension for mechanical and physical testing. ...
, M.Sc. Thesis Sharif University of Technology ; Karimi Taheri, Ali (Supervisor)
Abstract
This study was conducted in order to investigate the effect of difference in electrical resistivity between low carbon steel and austenitic stainless steel on the physical and mechanical properties and fracture mode of dissimilar resistance spot welds of these alloys. For this purpose, plastic deformation using constrained groove pressing combined with rolling applied to low carbon steel in three levels of 40%, 156% and 272%. Microstructural characterization, micro-hardness measurements and shear-tension test were performed. It was shown that by increasing the pre-strain in low carbon steel its electrical resistivity increases from 13.08 μΩ.cm to 19.5 μΩ.cm and because of reduction of...
Effect of Different Defects of Spot Welded Joint in Automotive Body on Fatigue Strength: Experimental and Numerical Investigation
, M.Sc. Thesis Sharif University of Technology ; Farrahi, Gholamhossein (Supervisor) ; Mehmanparast, Ali (Supervisor) ; Reza Kashyzadeh, Kazem (Co-Supervisor)
Abstract
On average there are to resistance spot welding connections per vehicle. The quality of these welding directly affects the quality of the finished product and the strength of the vehicle against various loads, including road roughness, different maneuvers and even sudden impacts from accidents. During the spot welding process, unintentional failures occur due to the wrong choice of current, force and time. The aim of this study is to investigate the fatigue strength of three-sheets welding joints in numerical and laboratory methods, considering the defects of (Undersize weld, Stick, edge of sheet metal and Edge of sheet metal-SECANT) . For this purpose, a healthy spot welding model was first...
Studying of Micro-structure and Mechanical Properties of Resistant Spot Welds of Nickel Base Super Alloys
, M.Sc. Thesis Sharif University of Technology ; Pouranvari, Majid (Supervisor)
Abstract
Resistance spot welding is one of the fabrication processes of gas turbines. Due to few published works about using RSW for joining participation hardened nickel base super alloys like Nimonic C263 and solid solution hardened ones like Hastelloy X, this work tries to investigate the microstructure and mechanical properties of RSW joints of these super alloys. In phase one, effect of welding current on structural properties of welds, hardness profile from the center of the weld to the edge of it, failure mod and failure energy were investigated. In phase two, effect of standard heat treatment of Nimonic C263 and the initial microstructure of the base metal on the micro-structure and...
Reliability of Ultrasonic Technique Used for Defect Detection of Spot Welded Plates in Automotive Industry
, M.Sc. Thesis Sharif University of Technology ; Farrahi, Gholamhossien (Supervisor) ; Chizari, Mahmoud (Supervisor) ; kashizadeh, Kazem Reza (Co-Supervisor)
Abstract
Resistance Spot Welding (RSW) is one of the common techniques for connecting steel sheets in automotive industries. There are about 3000-5000 RSWs in the automotive chassis and body. Therefore, health and quality of RSW play a critical role in the final product performance. Also, welding process should be performed in a fully controlled program to ensure the durability of the vehicle body. In the automotive industry, there are various non-destructive methods (i.e., Chisel and Ultrasonic tests) and peel test as a destructive test (DT) to control the quality of RSW. Since the DT method is costly (waste of time, manpower, and materials), the main aim of the present research is to evaluate the...
Effect of expulsion on peak load and energy absorption of low carbon steel resistance spot welds
, Article Science and Technology of Welding and Joining ; Volume 13, Issue 1 , 2008 , Pages 39-43 ; 13621718 (ISSN) ; Abedi, A ; Marashi, P ; Goodarzi, M ; Sharif University of Technology
2008
Abstract
The effects of weld nugget size and expulsion on the performance of low carbon steel resistance spot weld have been investigated in the present paper. Failure mode, peak load and failure energy obtained in tensile-shear test have been used to describe the performance of spot weld. The influence of voids and porosity as well as electrode indentation associated with expulsion on peak load and failure energy is discussed. The results showed that although expulsion does not reduce the load carrying capacity of spot welds, it decreases their energy absorption capability which was attributed to the change of failure location due to excessive electrode indentation associated with expulsion. © 2008...
Fatigue life estimation of spot welds using a crack propagation-based method with consideration of residual stresses effect
, Article Materials Science and Engineering A ; Volume 527, Issue 23 , 2010 , Pages 6359-6363 ; 09215093 (ISSN) ; Kokabi, A. H ; Sharif University of Technology
2010
Abstract
In the present paper, a crack propagation-based fatigue life estimation approach has been proposed for resistance spot welds. The presented approach also takes into account the effect of welding residual stresses. It can provide an accurate and systematic prediction of the life of spot weld joints with various dimensions and shapes. Experimental verification tests confirmed the validity of the calculations and good agreement was found between the theoretical predictions and experimental data
Peak load and energy absorption of DP600 advanced steel resistance spot welds
, Article Ironmaking and Steelmaking ; 2016 , Pages 1-8 ; 03019233 (ISSN) ; Pouranvari, M ; Salim, R. K ; Hashim, F. A ; Hoveida Marashi, S. P ; Sharif University of Technology
Taylor and Francis Ltd
2016
Abstract
The paper aims at investigating the microstructure, failure mode transition, peak load and energy absorption of DP600 dual phase steel during the tensile-shear test. It was found that the welding current has profound effect on the load–displacement characteristics. In the low welding current, welds failed in interfacial failure mode. Increasing welding current resulted in sufficient weld nugget growth to promote double-sided pullout failure mode with improved mechanical properties. Further increase in the welding current caused expulsion and failure mode was changed to single-sided pullout with reduced energy absorption capability. It was found that the fusion zone size is the key parameter...
Role of zinc layer in resistance spot welding of aluminium to steel
, Article Materials and Design ; Volume 102 , 2016 , Pages 106-114 ; 02641275 (ISSN) ; Movahedi, M ; Kokabi, A. H ; Sharif University of Technology
Elsevier Ltd
2016
Abstract
Effects of zinc layer on microstructure and mechanical behavior of resistance spot welds of aluminum to galvanized (GS-Al joint) and low carbon steel (PS-Al joint) were explored. The results showed that although nugget 'volume' in PS-Al joint was larger, the nugget 'diameters' of PS-Al and GS-Al joints were almost the same in size since the melted zinc layer was pushed toward the outer regions of the nugget. Melting and evaporation of zinc coat led to reduction of Al-Fe intermetallic layer thickness. Presence of zinc also reduced the fixture-induced tensile stress. Utilizing carbon steel fixtures during welding caused a sensible vibration in the joint members. The vibration resulted in...
Ferritic-austenitic stainless steels dissimilar resistance spot welds: Metallurgical and failure characteristics
, Article Science and Technology of Welding and Joining ; Volume 21, Issue 6 , 2016 , Pages 438-445 ; 13621718 (ISSN) ; Khorramifar, M ; Hoveida Marashi, S. P ; Sharif University of Technology
Taylor and Francis Ltd
2016
Abstract
The paper addresses the microstructure and failure characteristics of dissimilar resistance spot welds between austenitic stainless steel and ferritic stainless steel. The fusion zone (FZ) of dissimilar welds exhibited complex microstructure consisting of ferrite, austenite and martensite. The development of this triplex structure in the FZ was explained by analysing the phase transformation path and austenite stability. Results showed that all dissimilar welds failed in partial thickness-partial pull-out failure mode. It was shown that the fraction of the nugget fracture of the weld is reduced by increasing the FZ size improving the mechanical performance of the weld. Peak load and energy...
Understanding the factors controlling the interfacial failure strength of advanced high-strength steel resistance spot welds: hardness vs. fracture toughness
, Article Science and Technology of Welding and Joining ; Volume 23, Issue 6 , 2018 , Pages 520-526 ; 13621718 (ISSN) ; Sharif University of Technology
Taylor and Francis Ltd
2018
Abstract
The failure of advanced high-strength steels’ spot welds is a critical issue for automotive crashworthiness. This paper deals with understanding the underlying factors of the tensile-shear strength of automotive steels’ resistance spot welds during interfacial failure. It was found that the ratio of the fracture toughness to the hardness of the fusion zone is the critical factor governing the interfacial failure mechanism: ductile shear failure (controlled by the fusion zone hardness) vs. cleavage crack propagation (controlled by the fracture toughness). This clarification could pave the way for more accurate modelling of interfacial failure of advanced steel resistance spot welds and shed...
Mechanical properties of martensitic stainless steel weld/adhesive hybrid bonds
, Article Science and Technology of Welding and Joining ; Volume 23, Issue 3 , 2018 , Pages 227-233 ; 13621718 (ISSN) ; Safikhani, E ; Sharif University of Technology
Taylor and Francis Ltd
2018
Abstract
Hybrid weld-adhesive bonding (AB) was used as an approach to improve the mechanical properties of martensitic stainless steel resistance spot welds. The weld fusion zone in both techniques was composed of predominantly martensite and δ-ferrite. It was found that the presence of adhesive does not induce excess hardening effect in the fusion zone. It was shown that hybrid AB/resistance spot welding) i.e. weld-bonding) technique can double the peak load and energy absorption of the joints compared to those of the resistance spot welds. To obtain high performance weld-bonded joints, heat generation during welding should be controlled to produce weld bonds with large fusion zone size, but without...
Enhanced mechanical properties of martensitic stainless steels resistance spot welds enabled by in situ rapid tempering
, Article Science and Technology of Welding and Joining ; Volume 25, Issue 2 , 2020 , Pages 119-126 ; Aghajani, H ; Ghasemi, A ; Sharif University of Technology
Taylor and Francis Ltd
2020
Abstract
Resistance spot weldability of martensitic stainless steels is impaired by the formation of brittle martensite in the fusion zone (FZ). In this paper, in situ rapid tempering via applying a second pulse current after a first melting/solidification pulse during resistance spot welding of AISI 420 martensitic stainless steel sheets was used as a pathway to enhance the toughness of the FZ. By using proper second pulse conditions, the FZ with reduced hardness can be generated which is featured by a decomposed martensitic structure with nano-sized carbide precipitations. The improved toughness as a consequence of this modified microstructure resulted in remarkable enhancement of the peak load and...