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Guoqiang Li - One of the best experts on this subject based on the ideXlab platform.

  • Constitutive Modeling of shape memory polymer based self healing syntactic foam
    International Journal of Solids and Structures, 2010
    Co-Authors: We Xu, Guoqiang Li
    Abstract:

    Abstract In a previous study, it was found that the shape memory functionality of a shape memory polymer based syntactic foam can be utilized to self-seal impact damage repeatedly, efficiently, and almost autonomously [Li G., John M., 2008. A self-healing smart syntactic foam under multiple impacts. Comp. Sci. Technol. 68(15–16), 3337–3343]. The purpose of this study is to develop a thermodynamics based Constitutive model to predict the thermomechanical behavior of the smart foam. First, based on DMA tests and FTIR tests, the foam is perceived as a three-phase composite with interfacial transition zone (interphase) coated microballoons dispersed in the shape memory polymer (SMP) matrix; for simplicity, it is assumed to be an equivalent two-phase composite by dispersing elastic microballoons into an equivalent SMP matrix. Second, the equivalent SMP matrix is phenomenologically assumed to consist of an active (rubbery) phase and a frozen (glassy) phase following Liu et al. [Liu, Y., Gall, K., Dunn, M.L., Greenberg, A.R., Diani J., 2006. Thermomechanics of shape memory polymers: uniaxial experiments and Constitutive Modeling. Int. J. Plasticity 22, 279–313]. The phase transition between these two phases is through the change of the volume fraction of each phase and it captures the thermomechanical behavior of the foam. The time rate effect is also considered by using rheological models. With some parameters determined by additional experimental testing, the prediction by this model is in good agreement with the 1D test result found in the literature. Parametric studies are also conducted using the Constitutive model, which provide guidance for future design of this novel self-healing syntactic foam and a class of light-weight composite sandwich structures.

Etsuko Yamada - One of the best experts on this subject based on the ideXlab platform.

Julie Diani - One of the best experts on this subject based on the ideXlab platform.

  • Constitutive Modeling of the anisotropic behavior of Mullins softened filled rubbers
    Mechanics of Materials, 2013
    Co-Authors: Yannick Merckel, Julie Diani, Mathias Brieu, Julien Caillard
    Abstract:

    Original Constitutive Modeling is proposed for filled rubber materials in order to capture the anisotropic softened behavior induced by general non-proportional pre-loading histories. The hyperelastic framework is grounded on a thorough analysis of cyclic experimental data. The strain energy density is based on a directional approach. The model leans on the strain amplification factor concept applied over material directions according to the Mullins softening evolution. In order to provide a model versatile that applies for a wide range of materials, the proposed framework does not require to postulate the mathematical forms of the elementary directional strain energy density and of the Mullins softening evolution rule. A computational procedure is defined to build both functions incrementally from experimental data obtained during cyclic uniaxial tensile tests. Successful comparisons between the model and the experiments demonstrate the model abilities. Moreover, the model is shown to accurately predict the non-proportional uniaxial stress-stretch responses for uniaxially and biaxially pre-stretched samples. Finally, the model is efficiently tested on several materials and proves to provide a quantitative estimate of the anisotropy induced by the Mullins softening for a wide range of filled rubbers.

  • Constitutive Modeling of the anisotropic behavior of Mullins softened filled rubbers
    Mechanics of Materials, 2012
    Co-Authors: Yannick Merckel, Julie Diani, Mathias Brieu, Julien Caillard
    Abstract:

    Original Constitutive Modeling is proposed for filled rubber materials in order to capture the anisotropic softened behavior induced by general non-proportional pre-loading histo-ries. The hyperelastic framework is grounded on a thorough analysis of cyclic experimental data. The strain energy density is based on a directional approach. The model leans on the strain amplification factor concept applied over material directions according to the Mul-lins softening evolution. In order to provide a model versatile that applies for a wide range of materials, the proposed framework does not require to postulate the mathematical forms of the elementary directional strain energy density and of the Mullins softening evo-lution rule. A computational procedure is defined to build both functions incrementally from experimental data obtained during cyclic uniaxial tensile tests. Successful compari-sons between the model and the experiments demonstrate the model abilities. Moreover, the model is shown to accurately predict the non-proportional uniaxial stress-stretch responses for uniaxially and biaxially pre-stretched samples. Finally, the model is effi-ciently tested on several materials and proves to provide a quantitative estimate of the anisotropy induced by the Mullins softening for a wide range of filled rubbers.

  • thermomechanics of shape memory polymers uniaxial experiments and Constitutive Modeling
    International Journal of Plasticity, 2006
    Co-Authors: Yiping Liu, Ken Gall, Martin L Dunn, Alan R Greenberg, Julie Diani
    Abstract:

    Abstract Shape memory polymers (SMPs) can retain a temporary shape after pre-deformation at an elevated temperature and subsequent cooling to a lower temperature. When reheated, the original shape can be recovered. Relatively little work in the literature has addressed the Constitutive Modeling of the unique thermomechanical coupling in SMPs. Constitutive models are critical for predicting the deformation and recovery of SMPs under a range of different constraints. In this study, the thermomechanics of shape storage and recovery of an epoxy resin is systematically investigated for small strains (within ±10%) in uniaxial tension and uniaxial compression. After initial pre-deformation at a high temperature, the strain is held constant for shape storage while the stress evolution is monitored. Three cases of heated recovery are selected: unconstrained free strain recovery, stress recovery under full constraint at the pre-deformation strain level (no low temperature unloading), and stress recovery under full constraint at a strain level fixed at a low temperature (low temperature unloading). The free strain recovery results indicate that the polymer can fully recover the original shape when reheated above its glass transition temperature ( T g ). Due to the high stiffness in the glassy state ( T T g ), the evolution of the stress under strain constraint is strongly influenced by thermal expansion of the polymer. The relationship between the final recoverable stress and strain is governed by the stress–strain response of the polymer above T g . Based on the experimental results and the molecular mechanism of shape memory, a three-dimensional small-strain internal state variable Constitutive model is developed. The model quantifies the storage and release of the entropic deformation during thermomechanical processes. The fraction of the material freezing a temporary entropy state is a function of temperature, which can be determined by fitting the free strain recovery response. A free energy function for the model is formulated and thermodynamic consistency is ensured. The model can predict the stress evolution of the uniaxial experimental results. The model captures differences in the tensile and compressive recovery responses caused by thermal expansion. The model is used to explore strain and stress recovery responses under various flexible external constraints that would be encountered in applications of SMPs.

Hisaaki Tobushi - One of the best experts on this subject based on the ideXlab platform.

Kjell Mattiasson - One of the best experts on this subject based on the ideXlab platform.

  • on Constitutive Modeling for springback analysis
    International Journal of Mechanical Sciences, 2010
    Co-Authors: Peranders Eggertsen, Kjell Mattiasson
    Abstract:

    The springback phenomenon that occurs in thin metal sheets after forming is mainly a stress driven problem, and the magnitude is roughly proportional to the ratio between residual stresses and Young's modulus. An accurate prediction of residual stresses puts, in turn, high demands on the material Modeling during the forming simulation. A phenomenological plasticity model is made up of several ingredients, such as a yield condition, a plastic hardening curve, a hardening law, and a model for the degradation of elastic stiffness due to plastic straining. The authors of this paper have recently, [1], showed the importance of a correct Modeling of a cyclic stress-strain behavior via a phenomenological hardening law, in order to obtain an accurate stress prediction. The main purposes of the present study are to study the influence of two other Constitutive ingredients: the yield criterion and the material behavior during unloading. Three different yield criteria of different complexity are evaluated in the present investigation: the Hill'48 criterion, the Barlat-Lian Y1d89 criterion, and the 8-parameter criterion by Banabic/Aretz/Barlat. The material behavior during unloading is evaluated by loading/unloading tension tests, where the material is unloaded/reloaded at specified plastic strain levels. The slope of the unloading curve is measured and a relation between the "unloading modulus" and the plastic stain is established. In the current study, results for four different materials are accounted for. The springback of a simple U-bend is calculated for all the materials in the rolling-, transverse- and diagonal directions. From the results of these simulations, some conclusions regarding Constitutive Modeling for springback simulations are drawn. (C) 2010 Elsevier Ltd. All rights reserved.

  • Oriented Damage in Ductile Sheets: Constitutive Modeling and Numerical Integration
    International Journal of Damage Mechanics, 2007
    Co-Authors: Edin Omerspahic, Kjell Mattiasson
    Abstract:

    Thermodynamics with internal variables provides a framework for Constitutive Modeling of elasto-plastic deformations. Within the scope of the theory, Constitutive and evolution equations for ductile, elasto-plastic materials with mixed (isotropic and kinematic) hardening and anisotropic damage have been developed. Postulates within continuum damage mechanics were used in order to incorporate damage as an internal variable. Owing to this, and to a simplified definition of the inverted damage effect tensor, a general expression for degradation of the elastic properties in materials has been obtained. The corresponding numerical algorithm for integration of the Constitutive equations is based on an elastic predictor – plastic/damage corrector procedure. The plastic/damage corrector is uncoupled, which further simplifies and expedites the corrector procedure.