Discrete-continuum Multiscale Modeling Of Sand Incorporating The Particle Shape And Thermo-mechanical Effect

Granular materials are ubiquitous as the second-most media after water in nature,but there is still limited investigation into the mechanism of the granular materials.Being between the solid,liquid and gas phases,the typical granular materials,sand can reveal complicated physical and mechanical properties,which may be affected by macroscopic and microscopic factors,such as the boundary condition settings,external loadings,especially for particle shape and the chemical components within the interaction of particles.Great efforts have been dedicated to the theoretical development and computational method optimization of sand materials regarding length scales.However,continuum or discrete theories may suffer from inherent drawbacks towards the granular simulation.In this work,a new hierarchical multiscale and multifield framework is proposed with full consideration of the particle shape effect,deformation mechanism and strength of sand materials.The novel multiscale framework aims to give insight into the relationship between the macroscopic mechanical response and the internal or shear-induced anisotropy evolution for sand materials.Major work and findings are summarised below,(1)A super-ellipsoidal-DEM model is developed to establish the numerical relationship between the particle shape and the angle of repose for sand.Moreover,an analytical relationship is also given regarding the influence of particle shape on the at-rest earth pressure coefficient.Results indicate a reverse effect from particle aspect ratio and angularity on the angle of repose or at-rest earth pressure coefficient.The angle of repose depends more on the anisotropy of particle orientation than the anisotropy of contact normal,but vice versa for the at-rest earth pressure coefficient.The analytical relationship between the at-rest earth pressure coefficient and the fabric measures within the stress-force-fabric framework is verified for regular and irregular particle shapes.(2)A hierarchical multiscale framework consisting of material point method and discrete element method solvers is proposed for the sand materials.The material point method component,strengthened by the high-order interpolation technique and DEM-enriched contact algorithm,serves as the solver for boundary value problems,especially for boundary settings involving irregular geometrical shapes and materials with significant differences in stiffness.(3)The discrete element member of multiscale framework is integrated with the non-spherical particle shape and advanced contact model to characterize the non-linear behaviour of sand.The sphere cap DEM particle shape aiming for the realistic sand shape is established,compromising the numerical accuracy and computational cost.Plastic and elastic bond contact models are developed for spherical and non-spherical shapes,respectively.The influence of the external loading on the internal and induced anisotropy of sand materials are explored with the help of biaxial shear tests and rigid footing simulations.(4)The primitive multiscale framework is further extended with features of thermo-mechanical coupling and phase-transition characterization.The phase transition is fully considered at both RVE and continuum scales to characterize the deterioration of the strength of sand materials.This framework is benchmarked and verified against a series of numerical examples.As a showcase of potential engineering-scale applications,this study simulates thawinginduced slope sliding triggered by heating boundary conditions.The results demonstrate the efficiency of this framework in coping with practical engineering problems.