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This paper aims to model the effect of different shapes of inclusions on the homogenized viscoelastic properties of composite materials made of a viscoelastic matrix and inclusion particles. The viscoelastic behavior of the matrix phase is modeled by the Generalized Maxwell rheology. The effective properties are firstly derived by combining the homogenization theory of elasticity and the correspondence principle. Then, the effective rheological properties in time space are explicitly derived without using the complex inverse Laplace–Carson transformation (LC). Closed-form solutions for the effective bulk and shear rheological viscoelastic properties, the relaxation and creep moduli as well as the Poisson ratio are obtained for the isotropic case with random orientation distribution and different shapes of inclusions: spherical, oblate and elongate inclusions. The developed approach is validated against the exact solutions obtained by the classical inverse LC method. It is observed that the homogenized viscoelastic moduli are highly sensitive to different shapes of inclusions.

Long‐term creep compliance is one of the most important mechanical properties for evaluating the long‐term behavior of concrete structures. This paper aims to optimize machine‐learning models to predict this viscoelastic property. The most relevant dataset available in the literature is considered, cleaned, and preprocessed to optimize the outcome. The advanced XGBoost model, which is to be the most effective shallow machine‐learning model for modeling tabular datasets, is employed in this study to maximize model accuracy. Short‐term creep compliances of a given sample at typical ages are used as input features to model the long‐term creep compliance of concrete. This approach outperforms standard machine‐learning approaches that do not include short‐term creep as an input feature. Indeed, the short‐term behavior of concrete strongly influents its long‐term one. The optimized machine model presented herein is accurate and useful for practical applications. It uses input features that are easy to obtain to predict long‐term creep compliance up to several decades, which is difficult and expensive to measure. [ABSTRACT FROM AUTHOR]

We show that the effective behavior of composites made of viscoelastic rheological constituents can be modeled by a rheology of which the internal properties can be quasi-analytically determined from the volume fractions and rheological properties of the phases. A three-chain generalized Maxwell rheology can be used to model the behavior of a matrix-inclusion system of which both matrix and inclusions are described by the Zener rheology. Validations against exact results of the inverse Laplace–Carson are realized for a large range of the contrast between the phases. The developed solutions cover the existent solutions of the case of Maxwellian constituents. [ABSTRACT FROM AUTHOR]

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This study provides an asymptotic generalized self-consistent scheme for viscoelastic composites. The effective rheological properties are derived without using the inverse Laplace–Carson transform. It is shown that a viscoelastic composite made of a viscoelastic matrix and elastic inclusions can be perfectly represented by the same rheology of the matrix of which the effective rheological properties are functions of the viscoelastic properties of the matrix and the volume fraction as well as the elastic moduli of the inclusions. The solutions obtained herein can be also employed to study viscoelastic composites containing multi-coated inclusions or inclusions with imperfect interfaces. [ABSTRACT FROM AUTHOR]

The objective of this study is to model the effective anisotropic elastic properties of porous hydroxyapatite, wet collagen, and cortical bone by an advanced homogenization scheme with a percolation threshold concept. The theoretical basis of the anisotropic homogenization theory is first presented. A homogenization scheme with a percolation threshold concept is then introduced and validated against experimental data for porous hydroxyapatite as well as bone after decollagenization. It is also validated on a porous collagen that is a result of the demineralization of bone. Even though aligned collagen fibers are considered, similar values of the elastic stiffnesses C 11 and C 33 were found for demineralized bone due to its very high porosity. Finally the proposed method is used to model cortical bone as a mixture of hydroxyapatite mineral and soft organic content that is in turn a mixture of collagen fiber and pores filled by water. Good agreement between modeled and measured data is observed. The model presented herein is simpler than existing multi-scale homogenization schemes in the literature, but its results fit very well with the experimented trends. [ABSTRACT FROM AUTHOR]