Macro–micro responses of crushable granular materials in simulated true triaxial tests

Abstract

This paper presents simulations of true triaxial tests on crushable granular materials. Considering both the shear and tensile fracture modes of the particle, the MohrCoulomb model with tension cut-off is employed as the fracture criterion of single particle. When the particle stresses satisfy the fracture criterion, three new balls are generated to replace the broken particle. The new balls overlap enough within the bounding parent sphere to obey the mass conservation law. A polydisperse assembly consisting of 7935 spheres was isotropically compressed until the desired confining pressure was reached. Then the sample with no bias in initial fabric was subjected to axial compression at a constant minor principal stress under different intermediate principal stress ratios, b. The simulated stress-strain-dilation responses were in agreement with the experimental observations. The macro-micro responses including stress-strain characteristics, fabric tensors, anisotropies, the orientation tensor and force chain characteristics were discussed in details. It is shown that volumetric responses is affected by b. The anisotropies vary with b, but a unique macro-micro linkage exists between the anisotropies and stress ratio, q/ p, irrespective of the value of b. A linear relationship is found between the obliquity of σ 1 /σ 3 and the strength indicator (β = ln(τ 1 /τ 3 )) using the orientation tensor method.

Macroscopic softening in granular materials from a mesoscale perspective

“…The micro-and mesoscale information can help understand the underlying mechanisms behind macroscopic observations and incorporate more physics in constitutive modeling. The microscopic scale investigations focus on individual particle kinematics and contact dynamics, in some cases particle breakage is considered (Ma et al, 2014(Ma et al, , 2017Yin et al, 2016;Zhou et al, 2015); while at the mesoscopic scale, structural features are accounted for with clusters of a few particles such as force chains and grain loops (in 2D) (Tordesillas et al, 2010;Zhu et al, 2016b). These two types of mesostructures can stand as the dual characteristics of granular contact systems (Radjai et al, 1996(Radjai et al, , 1998.…”

The influence of particle-size distribution on critical state behavior of spherical and non-spherical particle assemblies

“…As seen in Fig. 12, the critical stress ratio for samples with either spherical or clumped particles can be fitted by straight lines with different slopes, indicating that the critical state ratio is only affected by the particle shape via OR, but is independent of the PSD, initial [11,37,[64][65][66] and laboratory experiments [15,19,67,68]. In particular, as shown in [19], the critical friction angle ϕcs can be linearly correlated with the shape parameters such as roundness R (roundness) or overall regularity OR.…”

Three-dimensional bonded-cell model for grain fragmentation

“…These models can be classified at least in two main groups. The first group, which we call Replacing Method, consists in substituting each broken particle when typically a load threshold is reached by a set of smaller particles [16,61]. However, a nonconservation of mass and volume may occur as the replacements are made and artificial overlapping between particles is sometimes allowed, producing local elastic overstresses.…”