A density dependent Drucker-Prager/Cap model for ring shear simulation of ground loblolly pine

Abstract

Integrated biorefineries suffer from equipment down-time due to poor understanding of the flowability of biomass-derived feedstock. This work presents the characterization of the mechanical behavior of ground loblolly pine by combining physical experiments and numerical simulations. A modified Drucker-Prager/Cap (MDPC) model enhanced with density dependence is used for finite element modeling. Cyclic oedometer tests with increased magnitude of compressive stress and Schulze ring shear tests are performed to characterize material compressibility and shear behavior. The laboratory tests yield stress-strain curves, density-stress curves and Mohr-Coulomb shear envelopes, which are then used directly and indirectly to calibrate elasticity, as well as cap and shear failure parameters of the MDPC model. Full size 3D Schulze ring shear tests are modeled in Abaqus with calibrated model parameters, and the simulated Mohr-Coulomb envelops match well against experimental results, indicating the stress state within the shear band of the ring shear test is close to triaxial compression. The modeling results also show the MDPC model does not predict dilation followed by constant volume as observed by experiments. The mechanical behavior derived from the experiments and the methodology proposed for model calibration and stress state characterization provide a foundation for studying biomass flow behavior in material feeding and handling equipment.