112 research outputs found

    Hardness-based plasticity and fracture model for quench-hardenable boron steel (22MnB5)

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    A comprehensive strain hardening and fracture characterization of different grades of boron steel blanks has been performed, providing the foundation for the implementation into the modular material model (MMM) framework developed by Volkswagen Group Research for an explicit crash code. Due to the introduction of hardness-based interpolation rules for the characterized main grades, the hardening and fracture behavior is solely described by the underlying Vickers hardness. In other words, knowledge of the hardness distribution within a hot-formed component is enough to set up the newly developed computational model. The hardness distribution can be easily introduced via an experimentally measured hardness curve or via hardness mapping from a corresponding hot-forming simulation. For industrial application using rather coarse and computationally inexpensive shell element meshes, the user material model has been extended by a necking/post-necking model with reduced mesh-dependency as an additional failure mode. The present paper mainly addresses the necking/post-necking model

    Identification of plasticity model parameters of the heat-affected zone in resistance spot welded martensitic boron steel

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    A material model is developed that predicts the plastic behavior of fully hardened 22MnB5 base material and the heat-affected zone (HAZ) material found around its corresponding resistance spot welds (RSWs). Main focus will be on an accurate representation of strain fields up to high strains, which is required for subsequent calibration of the fracture behavior of both base material and HAZ. The plastic be-havior of the base material is calibrated using standard tensile tests and notched tensile tests and an inverse FEM optimization algorithm. The plastic behavior of the HAZ material is characterized using a specially designed tensile specimen with a HAZ in the gage section. The exact location of the HAZ relative to the center of the RSW is determined using microhardness measurements, which are also used for mapping of the material properties into an FE-model of the specimen. With the parameters of the base material known, and by assuming a linear relation between the hardness and the plasticity model parameters of base material and HAZ, the unknown HAZ parameters are determined using inverse FEM optimization. A coupon specimen with HAZ is used to validate the model at hand

    Characterization of Loading Responses and Failure Loci of a Boron Steel Spot Weld

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    Boron steel, classed as an ultra high-strength steel (UHSS), has been utilized in anti-intrusion systems in automobiles, providing high strength and weight-saving potential through gage reduction. UHSS spot welds exhibit unique hardness distributions, with a hard nugget and outlying base material, but with a soft heat-affected zone in-between these regions. This soft zone reduces the strength of the weld and makes it susceptible to failure. Due to the interaction of various weld zones that occurs during loading, there is a need to characterize the loading response of the weld for accurate failure predictions. The loading response of certain weld zones, as well as failure loci, was obtained through physical simulation of the welding process. The results showed a significant difference in mechanical behavior through the weld length. An important result is that instrumented indentation was shown to be a valid, quantitative method for verifying the accuracy with which weld microstructure has been recreated with regard to the target weld microstructure

    Search for neutral resonances decaying into a Z boson and a pair of b jets or τ leptons

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    A search is performed for a new resonance decaying into a lighter resonance and a Z boson. Two channels are studied, targeting the decay of the lighter resonance into either a pair of oppositely charged τ leptons or a bb‾ pair. The Z boson is identified via its decays to electrons or muons. The search exploits data collected by the CMS experiment at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 19.8 fb −1 . No significant deviations are observed from the standard model expectation and limits are set on production cross sections and parameters of two-Higgs-doublet models

    Search for a low-mass pseudoscalar Higgs boson produced in association with a bb⁻ pair in pp collisions at √s=8 TeV

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    A search is reported for a light pseudoscalar Higgs boson decaying to a pair of tau leptons, produced in association with a b (b) over bar pair, in the context of two-Higgs-doublet models. The results are based on pp collision data at a centre-of-mass energy of 8 TeV collected by the CMS experiment at the LHC and corresponding to an integrated luminosity of 19.7 fb(-1). Pseudoscalar boson masses between 25 and 80 GeV are probed. No evidence for a pseudoscalar boson is found and upper limits are set on the product of cross section and branching fraction to tau pairs between 7 and 39 pb at the 95% confidence level. This excludes pseudoscalar A bosons with masses between 25 and 80 GeV, with SM-like Higgs boson negative couplings to down-type fermions, produced in association with bb pairs, in Type II, two-Higgs-doublet models. (C) 2016 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommonnorg/licensesiby/4.01)

    Phenomenological MSSM interpretation of CMS searches in pp collisions at √s=7 and 8 TeV

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    Searches for new physics by the CMS collaboration are interpreted in the framework of the phenomenological minimal supersymmetric standard model (pMSSM). The data samples used in this study were collected at root s = 7 and 8 TeV and have integrated luminosities of 5.0 fb(-1) and 19.5 fb(-1), respectively. A global Bayesian analysis is performed, incorporating results from a broad range of CMS supersymmetry searches, as well as constraints from other experiments. Because the pMSSM incorporates several well-motivated assumptions that reduce the 120 parameters of the MSSM to just 19 parameters defined at the electroweak scale, it is possible to assess the results of the study in a relatively straightforward way. Approximately half of the model points in a potentially accessible subspace of the pMSSM are excluded, including all pMSSM model points with a gluino mass below 500 GeV, as well as models with a squark mass less than 300 GeV. Models with chargino and neutralino masses below 200 GeV are disfavored, but no mass range of model points can be ruled out based on the analyses considered. The nonexcluded regions in the pMSSM parameter space are characterized in terms of physical processes and key observables, and implications for future searches are discussed

    Search for massive WH resonances decaying into the l nu b(b)over-bar final state at root s=8 TeV

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    Peer reviewe

    Search for vectorlike charge 2/3 T quarks in proton-proton collisions at root(s)=8 TeV

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    Forward-backward asymmetry of Drell-Yan lepton pairs in pp collisions at root s=8 TeV

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    Search for single production of scalar leptoquarks in proton-proton collisions at root s=8 TeV

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    Correction DOI:10.1103/PhysRevD.95.039906Peer reviewe
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