Modeling micro-damage in granular solids

This paper presents a computational micromechanics modeling approach to predict damage-induced mechanical response of asphalt mixtures. Heterogeneous geometric characteristics and inelastic mechanical behavior were taken into account by introducing finite element modeling techniques and a viscoelastic material model. The modeling also includes interface fracture to represent crack growth and damage evolution. The interface fracture is modeled by using a micromechanical nonlinear viscoelastic cohesive-zone constitutive relation. Fundamental material properties and fracture characteristics were measured from simple laboratory tests and then incorporated into the model to predict rate-dependent viscoelastic damage behavior of the asphalt mixture. Simulation results demonstrate that each model parameter significantly influences the mechanical behavior of the overall asphalt mixture. Within a theoretical framework of micromechanics, this study is expected to be suitable for evaluating damage-induced performance of asphalt mixtures by measuring only material properties and fracture properties of each mix component and not by recursively performing expensive laboratory tests that are typically required for continuum damage mechanics modeling.

Granular Matter, 2002

We present a two-dimensional model of heterogeneous cohesive frictional solids where the material structure is idealized by a discrete granular particle assembly. Our discrete model is composed of convex polygons which are linked together by simple beams accounting for cohesive effects. Varying its parameters the model naturally interpolates between a continuous solid state and a discontinuous dry granular state of the material. We performed simulations of the quasi-static uniaxial loading with two different boundary conditions, and shearing of a solid. To provide a geometrical description of the damage state, and of the microscopic fracture events, different characteristic quantities will be introduced and their relevance will be examined. The results obtained from simulations are in satisfactory agreement with experimental observations.

This paper investigated the fracture behavior of asphalt mixture using randomly generated two-dimensional (2-D) microstructure models. Asphalt mixture was modeled as a multi-phase heterogeneous material with both adhesive and cohesive failure potential. Viscoelastic properties were assigned to asphalt binder. Two different fracture models, cohesive zone model (CZM) and extended finite element model (XFEM), were adopted to simulate the fracture damage within the Fine Aggregate Matrix (FAM) (cohesive failure) and at the FAM-aggregate interface (adhesive failure), respectively. The numerical simulation offers both qualitative and quantitative results to understand the fracture behavior of asphalt mixture considering the interaction between cohesive and adhesive failure. Parametric studies were conducted to evaluate the effect of loading rate, FAM modulus, and fracture parameters on fracture potential of asphalt mixture. This study provides an effective method to study the fracture mechanism of heterogeneous material by considering different fracture mechanisms for matrix material and bi-material interface.

2015

Computational microstructure models have been actively pursued by the pavement mechanics community as a promising and advantageous alternative to limited analytical and semi-empirical modeling approaches. The primary goal of this research is to develop a computational microstructure modeling framework that will eventually allow researchers and practitioners of the pavement mechanics community to evaluate the effects of constituents and mix design characteristics (some of the key factors directly affecting the quality of the pavement structures) on the mechanical responses of asphalt mixtures. To that end, the mixtures are modeled as heterogeneous materials with inelastic mechanical behavior. To account for the complex

Journal of Materials in Civil Engineering, 2004

Asphalt concrete is a heterogeneous material composed of aggregates, binder cement, and air voids, and may be described as a cemented particulate system. The load carrying behavior of such a material is strongly related to the local load transfer between aggregate particles, and this is taken as the microstructural response. Simulation of this material behavior was accomplished using a finite element technique, which was constructed to simulate the micromechanical response of the aggregate/binder system. The model incorporated a network of special frame elements with a stiffness matrix developed to predict the load transfer between cemented particles. The stiffness matrix was created from an approximate elasticity solution of the stress and displacement field in a cementation layer between particle pairs. A damage mechanics approach was then incorporated with this solution, and this lead to the construction of a softening model capable of predicting typical global inelastic behaviors found in asphalt materials. This theory was then implemented within the ABAQUS finite element analysis code to conduct simulations of particular laboratory specimens. Experimental verification of the elastic response has included tests on specially prepared cemented particulate systems, which allowed detailed measurement of aggregate displacements and rotations using video imaging and computer analysis. Model simulations compared favorably with these experimental results. Additional simulations including inelastic behavior of laboratory indirect tension tests have been conducted, and while preliminary in nature these results also compared well with experimental data.

EPJ Web of Conferences, 2021

A novel type of damageable cohesive law is presented for paired particle interactions in a DEM granular arrangement. It is designed in the spirit of a mixed breakage criterion for solid cohesion interaction, which can be implemented in parallel to a granular-frictional contact law. The evolution of damage at the contact level can be be easily modulated to enable a progressive transition from an initially linear elastic response to a loss of cohesion, by using a single parameter χ*. In a straightforward numerical implementation, the effect of this contact model is presented for a 3D periodic boundary condition DEM code. The results from a series of simulations show that, for a constant peak resistance of the cohesion, a more progressive damage result in an increase of the peak stress in a particle assembly, as well as a continuous transition in the stiffness of the stress-strain response around the peak stress.

International Journal for Numerical and Analytical Methods in Geomechanics, 2006

This study presents a finite element (FE) micromechanical modelling approach for the simulation of linear and damage-coupled viscoelastic behaviour of asphalt mixture. Asphalt mixture is a composite material of graded aggregates bound with mastic (asphalt and fine aggregates). The microstructural model of asphalt mixture incorporates an equivalent lattice network structure whereby intergranular load transfer is simulated through an effective asphalt mastic zone. The finite element model integrates the ABAQUS user material subroutine with continuum elements for the effective asphalt mastic and rigid body elements for each aggregate. A unified approach is proposed using Schapery non-linear viscoelastic model for the rateindependent and rate-dependent damage behaviour. A finite element incremental algorithm with a recursive relationship for three-dimensional (3D) linear and damage-coupled viscoelastic behaviour is developed. This algorithm is used in a 3D user-defined material model for the asphalt mastic to predict global linear and damage-coupled viscoelastic behaviour of asphalt mixture.

This paper presents a computational microstructure model to predict the fracture-related behavior of heterogeneous and inelastic asphalt mixtures. In addition to the consideration of the complex geometric characteristics and inelastic behavior of the mixtures, this study uses the cohesive zone law to simulate fracture as a gradual and rate-dependent phenomenon in which the initiation and propagation of discrete cracks take place in different locations of the mixture microstructure. Rate-dependent cohesive zone fracture properties are obtained using a procedure that combines laboratory tests of semi-circular bending specimens of a fine aggregate matrix (FAM) mixture and their numerical simulations. To address the rate-dependent fracture characteristics of the FAM phase, a rate-dependent cohesive zone model is developed and incorporated into the mainframe of ABAQUS in the form of a customized user element (UEL) subroutine. The applicability of the model is presented via microstructural simulations of a two-phase asphalt concrete mixture. The results presented in this paper imply that a computational microstructure model such as the one herein can be a good tool to enhance materials selection, mixture design and structural design of pavements, since it provides better insight into the linkage between components, mixture, and structure.

European Journal of Mechanics - A/Solids, 2009

The strength of granular media is characterized by the influence of the mean stress which is typical of frictional materials. The aim of the paper is to link the strength of the interfaces between grains and the strength of the granular assembly. The later is viewed as a porous polycrystal. A generalized selfconsistent scheme in which the grain is represented by a rigid core surrounded by a deformable interface is developed. First, the linear elastic effective behavior is considered. Then, assuming that the failure of the interfaces is ductile, the effective strength is determined by means of non-linear homogenization techniques. Finally, the case of brittle interfaces is also considered. It is shown that the nature of failure is controlled by the porosity.

Interface bonding in pavement layers is no different from other interface problems; it stems from the relationship between friction and adhesives. From a numerical point of view, any constitutive model used to explain this phenomenon should include the basic characteristics of friction with or without cohesion at the interface level. Similar interface problems have long been considered in geotechnical and structural applications.