Download or read book Towards Understanding the Effects of Current Input on Fatigue Mechanisms in Resistance Spot Welding of Advanced High Strength Steels written by Conner Cleek and published by . This book was released on 2020 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In this study, the relationship of welding parameters to fatigue mechanisms is examined in spot welding of advanced high strength steels. Lightweighting efforts in the automotive industry are part of a push for greater fuel economy and improved consumer safety. TBF-1180 is an advanced high strength steel being developed for use in structurally critical components, however its fatigue behavior is not well understood. Electro galvanized TBF-1180 possesses corrosion resistant properties, however the additional zinc layer allows for the possibility of zinc-penetrative liquid metal embrittlement (LME) to occur during resistance spot welding (RSW). Additionally, variations in weld input and correspondingly heat input can affect the performance of welds due to microstructural changes that occur. In this study, the effect of LME and changes in microstructure were assessed in separate experiments for their fatigue impact in TBF-1180. Welds were fabricated in a traditional lap shear geometry in order to investigate the effects of LME, while an hourglass shaped cap geometry was used for welds with microstructural variation. Fatigue testing revealed that for lap-shear coupons containing LME cracks, no deleterious effect was observed. Cap geometry specimens were assessed for performance in a control and a high-current low-time condition, and a significant fatigue knockdown factor was found. Post-mortem fractography on both specimen geometries revealed that fatigue cracks initiated at the inner faying surface, regardless of the presence of LME. Finite element analysis confirmed that the LME cracks in the lap shear weld experience compressive stresses during loading, contributing to the lack of fatigue impact. Experimental conditions used for the cap geometry had lower heat input, which can result in less retained metastable austenite after welding, leading to reduced crack growth resistance. To tests the hypothesis that less retained metastable austenite after welding can cause a reduction in the number of cycles to failure in the spot weld, life prediction were made using fracture mechanics concepts coupled with reported knockdown factors on crack growth rates in relation to the amount of transformed martensite. The life predictions generated with this method strongly matched the observed fatigue behavior for the cap geometry specimens.

Download or read book Effect of Surface Condition on Resistance Spot Welding of Advanced High Strength Steel written by Xu Han and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Advanced high strength automotive sheet steel (AHSS) is used in body-in-white design to reduce vehicle weight while maintaining high crashworthiness. Surface coatings applied to AHSS to protect it from oxidation and decarburization during its processing and life cycle. Due to the characteristics of AHSS, including alloying content and thermal process requirements, a variation of final surface conditions is possible. The resistance welding process is affected by surface changes as it alters the electrical contact resistance. As a result, a change in resistance spot welding process window occurs. Without proper attention, this variation in the operation window could reduce the joint strength and results in an unpredictable failure by having an undersized nugget. In this study, two surface-related phenomena, internal oxidation, and zinc diffusion, were investigated to characterize their impact on resistance spot welding. Additionally, a heat input based electrical dynamic resistance approach was proposed to determine appropriate welding current given variations in the Zn diffusion layer resulting from heat treating during this hot stamping process for PHS steels. Promotion of internal oxidation is used in Zn galvanizing line to improve the wettability of the steel surface to the Zn pool via the enhancement of the reactive wetting. The presence of these internal oxides has shown to shift the weld lobe to higher currents, increasing the time required to generate an acceptable weld. Study of weld development showed that surface melting is responsible for this shift in the weld process window. The surface melting created a liquid contact surface between the faying surface, which reduced the electric contact resistance and heat generation at the weld faying surface. A smaller nugget was formed due to the reduction of heating. To compensate for this reduced heat generation, a higher welding current was required when RSW of internally oxidized samples. Zinc diffusion from the galvannealed coating to the steel substrate occurs when a galvannealed steel was exposed to elevated temperature during heat treatment in the press-hardening process. This formed a Fe-Zn diffusion layer. The thickness and composition of the diffusion layer were found to be dependent on heat-treatment conditions. With an increase in heat-treatment time, the electrical resistance of the steel sheet was observed to increase as well. With higher electrical resistance, less welding current was needed to weld the material. While a change in nugget size occurred when welding steels made using different heat-treatment conditions with constant welding parameters, the mechanical lap shear strength was not impacted. Martensite tempering in the heat-affected region was more severe in samples with a larger diameter weld nugget, which decreased the required stress for failure to occur, counter-acting the increase in strength gained from the larger nugget size. This work has shown that with a heat-treatment time ranging between 4 to 10 minutes, a robust resistance welding schedule can be determined to generate a mechanically sound weld. Dynamic electrical resistance has been used to monitor the weld quality. Heat input analysis was shown to reflect the weld development as it takes into account the full weld cycle. Heat input has shown to have a linear correlation with nugget size. Undersized nugget can be successfully detected and corrected by changing the welding current based on the heat input value calculated from dynamic resistance measurement.

Download or read book Failure Mechanisms of Advanced Welding Processes written by X Sun and published by Elsevier. This book was released on 2010-07-15 with total page 331 pages. Available in PDF, EPUB and Kindle. Book excerpt: Many new, or relatively new, welding processes such as friction stir welding, resistance spot welding and laser welding are being increasingly adopted to replace or improve on traditional welding techniques. Before advanced welding techniques are employed, their potential failure mechanisms should be well understood and their suitability for welding particular metals and alloys in different situations should be assessed. Failure mechanisms of advanced welding processes provides a critical analysis of advanced welding techniques and their potential failure mechanisms. The book contains chapters on the following topics: Mechanics modelling of spot welds under general loading conditions and applications to fatigue life predictions, Resistance spot weld failure mode and weld performance for aluminium alloys, dual phase steels and TRIP steels, Fatigue behaviour of spot welded joints in steel sheets, Non-destructive evaluation of spot weld quality, Solid state joining - fundamentals of friction stir welding, Failure mechanisms in friction stir welds, Microstructure characteristics and mechanical properties of laser weld bonding of magnesium alloy to aluminium alloy, Fatigue in laser welds, Weld metal ductility and its influence on formability of tailor welded blanks, Joining of lightweight materials using reactive nanofoils, and Fatigue life prediction and improvements for MIG welded advanced high strength steel weldments. With its distinguished editor and international team of contributors, Failure mechanisms of advanced welding processes is a standard reference text for anyone working in welding and the automotive, shipbuilding, oil and gas and other metal fabrication industries who use modern and advanced welding processes. Provides a critical analysis of advanced welding techniques and their potential failure mechanisms Experts in the field survey a range of welding processes and examine reactions under various types of loading conditions Examines the current state of fatigue life prediction of welded materials and structures in the context of spot welded joints and non-destructive evaluation of quality

Download or read book Resistance and Ultrasonic Spot Welding of Light weight Metals written by Ying Lu (Ph. D. in welding engineering) and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Multi-materials vehicle structures, employing light-weight metals such as advanced high strength steels (AHSS), aluminum alloys, can satisfy the ever-increasing requirement of light-weighting and fuel efficiency, as well as maintaining or improving the crash resistance of vehicles. The present research provides a fundamental understanding of the process-microstructure-mechanical properties of resistance and ultrasonic spot welding of light-weight metals. The dissertation consists of three main parts: (1) study of the relationship of process-microstructure-mechanical properties for resistance spot welded two sheets (2T) and complex stack-ups of ultra-high strength grade of AHSS, (2) development of a novel technique, namely Ultrasonic Plus Resistance Spot Welding, for dissimilar metal joining of Al to steel, and (3) investigation of the bonding mechanism of USW of Al by in-situ relative vibration measurement. In the first part, softening in subcritical heat affected zone of resistance spot welded hot-stamped boron steels is investigated by weld microstructure characterization and tempering kinetics of martensite. The local constitutive behavior of the potential failure locations is extracted and incorporated into performance model to investigate its effect on the accuracy of deformation and failure prediction. A major challenge for RSW of complex stack-ups with large thickness ratio is the limited nugget penetration into the thin sheet at the outside of the stack-up. The effect of welding current, electrode force, electrode material/size on nugget formation and the possible ways to improve nugget penetration into the thin sheet are investigated for 3T and 4T stack-ups of AHSS. The second part of the dissertation is focused on the development of a new dissimilar metal joining method, namely ultrasonic plus resistance spot welding (abbreviated as U+RSW) for Al/Steel. The bonding mechanisms have been investigated through numerical simulation to validate the concept. The third and last part of the dissertation is to understand the bonding mechanism in USW. Particularly, the relative motion of the sonotrode, aluminum specimens, and anvil in USW is investigated using an in-situ velocity measurement technique, Photonic Doppler Velocimetry (PDV). The relative motion analysis is correlated to destructive testing results, including lap-shear tensile testing and weld microstructure characterization, to understand and quantify bond formation during USW. In summary, the present research studies the process-microstructure-property relationships of resistance spot welding of AHSS, dissimilar metal welding of Al to steel, and ultrasonic spot welding of Al. An improved fundamental understanding is developed for (1) heat conduction, electric current flow, mechanical stress and deformation, and nugget formation in 2T and complex stack-ups of resistance spot welded ultra-high strength steel, (2) tempering kinetics of martensite and SCHAZ softening, (3) microstructure-specific constitutive behaviors, (4) weldability, intermetallics, and strength of dissimilar metal joint between Al and steel in U+RSW, and (5) bonding mechanism in USW. Such new knowledge is essential to ensure sound multi-materials vehicle structures employing various light-weight metals to satisfy the ever-increasing demand for fuel efficiency and crash resistance.

Download or read book Fatigue in Friction Stir Welding written by J. Brian Jordon and published by Butterworth-Heinemann. This book was released on 2019-02-27 with total page 198 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fatigue in Friction Stir Welding provides knowledge on how to design and fabricate high performance, fatigue resistance FSW joints. It summarizes fatigue characterizations of key FSW configurations, including butt and lap-shear joints. The book's main focus is on fatigue of aluminum alloys, but discussions of magnesium, steel, and titanium alloys are also included. The FSW process-structure-fatigue performance relationships, including tool rotation, travel speeds, and pin tools are covered, along with sections on extreme fatigue conditions and environments, including multiaxial, variable amplitude, and corrosion effects on fatigue of the FSW. From a practical design perspective, appropriate fatigue design guidelines, including engineering and microstructure-sensitive modeling approaches are discussed. Finally, an appendix with numerous representative fatigue curves for design and reference purposes completes the work. - Provides a comprehensive characterization of fatigue behavior for various FSW joints and alloy combinations, along with an in-depth presentation on crack initiation and growth mechanisms - Presents the relationships between process parameters and fatigue behavior - Discusses modeling strategies and design recommendations, along with experimental data for reference purposes

Download or read book Resistance Spot Welding of Advanced High Strength Steels written by and published by . This book was released on 2019 with total page 159 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Advanced Materials ICAMMP 2011 written by Jing Long Bu and published by Trans Tech Publications Ltd. This book was released on 2011-12-06 with total page 2520 pages. Available in PDF, EPUB and Kindle. Book excerpt: These volumes comprise papers, on the topic of “Advanced Materials”, selected from the second International Conference on Advances in Materials and Manufacturing (ICAMMP 2011) held on the 16-18th December 2011 in Guilin, China. The 468 peer-reviewed papers are grouped into the chapters: 1: Composites, 2: Micro / Nano Materials, 3: Iron and Steel, 4: Ceramic, 5: Metal Alloy Materials, 6: Biomaterials, 7: Optical/Electronic/Magnetic Materials, 8: Building Materials, 9: New Energy Materials and Environmental Materials, 10: Biomaterials and Chemical Materials, 11: Thin Films, 12: New Functional Materials, 13: Materials and Design.

Download or read book Resistance Welding written by Hongyan Zhang and published by CRC Press. This book was released on 2011-12-13 with total page 465 pages. Available in PDF, EPUB and Kindle. Book excerpt: Drawing on state-of-the-art research results, Resistance Welding: Fundamentals and Applications, Second Edition systematically presents fundamental aspects of important processes in resistance welding and discusses their implications on real-world welding applications. This updated edition describes progress made in resistance welding research and

Download or read book Fatigue Performance of Welded High Strength Steels written by Welding Institute and published by . This book was released on 1974 with total page 204 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Fatigue Analysis of Welded Components written by E. Niemi and published by Woodhead Publishing. This book was released on 2006-09-27 with total page 56 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report provides background and guidance on the use of the structural hot spot stress approach to the fatigue design of welded components and structures. It complements the IIW recommendations for 'Fatigue Design of Welded Joints and Components' and extends the information provided in the IIW recommendations on 'Stress Determination for Fatigue Analysis of Welded Components'. This approach is applicable to cases of potential fatigue cracking from the weld toe. It has been in use for many years in the context of tubular joints. The present report concentrates on its extension to structures fabricated from plates and non-tubular sections.Following an explanation of the structural hot spot stress, its definition and its relevance to fatigue, the authors describe methods for its determination. Stress determination from both finite element analysis and strain gauge measurements is considered. Parametric formulae for calculating stress increases due to misalignment and structural discontinuities are also presented. Special attention is paid to the use of finite element stress analysis and guidance is given on the choice of element type and size for use with either solid or shell elements. Design S-N curves for use with the structural hot spot stress are presented for a range of weld details. Finally, practical application of the recommendations is illustrated in two case studies involving the fatigue assessment of welded structures using the structural hot spot stress approach. - Provides practical guidance on the application of the structural hot-spot stress approach - Discusses stress determination from both finite element analysis and strain gauge measurements - Practical application of the recommendations is illustrated in two case studies

Download or read book Microstructure and Texture in Steels written by Arunansu Haldar and published by Springer Science & Business Media. This book was released on 2009-09-03 with total page 484 pages. Available in PDF, EPUB and Kindle. Book excerpt: Microstructure and Texture in Steels and Other Materials comprises a collection of articles pertaining to experimental and theoretical aspects of the evolution of crystallographic texture and microstructure during processing of steels and some other materials. Among the topics covered is the processing-microstructure-texture-property relationship in various kinds of steels, including the latest grade. Special emphasis has been given to introduce recent advances in the characterization of texture and microstructure, as well as modeling. The papers included are written by well-known experts from academia and industrial R and D, which will provide the reader with state-of-the-art, in-depth knowledge of the subject. With these attributes, Microstructure and Texture in Steels and Other Materials is expected to serve the cause of creating awareness of current developments in microstructural science and materials engineering among academic and R and D personnel working in the field.

Download or read book Recommendations for Fatigue Design of Welded Joints and Components written by A. F. Hobbacher and published by Springer. This book was released on 2015-12-23 with total page 153 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides a basis for the design and analysis of welded components that are subjected to fluctuating forces, to avoid failure by fatigue. It is also a valuable resource for those on boards or commissions who are establishing fatigue design codes. For maximum benefit, readers should already have a working knowledge of the basics of fatigue and fracture mechanics. The purpose of designing a structure taking into consideration the limit state for fatigue damage is to ensure that the performance is satisfactory during the design life and that the survival probability is acceptable. The latter is achieved by the use of appropriate partial safety factors. This document has been prepared as the result of an initiative by Commissions XIII and XV of the International Institute of Welding (IIW).

Download or read book Friction Stir Spot Welding of Advanced High Strength Steels written by Jeffrey M. Rodelas and published by . This book was released on 2008 with total page 142 pages. Available in PDF, EPUB and Kindle. Book excerpt: "The application of friction stir spot welding (FSSW) for joining advanced high strength steel (AHSS) offers improvements in automobile fuel economy and crashworthiness. FSSW is a solid-state process and therefore bypasses liquid phases that form during conventional resistance spot welding. This process eliminates detrimental solidification weld defects such as cracking and debonding. A hybrid hi-material FSSW tool comprised of cobalt-cemented tungsten carbide (WC-Co) was bonded to a tungsten-nickel-iron heavy alloy (WHA). A unique sinterbonding process was used to bond the two materials. Sinterbonding WC-Co powder to WHA, using hot pressing to apply pressure, resulted in an ideal consolidated interface. Thermodynamic analyses showed cobalt-rich eta-phase carbides are favored to form at the interface due to a reduction in carbon activity. The mechanical performance of FSSW welds on various AHSS was evaluated. For constant FSSW parameters, martensitic AHSS (M190) did not result in higher lap shear strengths (LSS) compared to dual phase AHSS (DP 590) which has less than half the tensile strength M190. The results suggest that higher strength materials are more resistant to material flow under the tool during welding, which results in smaller bonded regions and LSS. The formation of a strength-reducing soft ferrite layer originating from the sheet faying surfaces was investigated for a martensitic AHSS. A series of welds with varying process times (i.e., varying total energy input) was performed to investigate welding parameter effects on the ferritic layer formation. For the conditions explored, the extent of ferrite formation was dependent on oxygen availability"--Abstract, leaf iv.

Download or read book A Statistical Approach to Quantifying Impact of Multiple Pulse Resistance Spot Welding Schedules on Liquid Metal Embrittlement Cracking written by Erica Wintjes and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Advanced high strength steels (AHSS) are advantageous for automotive applications due to their excellent strength and ductility. However, when coated with zinc for corrosion protection, these steels are susceptible to liquid metal embrittlement (LME) during welding. In this work, a new metric was developed to quantify LME severity and this metric was used to study the influence of multiple pulse weld schedules on LME cracking in resistance spot welds. Several conflicting reports have been released about the effect of LME on mechanical performance of resistance spot welds. In this work, a new method of LME crack quantification called a "Crack Index" was developed to link LME crack distributions in resistance spot welds to weld performance. The crack index is calculated by multiplying the lognormal median crack length by the number of cracks per weld and dividing by the sheet thickness. Because studies have established both crack size and location as vital factors affecting weld strength, both of these factors must be taken into account when characterizing LME severity. Lognormal median crack length is used as the parameter for crack size because the crack lengths measured in LME affected welds were observed to fit a lognormal distribution. Number of cracks is used to account for the probability that a crack may be found in a critical location and sheet thickness is used as a normalization factor. The crack index has a linear relationship with weld strength loss. The crack index analysis method was used to study the influence of multiple pulse welding schedules on LME severity. Pulsing was applied using two different methodologies: pulsing during the welding current to manage heat generation and a pre-pulse before the welding current to remove the zinc coating. All welds made using a double-pulse welding schedule exhibited less severe LME cracking than those made with a single pulse schedule with a similar nugget diameter. A double-pulse schedule with two equal length pulses showed the least severe LME cracking and a schedule consisting of a short pulse followed by a long pulse resulted in the most severe LME. This is due to both a difference in the amount of free zinc available for LME and the different thermal and stress profiles of the pulsing conditions. The majority of pre-pulse welding schedules caused an increase in LME cracking due to the additional heat introduced into the weld. However, a 4 kA pre-pulse (low current), applied for 3 cy (low time) was able to reduce LME cracking in TRIP1100, a LME crack susceptible alloy, by almost 30%. The 4 kA, 3 cy pre-pulse reduced the amount of free zinc for LME, without introducing too much additional heat into the weld.

Download or read book Environment Enhanced Fatigue Crack Growth in High Strength Steels written by R. P. Wei and published by . This book was released on 1973 with total page 57 pages. Available in PDF, EPUB and Kindle. Book excerpt: The current state of understanding of the phenomenology and mechanism(s) for corrosion fatigue of high-strength steels is reviewed. Particular attention is directed towards corrosion fatigue in hydrogen and in water/water vapor environments. Available experimental data indicate that fatigue crack growth in high-strength steels is influenced by loading variables, such as frequency, stress ratio and waveform in regions above and below KIscc. The influences of these variables are directly attributed to interactions with the external chemical environment. Possible synergistic interactions and their relation to chemical reaction kinetics are indicated. Pertinent information on oxygen-metal and water-metal reactions is summarized. Initial results from a coordinated program of study for determining the water-metal reaction kinetics and the kinetics of crack growth on a single high-strength steel are discussed. (Author Modified Abstract).

Download or read book Effect of Lack of Penetration on Fatigue Resistance of High strength Structural Steel Welds written by Y. Tobe and published by . This book was released on 1977 with total page 38 pages. Available in PDF, EPUB and Kindle. Book excerpt: Zero-to-tension fatigue tests were carried out on double-V butt welds of ASTM A514 steel plate, 20 mm in thickness, which contained full-length lack of penetration (LOP) defects. The fatigue crack initiation and propagation portions of the specimens' fatigue lives were experimentally separated. Compression-to-tension fatigue tests were carried out on prime base plate, as-welded sound joints, and reinforcement-removed welds to experimentally determine the fatigue strength reduction factor (Kf) of the LOP defects. LOP defects as small as 0.5 mm wide had a profound effect on fatigue life. The fatigue crack initiation life was found to be short-only 10 percent of the total life-and could be predicted using fatigue crack initiation concepts. The use of KF(max), the maximum possible fatigue strength reduction factor, was found to be appropriate. In a separate substudy, the fatigue resistance of ASTM A514 butt-welded joints containing clustered porosity was determined. (Author).

Download or read book Development of Appropriate Spot Welding Practice for Advanced High Strength Steels TRP 0114 written by Jerry Gould and published by . This book was released on 2004 with total page 46 pages. Available in PDF, EPUB and Kindle. Book excerpt: This program evaluated the effects of common manufacturing variables on spike-tempering effectiveness. The investigation used design-of-experiment (DOE) techniques, and examined both dual-phase and martensitic grades of high-strength steels (HSS). The specific grades chosen for this project were: Dual-phase (DP) 600, galvannealed (GA), 1.55 mm (DP) 600; Dual-phase (DP) 980 (uncoated), 1.55 mm (DP) 980; and Martensitic (M) 1300, 1.55 mm (M) 1300. Common manufacturing conditions of interest included tempering practice (quench and temper time), button size, simulated part fitup (sheet angular misalignment and fitup), and electrode wear (increased electrode face diameter). All of these conditions were evaluated against mechanical performance (static and dynamic tensile shear). Weld hardness data was also used to examine correlations between mechanical performance and the degree of tempering. Mechanical performance data was used to develop empirical models. The models were used to examine the robustness of weld strength and toughness to the selected processing conditions. This was done using standard EWI techniques. Graphical representations of robustness were then coupled with metallographic data to relate mechanical properties to the effectiveness of spike tempering. Mechanical properties for all three materials were relatively robust to variation in tempering. Major deviations in mechanical properties were caused by degradation of the weld itself. This was supported by a lack of correlation between hardness data and mechanical results. Small button sizes and large electrode face diameters (worn electrodes) produced large reductions in both static and dynamic strength levels when compared to standard production setups. Dynamic strength was further degraded by edge-located welds.