Understanding the mechanical behavior of sand is critical to develop constitutive models to simulate the ejecta in soil under blast, especially under relatively high stress and high strain rates. Multi-scale simulations require accurate constitutive data for sand under high strain rates encompassing a wide range of loading conditions. In this work, a poorly-graded natural Mason sand (Colorado Materials, Longmont, CO) was chosen to investigate the biaxial mechanical behavior. An 80-ft modified long split Hopkinson pressure bar (SHPB) was modified to generate combined compression and shear loading. A self-designed loading fixture was developed to apply dynamic shear loading while the sample is under compression. The fixture consists of an incident plate, a transmission plate, and a square beam frame to provide compression. Mason sand grains were placed inside the cylindrical cavity, and capped by piston steel rods. Through tightening a pair of steel bolts constrained by a steel frame, a static compression was applied on sand. The dynamic shearing was applied directly on the narrow cylindrical sand specimen, through dynamic compression of bars on SHPB. The fixture with sand specimen was sandwiched between incident and transmission bar ends for dynamic shearing. Strain gages were attached to the frame to measure and monitor the compressive load. The as-received Mason sand was characterized at high strain rates to determine the shear behavior under different compressions. The dynamic bi-axial data was analyzed using the Drucker-Prager cap model. The experiments provide constitutive data for simulations to understand the dynamic behavior of soil under blast under high pressure and high rate deformations.
Keywords: Long split Hopkinson pressure bar, Mason sand, static compression, dynamic shear, Drucker-Prager cap model