TY  - JOUR
A1  - Wang, Lei
A1  - Dresen, Georg
A1  - Rybacki, Erik
A1  - Bonnelye, Audrey
A1  - Bohnhoff, Marco
T1  - Pressure-dependent bulk compressibility of a porous granular material modeled by improved contact mechanics and micromechanical approaches
BT  - effects of surface roughness of grains
JF  - Acta materialia
N2  - The change of the mechanical properties of granular materials with pressure is an important topic associated with many industrial applications. In this paper we investigate the influence of hydrostatic pressure (P-e) on the effective bulk compressibility (C-eff) of a granular material by applying two modified theoretical approaches that are based on contact mechanics and micromechanics, respectively. For a granular material composed of rough grains, an extended contact model is developed to elucidate the effect of roughness of grain surfaces on bulk compressibility. At relatively low pressures, the model predicts that the decrease of bulk compressibility with pressure may be described by a power law with an exponent of -1/2 (i.e., C-eff proportional to P-e(1/2) ), but deviates at intermediate pressures. At elevated pressures beyond full contact, bulk compressibility remains almost unchanged, which may be roughly evaluated by continuum contact mechanics. As an alternative explanation of pressure-dependent bulk compressibility, we suggest a micromechanical model that accounts for effects of different types of pore space present in granular materials. Narrow and compliant inter-granular cracks are approximated by three-dimensional oblate spheroidal cracks with rough surfaces, whereas the equant and stiff pores surrounded by three and four neighboring grains are modeled as tubular pores with cross sections of three and four cusp-like corners, respectively. In this model, bulk compressibility is strongly reduced with increasing pressure by progressive closure of rough-walled cracks. At pressures exceeding crack closure pressure, deformation of the remaining equant pores is largely insensitive to pressure, with almost no further change in bulk compressibility. To validate these models, we performed hydrostatic compression tests on Bentheim sandstone (a granular rock consisting of quartz with high porosity) under a wide range of pressure. The relation between observed microstructures and measured pressure-dependent bulk compressibility is well explained by both suggested models.
KW  - Bulk compressibility
KW  - Granular materials
KW  - Roughness
KW  - Micromechanical model
KW  - Contact model
Y1  - 2020
U6  - https://doi.org/10.1016/j.actamat.2020.01.063
SN  - 1359-6454
SN  - 1873-2453
VL  - 188
SP  - 259
EP  - 272
PB  - Elsevier
CY  - Amsterdam
ER  -