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Philipp Junker - One of the best experts on this subject based on the ideXlab platform.

  • Variational Modeling and Finite-Element Simulation of Functional Fatigue in Polycrystalline Shape Memory Alloys
    Journal of Optimization Theory and Applications, 2019
    Co-Authors: Johanna Waimann, Klaus Hackl, Philipp Junker
    Abstract:

    Based on our previous works, we present the finite-element implementation of an energy-Based Material Model that displays the effect of functional fatigue of shape memory alloys during cyclic loading. The functional degradation is included in our Model by taking account of irreversible martensitic volume fractions. Three internal variables are used: reversible and irreversible volume fractions for the crystallographic phases and Euler angles for parametrization of the martensite strain orientation. The evolution of the volume fractions is Modeled in a rate-independent manner, whereas a viscous approach is employed for the Euler angles, which account for the Materials’ polycrystalline structure. For the case of a cyclically loaded wire, we calibrate our Model using experimental data. The calibration serves as input for the simulation of two more complex boundary value problems to demonstrate the functionality of our Material Model for localized phase transformations.

  • The effect of plasticity on damage evolution using a relaxation-Based Material Model
    Journal of the Mechanical Behavior of Materials, 2018
    Co-Authors: Stephan Schwarz, Klaus Hackl, Philipp Junker
    Abstract:

    Abstract As damage occurs in the context of high stresses that are also related to the presence of plastic strains, it is natural to investigate the effect of plasticity on damage evolution and to thus achieve a more realistic Model. In this work, the existing and new damage Model presented in [Junker P, Schwarz S, Makowski J, Hackl K. Continuum Mech. Therm. 2017, 29 (1), 291–310] is enhanced with plasticity and isotropic hardening. The damage Model is Based on a relaxation-Based approach and does not require additional complex regularization techniques besides considering viscous effects. The benefit of the Model are mesh-independent results for the rate-dependent case, even without considering, e.g. gradient terms for mathematical regularization. The enhancement with plasticity and isotropic hardening was investigated for a representative volume element that considerd a damaging matrix Material and non-damaging hard precipitates. Two different loading types, pure tension and pure shear, yielded the homogenized stress/strain response for the Material at various loading rates. Hereto, several finite discretizations in terms of finite-element meshes were used. The results underline the mesh-independence for physically reasonable loading rates and viscosities.

  • numerical study of the plasticity induced stabilization effect on martensitic transformations in shape memory alloys
    The International Conference on Shape Memory and Superelastic Technologies (SMST) May 15 - 19 2017, 2017
    Co-Authors: Philipp Junker, Philipp Hempel
    Abstract:

    It is well known that plastic deformations in shape memory alloys stabilize the martensitic phase. Furthermore, the knowledge concerning the plastic state is crucial for a reliable sustainability analysis of construction parts. Numerical simulations serve as a tool for the realistic investigation of the complex interactions between phase transformations and plastic deformations. To account also for irreversible deformations, we expand an energy-Based Material Model by including a non-linear isotropic hardening plasticity Model. An implementation of this Material Model into commercial finite element programs, e.g., Abaqus, offers the opportunity to analyze entire structural components at low costs and fast computation times. Along with the theoretical derivation and expansion of the Model, several simulation results for various boundary value problems are presented and interpreted for improved construction designing.

  • Calibration and Finite Element Implementation of an Energy-Based Material Model for Shape Memory Alloys
    Shape Memory and Superelasticity, 2016
    Co-Authors: Philipp Junker, Klaus Hackl
    Abstract:

    Numerical simulations are a powerful tool to analyze the complex thermo-mechanically coupled Material behavior of shape memory alloys during product engineering. The benefit of the simulations strongly depends on the quality of the underlying Material Model. In this contribution, we discuss a variational approach which is Based solely on energetic considerations and demonstrate that unique calibration of such a Model is sufficient to predict the Material behavior at varying ambient temperature. In the beginning, we recall the necessary equations of the Material Model and explain the fundamental idea. Afterwards, we focus on the numerical implementation and provide all information that is needed for programing. Then, we show two different ways to calibrate the Model and discuss the results. Furthermore, we show how this Model is used during real-life industrial product engineering.

  • A condensed variational Model for thermo-mechanically coupled phase transformations in polycrystalline shape memory alloys
    Journal of the Mechanical Behavior of Materials, 2013
    Co-Authors: Philipp Junker, Klaus Hackl
    Abstract:

    AbstractWe derive an energy-Based Material Model for thermomechanically coupled phase transformations in polycrystalline shape memory alloys. For the variational formulation of the Model, we use the principle of the minimum of the dissipation potential for nonisothermal processes for which only a minimal number of constitutive assumptions has to be made. By introducing a condensed formulation for the representative orientation distribution function, the resulting Material Model is numerically highly efficient. For a first analysis, we present the results of Material point calculations, where the evolution of temperature as well as its influence on the mechanical Material response is investigated.

Klaus Hackl - One of the best experts on this subject based on the ideXlab platform.

  • Variational Modeling and Finite-Element Simulation of Functional Fatigue in Polycrystalline Shape Memory Alloys
    Journal of Optimization Theory and Applications, 2019
    Co-Authors: Johanna Waimann, Klaus Hackl, Philipp Junker
    Abstract:

    Based on our previous works, we present the finite-element implementation of an energy-Based Material Model that displays the effect of functional fatigue of shape memory alloys during cyclic loading. The functional degradation is included in our Model by taking account of irreversible martensitic volume fractions. Three internal variables are used: reversible and irreversible volume fractions for the crystallographic phases and Euler angles for parametrization of the martensite strain orientation. The evolution of the volume fractions is Modeled in a rate-independent manner, whereas a viscous approach is employed for the Euler angles, which account for the Materials’ polycrystalline structure. For the case of a cyclically loaded wire, we calibrate our Model using experimental data. The calibration serves as input for the simulation of two more complex boundary value problems to demonstrate the functionality of our Material Model for localized phase transformations.

  • The effect of plasticity on damage evolution using a relaxation-Based Material Model
    Journal of the Mechanical Behavior of Materials, 2018
    Co-Authors: Stephan Schwarz, Klaus Hackl, Philipp Junker
    Abstract:

    Abstract As damage occurs in the context of high stresses that are also related to the presence of plastic strains, it is natural to investigate the effect of plasticity on damage evolution and to thus achieve a more realistic Model. In this work, the existing and new damage Model presented in [Junker P, Schwarz S, Makowski J, Hackl K. Continuum Mech. Therm. 2017, 29 (1), 291–310] is enhanced with plasticity and isotropic hardening. The damage Model is Based on a relaxation-Based approach and does not require additional complex regularization techniques besides considering viscous effects. The benefit of the Model are mesh-independent results for the rate-dependent case, even without considering, e.g. gradient terms for mathematical regularization. The enhancement with plasticity and isotropic hardening was investigated for a representative volume element that considerd a damaging matrix Material and non-damaging hard precipitates. Two different loading types, pure tension and pure shear, yielded the homogenized stress/strain response for the Material at various loading rates. Hereto, several finite discretizations in terms of finite-element meshes were used. The results underline the mesh-independence for physically reasonable loading rates and viscosities.

  • Calibration and Finite Element Implementation of an Energy-Based Material Model for Shape Memory Alloys
    Shape Memory and Superelasticity, 2016
    Co-Authors: Philipp Junker, Klaus Hackl
    Abstract:

    Numerical simulations are a powerful tool to analyze the complex thermo-mechanically coupled Material behavior of shape memory alloys during product engineering. The benefit of the simulations strongly depends on the quality of the underlying Material Model. In this contribution, we discuss a variational approach which is Based solely on energetic considerations and demonstrate that unique calibration of such a Model is sufficient to predict the Material behavior at varying ambient temperature. In the beginning, we recall the necessary equations of the Material Model and explain the fundamental idea. Afterwards, we focus on the numerical implementation and provide all information that is needed for programing. Then, we show two different ways to calibrate the Model and discuss the results. Furthermore, we show how this Model is used during real-life industrial product engineering.

  • A condensed variational Model for thermo-mechanically coupled phase transformations in polycrystalline shape memory alloys
    Journal of the Mechanical Behavior of Materials, 2013
    Co-Authors: Philipp Junker, Klaus Hackl
    Abstract:

    AbstractWe derive an energy-Based Material Model for thermomechanically coupled phase transformations in polycrystalline shape memory alloys. For the variational formulation of the Model, we use the principle of the minimum of the dissipation potential for nonisothermal processes for which only a minimal number of constitutive assumptions has to be made. By introducing a condensed formulation for the representative orientation distribution function, the resulting Material Model is numerically highly efficient. For a first analysis, we present the results of Material point calculations, where the evolution of temperature as well as its influence on the mechanical Material response is investigated.

Manfred Klüppel - One of the best experts on this subject based on the ideXlab platform.

  • a physically Based Model of stress softening and hysteresis of filled rubber including rate and temperature dependency
    International Journal of Plasticity, 2017
    Co-Authors: J. Plagge, Manfred Klüppel
    Abstract:

    Abstract A novel physically Based Material Model is presented that describes the complex stress-strain behavior of filled rubbers under arbitrary deformation histories in a constitutive manner. The polymer response is considered by the extended non-affine tube Model. Stress softening is taken into account via the breakdown of highly stressed polymer-filler domains under load and homogenization of the medium. Set stress and hysteresis are introduced via a continuous reformation mechanism, characterized by a single critical stress parameter. The latter is predicted to be dependent on temperature and deformation rate by means of Kramers escape rate. This is confirmed for a wide range of temperatures and speeds by fitting to multihysteresis measurements carried out in a heat chamber. Fitting parameters reveal that the mechanism responsible for hysteresis and set stress takes place on the nanometer scale with energies of roughly 100 kJ/mol. The behavior of the fitting parameters is analyzed for varying filler loadings and crosslinker concentrations in EPDM. Simulations of the stress-strain response for several deformation modes are in good agreement with experiments and its mathematical simplicity makes it very promising for applications with Finite Element Methods (FEM).

  • Finite element implementation of a microstructure-Based Model for filled elastomers
    International Journal of Plasticity, 2011
    Co-Authors: M. Freund, H. Lorenz, Daniel Juhre, Jörn Ihlemann, Manfred Klüppel
    Abstract:

    To describe the inelastic mechanical behavior of filled elastomers a microstructure-Based Material Model for uniaxial loadings has been developed. The generalization of this one-dimensional Material description to a fully three-dimensional constitutive Model has been accomplished by using the concept of representative directions. The generalized Model shows a very good agreement with cyclic uniaxial tension and compression tests as well as simple shear measurements for several rubber compounds. The FE-implementation enables finite element simulations of technical components though the original input Model predicts the Material behavior for uniaxial loadings only.

Yung C Shin - One of the best experts on this subject based on the ideXlab platform.

  • dislocation density Based Modeling of subsurface grain refinement with laser induced shock compression
    Computational Materials Science, 2012
    Co-Authors: Hongtao Ding, Yung C Shin
    Abstract:

    Abstract Laser shock peening (LSP) is an innovative surface treatment technique applied to improve the mechanical properties and surface microstructures of metallic components. This paper is concerned with prediction of the microstructural evolution of metallic components subjected to single or multiple LSP impacts. A numerical framework is developed to Model the evolution of dislocation density and dislocation cell size using a dislocation density-Based Material Model. It is shown that the developed Model captures the essential features of the Material mechanical behaviors and predicts that the total dislocation density reaches the order of 1014 m−2 and a minimum dislocation cell size is below 250 nm for LSP of monocrystalline coppers using the laser energy density on the order of 500 GW/cm2. It is further shown that the Model is cable of predicting the Material strengthening mechanism in terms of residual stress and microhardness of the LY2 aluminum alloy due to grain refinement in a LSP process with less laser energy densities on the order of several GW/cm2.

  • Predictive Modeling of grain refinement during multi-pass cold rolling
    Journal of Materials Processing Technology, 2012
    Co-Authors: Hongtao Ding, Ninggang Shen, Yung C Shin
    Abstract:

    Abstract Recently, grain refinement and grain misorientation have been experimentally studied for various Materials with ultra-fine grained microstructures, which are achieved by the multi-pass cold rolling process. In this paper, a numerical framework is developed to Model the evolution of grain size and grain misorientation Based on a dislocation density-Based Material Model. Novel finite element Models embedded with the dislocation density-Based Material subroutine are developed to Model the plastic deformation and microstructural evolution during the multi-pass cold rolling process. The multi-pass cold rolling processes of commercially pure titanium (CP Ti) and aluminum (AA 1200) are simulated in order to assess the validity of the numerical solution through comparison with experiments. The dislocation density-Based Material Models are developed for CP Ti and AA 1200, which reproduce the observed Material constitutive mechanical behavior under various strains, strain rates and temperatures occurring in the cold rolling process. It is shown that the developed Model captures the essential features of the Material mechanical behaviors and predicts a minimum grain size of below 100 nm after five-pass cold rolling of CP Ti with equivalent strains up to 2.07 and the average incidental dislocation boundary (IDB) misorientation angle increased to 4.6° after six-pass cold rolling of AA 1200 with equivalent strains accumulated to 5.77.

Sofia Hansson - One of the best experts on this subject based on the ideXlab platform.