Exploring particle roughness and anisotropy effect in direct shear loading

  • Couture, Cyrille (Port and Airport Research Institute (PARI))
  • Takano, Daiki (Port and Airport Research Institute (PARI))

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The geometry of individual particles plays an essential role on the organization, stability and evolution of the contact network in granular media. Increasingly advanced discrete elements based numerical methods have been developed to account for the complex geometrical aspects present at the particle scale and bellow. Even in such modelling approach, accurate homogenization techniques are necessary to limit the computational cost of taking into account smaller length scales, at which fractal asperities are present in natural granular media [1]. A greater understanding of the relation between selected geometrical metrics and granular mechanics is necessary for developing simplified yet realistic contact models [2]. Our objective is to study the effect of idealized particle geometries prescribed at relatively independent scales and assess their complementary and joined role on the collective deformation process governing the mechanical response. In this communication, we first present direct shear experiments performed on 3D printed particles, where the aspect ratio (AR) of oblong ellipsoids and a controlled roughness are prescribed using spherical harmonics [3]. The loading apparatus is installed inside an X-ray scanner to track the kinematics of individual particle during the loading phase. Our results show a non linear effect of AR on the mechanical response and the contribution of particle roughness. We further aim to provide insights between the assembly behavior and the development of localized zones, dilatancy and particle rotation. The shear band thickness is also seen to depend on the stability of granular contacts and evolve according to the particle shape and roughness. We present a comparison with DEM simulations, where the initial state and loading program reflect the experimental conditions. In these simulations, the particle shape are either modeled as part of the contact law or by enriching the geometrical shape of individual particles.