X-ray tomography analysis of particle morphology influence on granular deformation processes

The interaction between particles in granular materials is largely determined by their shape and interparticle friction. Thus, understanding their combined effects is essential for modelling the mechanical behaviour at the bulk scale. Previous studies have focused on the link between the morphology of the particles and the bulk response of the specimen. The emergence of non destructive full-field techniques, such as x-ray tomography, present a novel opportunity for the detailed quantification of key particle-scale phenomena. This study investigates the impact of inter-particle friction and particle shape on the deformation processes of granular materials through in-operando x-ray tomography. Monodisperse specimens, comprising ellipsoidal particles with a given aspect ratio and interparticle friction coefficients, are here tested under triaxial compression conditions. Three values of aspect ratio and two friction coefficients are explored, yielding in total six specimens. Over 30 scans per test are acquired, every 0.5 % of axial shortening. Each of the more than 20000 individual particles are identified and tracked throughout a test. Strain localisation dominates post-peak stress ratio, forming compressive and dilative zones within the shear band. The results show that higher aspect ratios lead to an increase of volumetric strain, while lower interparticle friction makes the response less dilative. The study of the interplay between particles interlocking and rotation, reveals that particles with a mild degree of anisometry and high friction yield the highest degree of bulk dilatancy, due to a balancing between the interlocking and rotation.