The Experts below are selected from a list of 5880 Experts worldwide ranked by ideXlab platform

Tom Eller - One of the best experts on this subject based on the ideXlab platform.

  • plasticity and fracture modeling of the heat affected zone in resistance spot welded tailor hardened Boron Steel
    Journal of Materials Processing Technology, 2016
    Co-Authors: Tom Eller, Lars Greve, M T Andres, M Medricky, H J M Geijselaers, Vincent T Meinders, Van Den A H Boogaard
    Abstract:

    tFive hardness grades of 22MnB5 are considered, covering the full strength-range from 600 MPa in theferritic/pearlitic range to 1500 MPa in the fully hardened, martensitic state. These five grades form thebasis for a hardness-based material model for the heat-affected zone found around resistance spot weldsin tailor hardened Boron Steel. Microhardness measurements of resistance spot welds in all five gradesare used to determine the location and shape of the heat-affected zone and for mapping of the hardnessdistributions into FE-models of the specimens used for model calibration. For calibration of the strainhardening of the heat-affected zone, a specially designed asymmetric uni-axial tensile specimen is usedthat features a well-defined strain field up to fracture initiation. Both the measured force–displacementcurves and the strain fields are used as input for an inverse FEM optimization algorithm that identifiessuitable strain hardening model parameters by minimizing the differences between experimental andsimulated results. A strain-based fracture model is calibrated using a hybrid experimental/numericalapproach, featuring two additional specimens in which fracture initiates in the HAZ under differentstress states. Strain hardening and fracture strains are assumed to be linearly related to the as-weldedmaterial hardness. The calibration and modeling approach are validated by comparing measured andpredicted force–displacement curves and strain fields of welded coupon tensile tests.

  • the softened heat affected zone in resistance spot welded tailor hardened Boron Steel a material model for crash simulation
    International Conference on Impact Loading of Structures and Materials (ICILSM): International Conference on Impact Loading of Structures and Material, 2016
    Co-Authors: Tom Eller, Lars Greve, M T Andres, M Medricky, H J M Geijselaers, Vincent T Meinders, Antonius H Van Den Boogaard
    Abstract:

    A hardness-based model for tailor hardened Boron Steel is presented that takes into account the softened heat-affected zone of resistance spot welds. The computational model is designed for crashworthiness simulation of fully and partially hardened components obtained by tailored tooling. Five different hardness grades of 22MnB5 are used for model calibration. The proposed model is validated with a specially designed tapered tensile test specimen with hardness transition zone and resistance spot weld in the gauge section.

  • plasticity and fracture modeling of quench hardenable Boron Steel with tailored properties
    Journal of Materials Processing Technology, 2014
    Co-Authors: Tom Eller, Lars Greve, M T Andres, M Medricky, Vincent T Meinders, A Hatscher, A H Van Den Boogaard
    Abstract:

    In this article, a constitutive model for quench-hardenable Boron Steel is presented. Three sets of Boron Steel blanks are heat treated such that their as-treated microstructures are close to fully martensitic, bainitic and ferritic/pearlitic, respectively. Hardness measurements show that the resulting blanks cover the full scope of possible hardness values, from 165 HV in the ferritic/pearlitic range to 477 HV in the fully hardened state. These three main grades provide the input data for a constitutive model consisting of an extended Swift hardening law and a stress triaxiality and Lode angle dependent fracture criterion. The hardening behavior of each grade is determined using standard tensile tests at quasi-static strain rates. The strain-based fracture criterion is calibrated using four different flat fracture samples. The behavior of intermediate hardness grades is approximated by piecewise linear combination of the three calibrated constitutive models. A newly developed tapered tensile test specimen featuring a hardness transition zone in the gauge section is used to verify the model at hand. A four point bending test of a top hat section of intermediate hardness is used to verify the model for complex loading conditions.

Andrea Ghiotti - One of the best experts on this subject based on the ideXlab platform.

  • hot stamping of Boron Steel sheets with tailored properties a review
    Journal of Materials Processing Technology, 2016
    Co-Authors: Marion Merklein, Stefania Bruschi, Michael Wieland, Michael Lechner, Andrea Ghiotti
    Abstract:

    Abstract The paper gives a review of the main research activities recently carried out in the framework of hot stamping of Boron Steel sheets with tailored properties. The focus is on the process variants developed to locally adjust the mechanical properties of the hot stamped component as well as on the testing and modeling techniques needed to calibrate the numerical models of the tailored tempering processes and to evaluate the post-forming properties of the stamped products.

  • comparison of tribological and wear performances of alsi and zn coatings in hot stamping of Boron Steel sheets
    Wear, 2015
    Co-Authors: Andrea Ghiotti, Stefania Bruschi, Francesco Medea
    Abstract:

    Abstract Since direct hot stamping has become the most relevant technology to manufacture 22MnB5 structural parts for automotive industry, the knowledge of the tribological conditions and the comprehension of the wear mechanisms are crucial for the process competitiveness. AlSi and Zn coatings, which are currently the most used to coat the Steel sheets in order to avoid scale formation in the furnace, are supposed to act as lubricants during the forming stage. However, the thermal and mechanical conditions at the blank-dies interface may change significantly within the forming stage, depending on the geometrical features of the dies and the process parameters, so making critical the integrity of the coatings itself. The paper presents the results of experimental investigations on the tribological performances of AlSi and Zn coatings applied to 22MnB5, reproducing the different thermal conditions at the blank-die interfaces. Frictional and wear tests, reproducing the thermo-mechanical conditions typical of hot stamping, were carried out in the temperature range from 800 °C down to 600 °C. The results show lower friction coefficients for the Zn coating. For both the coatings, the dies wear appears as a combination of adhesion and abrasion, with the latter more relevant at the lower temperatures. Both the coatings show worse performances when the test temperatures are decreased.

  • tribological performances of zn based coating in direct hot stamping
    Tribology International, 2014
    Co-Authors: Andrea Ghiotti, Francesco Sgarabotto, Stefania Bruschi, Paolo Francesco Bariani
    Abstract:

    Abstract In hot stamping of High Strength Steels, the severe tribological conditions make the metal sheet coating one of the most critical choices for the technical and economical success of the process. This paper presents the approach and the results in evaluating a Zinc-based coating applied to Boron Steel sheets in hot stamping operations. Thermal and physical-simulation experiments were carried out to evaluate the chemical interactions between the coating and the metal sheet and the tribological performances during the process. The coating proved to overcome most of the drawbacks of the currently utilized Al–Si coating.

  • a novel approach to wear testing in hot stamping of high strength Boron Steel sheets
    Wear, 2013
    Co-Authors: Andrea Ghiotti, Francesco Sgarabotto, Stefania Bruschi
    Abstract:

    Abstract Hot stamping of high strength Steel sheets was developed in the automotive industry for the production of components characterized by a high strength-to-weight ratio and an increased resistance to impact. In order to avoid scaling and decarburization, the Steel blanks are usually coated with an Al–Si coating that has proved a relevant influence also on their tribological behaviour during the forming stages. However, the knowledge of the influence that this coating may have on the dies wear mechanisms is still inadequate. The paper proposes a novel approach to wear testing, based on a pin-on-disk testing configuration, capable to reproduce in a laboratory environment the conditions arising at the interface between the dies and the blank, by reproducing the sliding velocities at the interface and the cyclic thermal and mechanical stresses on the die material. Investigations were carried out on a hot working tool Steel sliding against high strength Steel blanks coated with the Al–Si coating under dry reciprocating sliding conditions. Scanning electron microscopy and 3D profilometer analysis were utilized to evaluate the wear mechanisms. The presented results show that the proposed procedure can properly simulate the thermal and mechanical cycles to which the forming dies are subjected during the hot stamping process, allowing to control and vary a number of parameters characterizing the industrial process. The presence of both adhesive and abrasive wear mechanisms is highlighted and a possible explanation of their appearance is given.

Wei Zhang - One of the best experts on this subject based on the ideXlab platform.

  • microstructure and strength of ultrasonic plus resistance spot welded aluminum alloy to coated press hardened Boron Steel
    Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2020
    Co-Authors: Luke Walker, M Kimchi, Wei Zhang
    Abstract:

    Press-hardened Boron Steels with ultrahigh strength (above 1500 MPa) are widely used in crash-sensitive safety components in automobiles. Joining such Steels to aluminum alloys is challenging due to various factors including the Steel’s tenacious Al-Si coating. A novel application of ultrasonic plus resistance spot welding was developed for such dissimilar metal joining. The nugget formation and the interface microstructure especially intermetallics formed were correlated to the joint strength, ductility and failure behavior.

  • subcritical heat affected zone softening in hot stamped Boron Steel during resistance spot welding
    Materials & Design, 2018
    Co-Authors: Andrea Peer, Tim Abke, M Kimchi, Wei Zhang
    Abstract:

    Abstract Highly non-uniform temperature gradients experienced by workpieces during resistance spot welding (RSW) can lead to the formation of a subcritical heat affected zone (SCHAZ), a region prone to “premature” failure for ultra-high strength Steels. Accurate prediction of spot weld properties such as surface electrode indentation and local hardness is essential for computer-aided engineering (CAE) based design of light-weight and impact-resistant structures. In this study, a 3D fully coupled electro-thermo-mechanical model incorporating an improved electrical contact resistance formula from the literature is developed for resistance spot welding of aluminium‑silicon coated hot-stamped Boron Steel. The temperature profiles, contact pressure distribution, nugget formation, and electrode indentation during RSW are numerically investigated. Tempering kinetics of base metal martensite is experimentally measured by isothermal tempering tests and used to extract kinetics parameters for a Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation. The non-isothermal JMAK equation coupled with the process model is shown to accurately predict local SCHAZ softening.

Vincent T Meinders - One of the best experts on this subject based on the ideXlab platform.

  • plasticity and fracture modeling of the heat affected zone in resistance spot welded tailor hardened Boron Steel
    Journal of Materials Processing Technology, 2016
    Co-Authors: Tom Eller, Lars Greve, M T Andres, M Medricky, H J M Geijselaers, Vincent T Meinders, Van Den A H Boogaard
    Abstract:

    tFive hardness grades of 22MnB5 are considered, covering the full strength-range from 600 MPa in theferritic/pearlitic range to 1500 MPa in the fully hardened, martensitic state. These five grades form thebasis for a hardness-based material model for the heat-affected zone found around resistance spot weldsin tailor hardened Boron Steel. Microhardness measurements of resistance spot welds in all five gradesare used to determine the location and shape of the heat-affected zone and for mapping of the hardnessdistributions into FE-models of the specimens used for model calibration. For calibration of the strainhardening of the heat-affected zone, a specially designed asymmetric uni-axial tensile specimen is usedthat features a well-defined strain field up to fracture initiation. Both the measured force–displacementcurves and the strain fields are used as input for an inverse FEM optimization algorithm that identifiessuitable strain hardening model parameters by minimizing the differences between experimental andsimulated results. A strain-based fracture model is calibrated using a hybrid experimental/numericalapproach, featuring two additional specimens in which fracture initiates in the HAZ under differentstress states. Strain hardening and fracture strains are assumed to be linearly related to the as-weldedmaterial hardness. The calibration and modeling approach are validated by comparing measured andpredicted force–displacement curves and strain fields of welded coupon tensile tests.

  • the softened heat affected zone in resistance spot welded tailor hardened Boron Steel a material model for crash simulation
    International Conference on Impact Loading of Structures and Materials (ICILSM): International Conference on Impact Loading of Structures and Material, 2016
    Co-Authors: Tom Eller, Lars Greve, M T Andres, M Medricky, H J M Geijselaers, Vincent T Meinders, Antonius H Van Den Boogaard
    Abstract:

    A hardness-based model for tailor hardened Boron Steel is presented that takes into account the softened heat-affected zone of resistance spot welds. The computational model is designed for crashworthiness simulation of fully and partially hardened components obtained by tailored tooling. Five different hardness grades of 22MnB5 are used for model calibration. The proposed model is validated with a specially designed tapered tensile test specimen with hardness transition zone and resistance spot weld in the gauge section.

  • plasticity and fracture modeling of quench hardenable Boron Steel with tailored properties
    Journal of Materials Processing Technology, 2014
    Co-Authors: Tom Eller, Lars Greve, M T Andres, M Medricky, Vincent T Meinders, A Hatscher, A H Van Den Boogaard
    Abstract:

    In this article, a constitutive model for quench-hardenable Boron Steel is presented. Three sets of Boron Steel blanks are heat treated such that their as-treated microstructures are close to fully martensitic, bainitic and ferritic/pearlitic, respectively. Hardness measurements show that the resulting blanks cover the full scope of possible hardness values, from 165 HV in the ferritic/pearlitic range to 477 HV in the fully hardened state. These three main grades provide the input data for a constitutive model consisting of an extended Swift hardening law and a stress triaxiality and Lode angle dependent fracture criterion. The hardening behavior of each grade is determined using standard tensile tests at quasi-static strain rates. The strain-based fracture criterion is calibrated using four different flat fracture samples. The behavior of intermediate hardness grades is approximated by piecewise linear combination of the three calibrated constitutive models. A newly developed tapered tensile test specimen featuring a hardness transition zone in the gauge section is used to verify the model at hand. A four point bending test of a top hat section of intermediate hardness is used to verify the model for complex loading conditions.

Lars Greve - One of the best experts on this subject based on the ideXlab platform.

  • plasticity and fracture modeling of the heat affected zone in resistance spot welded tailor hardened Boron Steel
    Journal of Materials Processing Technology, 2016
    Co-Authors: Tom Eller, Lars Greve, M T Andres, M Medricky, H J M Geijselaers, Vincent T Meinders, Van Den A H Boogaard
    Abstract:

    tFive hardness grades of 22MnB5 are considered, covering the full strength-range from 600 MPa in theferritic/pearlitic range to 1500 MPa in the fully hardened, martensitic state. These five grades form thebasis for a hardness-based material model for the heat-affected zone found around resistance spot weldsin tailor hardened Boron Steel. Microhardness measurements of resistance spot welds in all five gradesare used to determine the location and shape of the heat-affected zone and for mapping of the hardnessdistributions into FE-models of the specimens used for model calibration. For calibration of the strainhardening of the heat-affected zone, a specially designed asymmetric uni-axial tensile specimen is usedthat features a well-defined strain field up to fracture initiation. Both the measured force–displacementcurves and the strain fields are used as input for an inverse FEM optimization algorithm that identifiessuitable strain hardening model parameters by minimizing the differences between experimental andsimulated results. A strain-based fracture model is calibrated using a hybrid experimental/numericalapproach, featuring two additional specimens in which fracture initiates in the HAZ under differentstress states. Strain hardening and fracture strains are assumed to be linearly related to the as-weldedmaterial hardness. The calibration and modeling approach are validated by comparing measured andpredicted force–displacement curves and strain fields of welded coupon tensile tests.

  • the softened heat affected zone in resistance spot welded tailor hardened Boron Steel a material model for crash simulation
    International Conference on Impact Loading of Structures and Materials (ICILSM): International Conference on Impact Loading of Structures and Material, 2016
    Co-Authors: Tom Eller, Lars Greve, M T Andres, M Medricky, H J M Geijselaers, Vincent T Meinders, Antonius H Van Den Boogaard
    Abstract:

    A hardness-based model for tailor hardened Boron Steel is presented that takes into account the softened heat-affected zone of resistance spot welds. The computational model is designed for crashworthiness simulation of fully and partially hardened components obtained by tailored tooling. Five different hardness grades of 22MnB5 are used for model calibration. The proposed model is validated with a specially designed tapered tensile test specimen with hardness transition zone and resistance spot weld in the gauge section.

  • plasticity and fracture modeling of quench hardenable Boron Steel with tailored properties
    Journal of Materials Processing Technology, 2014
    Co-Authors: Tom Eller, Lars Greve, M T Andres, M Medricky, Vincent T Meinders, A Hatscher, A H Van Den Boogaard
    Abstract:

    In this article, a constitutive model for quench-hardenable Boron Steel is presented. Three sets of Boron Steel blanks are heat treated such that their as-treated microstructures are close to fully martensitic, bainitic and ferritic/pearlitic, respectively. Hardness measurements show that the resulting blanks cover the full scope of possible hardness values, from 165 HV in the ferritic/pearlitic range to 477 HV in the fully hardened state. These three main grades provide the input data for a constitutive model consisting of an extended Swift hardening law and a stress triaxiality and Lode angle dependent fracture criterion. The hardening behavior of each grade is determined using standard tensile tests at quasi-static strain rates. The strain-based fracture criterion is calibrated using four different flat fracture samples. The behavior of intermediate hardness grades is approximated by piecewise linear combination of the three calibrated constitutive models. A newly developed tapered tensile test specimen featuring a hardness transition zone in the gauge section is used to verify the model at hand. A four point bending test of a top hat section of intermediate hardness is used to verify the model for complex loading conditions.