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  • 1.
    Kang, Yuchi
    et al.
    Kunming Univ Sci & Technol, CHN.
    Liu, Meihong
    Kunming Univ Sci & Technol, CHN.
    Hu, Xiangping
    Norwegian Univ Sci & Technol, NOR.
    Kao-Walter, Sharon
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Zhang, Baodi
    Kunming Univ Sci & Technol, CHN.
    Theoretical and numerical investigation into brush seal hysteresis without pressure differential2019In: Advanced Composites Letters, ISSN 0963-6935, Vol. 28, article id UNSP 0963693519885386Article in journal (Refereed)
    Abstract [en]

    Brush seal is a novel type contact seal, and it is well-known due to its excellent performance. However, there are many intrinsic drawbacks, such as hysteresis, which need to be solved. This article focused on modeling hysteresis in both numerical way and analytic way without pressure differential. The numerical simulation was solved by the finite element method. General contact method was used to model the inter-bristle contact, bristle-rotor contact, and bristle-backplate contact. Bristle deformation caused by both vertical and axial tip force was used to validate the numerical model together with reaction force. An analytic model in respect of the strain energy was created. The influence of structure parameters on the hysteresis ratio, with the emphasis on the derivation of hysteresis ratio formula for brush seals, was also presented. Both numerical model and analytic model presented that cant angle is the most influential factor. The aim of the article is to provide a useful theoretical and numerical method to analyze and predict the hysteresis. This work contributes the basis for future hysteresis investigation with pressure differential.

  • 2.
    PENG, WU
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Levin, Sebastian
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Chatter Vibration Damping in Parting Tools2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 3.
    Pilthammar, Johan
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Banabic, Dorel
    Tech Univ Cluj Napoca, ROU.
    Sigvant, Mats
    Volvo Cars, SWE.
    BBC05 with non-integer exponent and ambiguities in Nakajima yield surface calibration2020In: International Journal of Material Forming, ISSN 1960-6206, E-ISSN 1960-6214Article in journal (Refereed)
    Abstract [en]

    Reliable sheet metal forming simulations depend on accurate descriptions of real process conditions. These conditions include material behavior, lubrication systems, tool deformations, press dynamics, and more. Research on material models is the most mature area for describing these conditions in a reliable way. Several advanced and flexible models exists. This study focuses on two versions of yield criteria for sheet materials that are assumed to follow the plane stress assumption: the BBC05 model with integer exponent and the BBC05 model with non-integer exponent. The literature has previously described the BBC05 model with integer exponent. This paper elaborates on a modified version with non-integer exponent that offers more flexibility in the mathematical description. Furthermore, it outlines the implementation of this material model and similar yield criteria as user subroutines in finite element software. As mathematical flexibility increases, it enables more physically correct material approximations. However, it also becomes more challenging to calibrate because of ambiguities due to a larger number of mathematical variables. These ambiguities is demonstrated by using a Nakajima test without lubrication during inverse modeling of parameters for the BBC05 model. It shows that it is impossible to accurately identify the physically correct combination of friction coefficient and the yield surface exponent, k, using strain distributions and punch force. It is suggested to use two Nakajima tests in the inverse modeling process where friction can be neglected due to testing conforming to ISO12004-2. One test that corresponds to equi-biaxial strain of the sheet, and one that corresponds to plane strain in the transverse direction of the sheet. By utilizing these samples in the inverse modeling it is possible to separate friction from the exponent k. A non-integer value of k is found to yield the most reliable prediction of strains and forces in the simulations, thereby also demonstrating the need of flexible yield surface models such as BBC05 with non-integer exponent, YLD2000, Vegter and more advanced yield criteria.

  • 4.
    Sigvant, Mats
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Pilthammar, Johan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Hol, J.
    TriboForm Engineering, NLD.
    Wiebenga, J. H.
    TriboForm Engineering, NLD.
    Chezan, T.
    Tata Steel, NLD.
    Carleer, B.
    AutoForm Engineering, DEU.
    Van Den Boogaard, A. H.
    University of Twente, NLD.
    Friction in Sheet Metal Forming Simulations: Modelling of New Sheet Metal Coatings and Lubricants2018In: IOP Conference Series: Materials Science and Engineering, Institute of Physics Publishing , 2018, Vol. 418, no 1, article id 012093Conference paper (Refereed)
    Abstract [en]

    The quality of sheet metal formed parts is strongly dependent on the tribology and friction conditions that are acting in the actual forming process. These friction conditions are then dependent on the tribology system, i.e. the applied sheet material, coating and tooling material, the lubrication and process conditions. Although friction is of key importance, it is currently not considered in detail in sheet metal forming simulations. The current industrial standard is to use a constant (Coulomb) coefficient of friction, which limits the overall simulation accuracy. Since a few years back there is an ongoing collaboration on friction modelling between Volvo Cars, Tata Steel, TriboForm Engineering, AutoForm Engineering and the University of Twente. In previous papers by the authors, results from lab scale studies and studies of a door-inner part in Volvo Cars production have been presented. This paper focuses on the tribology conditions during early tryout of dies for new car models with an emphasis on the effect of the usage of new steel material coatings and lubricants on forming results. The motivation for the study is that the majority of the forming simulations at Volvo Cars are performed to secure the die tryout, i.e. solve as many problems as possible in forming simulations before the final design of the die and milling of the casting. In the current study, three closure parts for the new Volvo V60 model have been analysed with both Coulomb and TriboForm friction models. The simulation results from the different friction models are compared using thickness measurements of real parts, and 3D geometry scanning data of the parts. Results show the improved prediction accuracy of forming simulations when using the TriboForm friction model, demonstrating the ability to account for the effect of new sheet metal coatings and lubricants in sheet metal forming simulations. © Published under licence by IOP Publishing Ltd.

  • 5.
    Sigvant, Mats
    et al.
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Pilthammar, Johan
    Blekinge Institute of Technology, Faculty of Engineering, Department of Mechanical Engineering.
    Hol, Johan
    TriboForm Engineering, NLD.
    Wiebenga, J. H.
    TriboForm Engineering, NLD.
    Chezan, Toni
    Tata Steel Europe Limited, GBR.
    Carleer, Bart
    AutoForm Engineering, DEU.
    van den Boogaard, Ton
    University of Twente, NLD.
    Friction in sheet metal forming: Influence of surface roughness and strain rate on sheet metal forming simulation results2019In: Procedia Manufacturing, Elsevier B.V. , 2019, p. 512-519Conference paper (Refereed)
    Abstract [en]

    The quality of sheet metal formed parts is strongly dependent on the tribology and friction conditions that are acting in the actual forming process. These friction conditions are then dependent on the tribology system, i.e. the applied sheet material, coating and tooling material, the lubrication and process conditions. Although friction is of key importance, it is currently not considered in detail in sheet metal forming simulations. The current industrial standard is to use a constant (Coulomb) coefficient of friction, which limits the overall simulation accuracy. Since a few years, back there is an ongoing collaboration on friction modelling between Volvo Cars, Tata Steel, TriboForm Engineering, AutoForm Engineering and the University of Twente. In previous papers by the authors, results from lab scale studies and studies of body parts at Volvo Cars, both parts in early tryout for new car models as well as parts in production have been presented. However, the introduction of a new friction model in the sheet metal forming simulations forces the user to gain knowledge about accurate values for new input parameters and question current modeling assumptions. This paper presents results from studies on the influence on the sheet metal forming simulation results from stamping die surface roughness and introduction of strain rate sensitivity in the sheet material model. The study will use a FE-model of a part presented in previous papers. © 2019 The Authors. Published by Elsevier B.V.

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