Download or read book Development of Mechanism based Models for Resistance Spot Weld Failure Simulation of Multi material Advanced High Strength Steel Sheets written by Daniel Dorribo Dorribo and published by . This book was released on 2018 with total page 160 pages. Available in PDF, EPUB and Kindle. Book excerpt: The automotive industry is constantly involved in the development of new projects aimed at reducing weight, fuel consumptions and costs while improving passengers¿ safety. In order to achieve these increasing demands, Advanced High Strength Steels (AHSS) have been introduced in recent years reducing vehicle structure weights and improving the crashworthiness. With the increase in the bearing capacity of crash-relevant structural components, the sheet metal joining techniques such as adhesive bonding and resistance spot welding (RSW) become critical. In order to develop the vehicle structure in these new projects, full-vehicle crash finite element simulations are usually performed. Simplified beam-like models are currently used in these simulations (with thousands of spot welds) to represent RSW joints response. The maximum bearing force of these models are fitted using large experimental campaigns, considering all the main factors that have the highest influence on the fracture response of a welded joint. The objective of this thesis is twofold: (1) to develop a model that is able to partially replace the extensive experimental campaign in providing parameters for the crash simulation simplified spot weld models, and (2) to gain understanding of spot weld joints failure response in order to improve the current simplified models. To achieve these objectives, a detailed spot weld model for the prediction of spot weld failure in joints in AHSS sheets is presented. The presented model includes a definition of the local material properties as well as the geometry features of a spot weld. In addition, an industrially suited fracture criterion, i.e. robust and without a long-term calibration, is used for the prediction of maximum force. An energetic fracture criterion based on the use of elastic-plastic fracture-mechanics is identified as the better suited for the prediction of spot weld failure and joint bearing capacity. The J-integral is evaluated in the weld notch and this value is compared with a material parameter, the fracture toughness, in order to obtain the joint maximum force. The presented detailed FE spot weld model is validated to joints of two different steel grades of the AHSS family usually present in the current vehicle structure, a hot formed martensitic boron-alloyed steel (22MnB5) and a cold formed dual phase steel (DP 980). The validation is performed comparing the results obtained with the finite element model and the experimental results extracted from an extensive loading test experimental campaign where the main factors that have an influence in the spot weld fracture response are considered. The obtained simulated critical forces of the loading tests present good agreement with the experimental ones in all tested configurations. Finally, based on the presented finite element spot weld model, some recommendations are exposed for extending the model for new combinations and loading conditions. The proposed procedure can be used to reduce the long-term characterization campaigns used to calibrate the joints of a new AHSS grade, where fracture is triggered by stress concentration ahead of a notch. Furthermore, some recommendations for the future structure design are given taking into account the information obtained with the present model.

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 Investigation of Resistance Spot Weld Failure in Tailored Hot Stamped Assemblies written by Cameron O'Keeffe and published by . This book was released on 2018 with total page 164 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis presents the results from the mechanical characterization of resistance spot welds within hot stamped USIBOR® 1500-AS steel sheet (1.2 and 1.6 mm thickness) with tailored properties. Three parent metal conditions, ranging from a fully martensitic (495 HV) to a mixed ferritic-bainitic microstructure (211 HV), were obtained using in-die heating (IDH) to control the cooling (quench) rate during the hot stamping process. Flat sheets and hat channel geometries were produced through die quenching in which the die was maintained at 25, 400, and 700°C with strengths of 1,548, 817, and 671 MPa, respectively. The as-quenched sheets were resistance spot welded and mechanically tested in lap shear, cross tension, V-bend, and JIS tensile coupon geometries to characterize the mechanical response of single welds under various loading orientations. Hardness testing was conducted on the welds to investigate the hardness (strength) distribution in the welded region, heat affected zone (HAZ) and parent metal. The drop in hardness within the HAZ increased as the parent metal strength increased, such that the hardness of the HAZ was similar for all three spot welded parent metals (211-318 HV). In the mechanical testing, strain localized in the HAZ (or nugget) with the result that the strength of the welds was relatively constant for all die quench conditions. For the range of material conditions considered, the lowest weld strength 4.0-4.5 kN was measured in the cross-tension tests compared to 12.1-15.0 kN for the lap shear tests (data for 1.2 mm sheet). A new mechanical test, termed the “Caiman”, was developed to study groups of welds under both static and dynamic Mode I structural loading. Channel sections comprising of fully quenched material as well as hot stamped components with tailored, lower strength flanges were joined via spot welding. The experiments subjected the welded regions to Mode I tensile loading to investigate how failure propagated along the spot weld line. It was found that the energy absorption within the welded connections was higher for the lower strength (tailored) parent metal conditions, largely due to activation of plastic deformation within the parent metal as opposed to the fully martensitic condition for which deformation was confined to the weld nugget or HAZ. High speed thermal imaging was shown to be an effective method to detect failure of individual welds and track failure propagation within the welded assembly due to local adiabatic heating associated with weld fracture or pullout. Temperature increases of 7 °C were typical of quasi-static loading whereas increases of 80 °C were observed under dynamic loading. It was determined that initiation of the first weld failure was delayed slightly under dynamic loading (relative to quasi-static); however, failure propagation after initiation was more rapid for dynamic loading for a given load point displacement. Numerical simulations of the lap shear and cross tension single weld experiments were used to calibrate weld failure models within the commercial finite element software LS DYNA, with relatively good correlation to the experimental data. The calibration exercise revealed the importance of simulation of the post failure response, in particular the use of the “fade energy” numerical parameter, to more accurately capture the energy released during the weld fracture event. The weld failure models calibrated from the single weld tests were applied to simulate the static and dynamic Caiman experiments without additional “tuning”. For the quasi-static Caiman simulations, the predicted load-displacement response and failure propagation were relatively accurate, with higher errors for the fully martensitic case since the HAZ was not modelled. The dynamic simulations aligned relatively well with the experimental results.

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 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 A Unified Approach to Assessing the Mechanical Performance of Resistance Spot Welds written by Mingxing Zhou and published by . This book was released on 2001 with total page 280 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Performance Testing and Modeling of Ultra high Strength Steel and Complex Stack up Resistance Spot Welds written by Andrea J. Peer and published by . This book was released on 2017 with total page 155 pages. Available in PDF, EPUB and Kindle. Book excerpt: The knowledge generated in this study can help improve the accuracy of predicting spot weld fracture of ultra-high strength steels in the automotive industry. Particularly, the fine-resolution, coupon-scale model developed in this research will be useful for implementation into coarse-resolution, full-scale models for crash simulation and optimization of vehicle components.

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 Modeling Steel Deformation in the Semi Solid State written by Marcin Hojny and published by Springer. This book was released on 2017-09-07 with total page 304 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book offers a unique approach to integrated high-temperature process modelling, intended to serve as a design aid for new metal processing technologies. The second edition has been substantially expanded to include new content such as: a new algorithm and test results of 3D stereoscopic visualization; new programming procedures for modelling; the validation of computer simulation using experimental results; a multiscale model of grain growth; a conceptual methodology developing “high-temperature” CCT (continuous cooling transformation) diagrams, and many more examples validating the numerical simulations. The models presented are applied in comprehensive tests in order to solve problems related to the high-temperature deformation of steel. The testing methods include both physical tests using specialist laboratory instruments, and advanced mathematical modelling: the Finite Element method (FE), Smoothed Particle Hydrodynamics method (SPH) and Mo nte Carlo method (MC).This approach, which integrates the fields of physical and computer-based simulations, forms the basis for the described concept of integrated high-temperature process modelling, presented in detail in this book.

Download or read book On Material Modelling of High Strength Steel Sheets written by Rikard Larsson and published by . This book was released on 2012 with total page 58 pages. Available in PDF, EPUB and Kindle. Book excerpt: The work done in this thesis aims at developing and improving material models for use in industrial applications.??The mechanical behaviour of three advanced high strength steel grades, Docol 600DP, Docol 1200M and HyTens 1000, has been experimentally investigated under various types of deformation, and material models of their behaviour have been developed. The origins of all these material models are experimental findings from physical tests on the materials.??Sheet metal forming is an important industrial process and is used to produce a wide range of products. The continuously increasing demand on the weight to performance ratio of many products promotes the use of advanced high strength steel. In order to take full advantage of such steel, most product development is done by means of computer aided engineering, CAE. In advanced product development, the use of simulation based design, SBD, is continuously increasing. With SBD, the functionality of a product, as well as its manufacturing process, can be analysed and optimised with a minimum of physical prototype testing. Accurate numerical tools are absolutely necessary with this methodology, and the model of the material behaviour is one important aspect of such tools.??This thesis consists of an introduction followed by five appended papers. In the first paper, the dual phase Docol 600DP steel and the martensitic Docol 1200M steel were subjected to deformations, both under linear and non-linear strain paths. Plastic anisotropy and hardening were evaluated and modelled using both virgin materials, i.e. as received, and materials which were pre-strained in various material directions.??In the second paper, the austenitic stainless steel HyTens 1000 was subjected to deformations under various proportional strain paths and strain rates. It was experimentally shown that this material is sensitive both to dynamic and static strain ageing. A constitutive model accounting for these effects was developed, calibrated, implemented in a Finite Element software and, finally, validated on physical test data.??The third paper concerns the material dispersions in batches of Docol 600DP. A material model was calibrated to a number of material batches of the same steel grade. The paper provides a statistical analysis of the resulting material parameters.??The fourth paper deals with a simple modelling of distortional hardening. This type of hardening is able to represent the variation of plastic anisotropy during deformation. This is not the case with a regular isotropic hardening, where the anisotropy is fixed during deformation.??The strain rate effect is an important phenomenon, which often needs to be considered in a material model. In the fifth paper, the strain rate effects in Docol 600DP are investigated and modelled. Furthermore, the strain rate effect on strain localisation is discussed.

Download or read book Metals Abstracts written by and published by . This book was released on 1996 with total page 1628 pages. Available in PDF, EPUB and Kindle. Book excerpt:

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 Technical Literature Abstracts written by Society of Automotive Engineers and published by . This book was released on 2000 with total page 400 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Assessment of Resistance Spot Welds in Low Carbon and High Strength Steel Sheet written by R. M. Rivett and published by . This book was released on 1982 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Fea of Resistance Spot Welding written by Amol Rasane and published by LAP Lambert Academic Publishing. This book was released on 2011-07 with total page 76 pages. Available in PDF, EPUB and Kindle. Book excerpt: Resistance spot welding is the most commonly used method for joining steel sheets. It is a complex process in which coupled interactions exist between electrical, thermal, mechanical, metallurgical phenomena and even surface behaviors. Because of this complexity, it is very difficult to obtain insightful information of welding process through the experiments alone. Physical weld simulators that simulate the weld by heating and cooling the material have been used in the past. On the other hand, numerical modeling and simulation provides a powerful tool in studying these interactions. These types of simulations are nowadays used as a part of the product development process. By replacing physical testing with computer simulations, a lot of time and money can be saved and more design solutions can be numerically tested leading to more reliable products. This work provides a step by step method for simulating the spot welding process by using finite element method. It is useful for the professionals using spot welding process extensively and can help them improve their production process as well as product development capability.

Download or read book Stiffness Energy Absorption Fatigue of High strength Steel Structures in Relation to Applied Joining and Forming Technologies and Mechanical Properties written by and published by . This book was released on 2002 with total page 220 pages. Available in PDF, EPUB and Kindle. Book excerpt: