Characterization of the Mechanical Behavior of Colorado Mason Sand at Grain-Level by Nanoindentation

Colorado Mason sand has received increasing attention for use as a model granular material for the investigation of the soil response under a blast. The grain-level mechanical properties of Colorado Mason sand, which are important input for modeling and simulation of such granular material, are measured by nanoindentation. The as-received assorted sand is sorted into six grain sizes: 0.15 mm, 0.21 mm, 0.3 mm, 0.42 mm, 0.6 mm, and 0.84 mm. The sand chemical constituents are determined using energy dispersive X-ray spectroscopy, and three main types of sand grains are determined as silica, rock, and metal oxide. The Young’s modulus and hardness are measured using nanoindentation with a Berkovich tip. A cube-corner indenter tip is used to generate radial cracks, the lengths of which are used to determine the fracture toughness. The mechanical properties (Young’s modulus, hardness and fracture toughness) of the sand are statistically analyzed, and are found to follow a tri-modal Weibull distribution, corresponding to three main types of constituent grains. The grains show ductile behavior under Berkovich tip due to confinement by high pressure induced by the tip. An inverse method is used to determine the stress-strain relationship for individual sand grains using finite element analysis, with the consideration of Drucker-Prager yield criterion. The grain-level mechanical properties determined in this study can be used in microscale and mesoscale simulations.