A review of predictive nonlinear theories for multiscale modeling of heterogeneous materials

Localisation studies have been carried out for an unconstrained, elasto-plastic, strain-softening Cosserat continuum. Because of the presence of an internal length scale in this continuum model a perfect convergence is found upon mesh refinement. A finite, constant width of the localisation zone and a finite energy dissipation are computed under static as well as under transient loading conditions. Because of the existence of rotational degrees-of-freedom in a Cosserat continuum additional wave types arise and wave propagation becomes dispersive. This has been investigated analytically and numerically for an elastic Cosserat continuum and an excellent agreement has been found between both solutions.

Localisation in a Cosserat continuum under static and dynamic loading conditions

This article focuses on computational multiscale methods for the mechanical response of nonlinear heterogeneous materials. After a short historical note, a brief overview is given of some recent activities in the field, with a particular focus on nonlinear homogenization methods. The two‐scale nonlinear computational homogenization (CH) scheme for mechanics is presented, along with details on representative unit cell aspects and statistics. Model performance is advocated through a decoupled implementation and multiscale schemes based on the nonuniform transformation field analysis. High‐performance parallel multiscale implementations of the CH scheme are addressed in more detail.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/9781119176817.ecm2107

Homogenization methods and multiscale modeling : Nonlinear problems

This textbook compiles reports written by about 35 internationally recognized authorities, and covers a range of interests for geotechnical engineers. Topics include: fundamentals for mechanics of granular materials; continuum theory of granular materials; and discrete element approaches.

Mechanics of granular materials : an introduction

3D multiscale modeling of strain localization in granular media

A mixed finite element (FE) procedure of the gradient Cosserat continuum for the second-order computational homogenisation of granular materials is presented. The proposed mixed FE is developed based on the Hu---Washizu variational principle. Translational displacements, microrotations, and displacement gradients with Lagrange multipliers are taken as the independent nodal variables. The tangent stiffness matrix of the mixed FE is formulated. The advantage of the gradient Cosserat continuum model in capturing the meso-structural size effect is numerically demonstrated. Patch tests are specially designed and performed to validate the mixed FE formulations. A numerical example is presented to demonstrate the performance of the mixed FE procedure in the simulation of strain softening and localisation phenomena, while without the need to specify the macroscopic phenomenological constitutive relationship and material failure model. The meso-structural mechanisms of the macroscopic failure of granular materials are detected, i.e. significant development of dissipative sliding and rolling frictions among particles in contacts, resulting in the loss of contacts.

A mixed finite element procedure of gradient Cosserat continuum for second-order computational homogenisation of granular materials

A mixed FEM–crushable discrete-element method (DEM) nested scheme in the frame of second-order computational homogenization for granular materials was proposed. The particle breakage followed by the discontinuity and dissipative relative movements between each of two immediate neighboring particles were modeled at the mesoscale to perform both the downscaling and upscaling between the mixed FEM at the macroscopic continuum scale and the crushable DEM at the mesoscopic discrete particle assembly scale. To develop the crushable DEM for modeling the mesostructural evolution within representative volume elements (RVEs) assigned to integrating points of the macroscopic Cosserat continuum in the homogenization, two grain breakage models consisting of crushing criteria and the fracture mode for an individual crushable particle were developed. Not only the contact forces, but also contact moments exerted on each individual grain via the contacting points on the grain surface, were taken into account to se...

Mixed FEM–Crushable DEM Nested Scheme in Second-Order Computational Homogenization for Granular Materials

Computational multiscale methods for granular materials

The paper reports recent advances in multiscale modeling of granular materials, particularly in the second-order computational homogenization method and corresponding global–local mixed FEM-DEM nested analysis scheme. The gradient Cosserat continuum and the classical Cosserat continuum are assumed for modelling granular media at the macro- and meso- scales, respectively. According to the generalized Hill’s lemma formulated for the adopted meso-macro continuum modeling the non-uniform macroscopic strain field with macroscopic strain gradients is downscaled to each representative volume element (RVE), while satisfaction of the generalized Hill–Mandel condition is ensured. The advantage of the gradient Cosserat continuum model in capturing the meso-structural size effect and the performance of the proposed second-order computational homogenization in the simulation of strain softening and localization phenomena are demonstrated, without need to specify macroscopic phenomenological constitutive relationship and material failure model.

Yuanbo Liang

Papers

A mixed finite element procedure of gradient Cosserat continuum for second-order computational homogenisation of granular materials

Mixed FEM–Crushable DEM Nested Scheme in Second-Order Computational Homogenization for Granular Materials

Computational multiscale methods for granular materials

Advances in Multiscale Modeling of Granular Materials