Effect of Young’s Modulus and Surface Roughness on the Inter-Particle Friction of Granular Materials

Abstract

In the study we experimentally examine the influence of elastic properties and surface morphology on the inter-particle friction of natural soil grains. The experiments are conducted with a custom-built micromechanical apparatus and the database is enhanced by testing engineered-reference grains. Naturally-occurring geological materials are characterized by a wide spectrum of mechanical properties (e.g., Young’s modulus) and surface morphology (e.g., roughness), whereas engineered grains have much more consistent characteristics. Comparing to engineered materials, geological materials are found to display more pronounced initial plastic behavior during compression. Under the low normal load range applied in the study, between 1 and 5 N, we found that the frictional force is linearly correlated with the applied normal load, but we acknowledge that the data are found more scattered for natural soil grains, especially for rough and weathered materials which have inconsistent characteristics. The inter-particle coefficient of friction is found to be inversely correlated with the Young’s modulus and the surface roughness. These findings are important in geophysical and petroleum engineering contents, since a number of applications, such as landslides and granular flows, hydraulic fracturing using proppants, and weathering process of cliffs, among others, can be simulated using discrete numerical methods. These methods employ contact mechanics properties at the grain scale and the inter-particle friction is one of these critical components. It is stressed in our study that friction is well correlated with the elastic and morphological characteristics of the grains.

Effect of Grain Size and Surface Roughness on the Normal Coefficient of Restitution of Single Grains

“…Commercially available glass balls of three different sizes i.e., 2, 3 and 4 mm in diameter were used as grains. Sandeep and Senetakis [20] obtained the Young's modulus at the glass ball contacts by performing inter-particle experiments. In order to study the effect of roughness on the impact loading behavior, the surface of several glass balls was fabricated by rubbing them against medium macrogrit sandpaper to increase the roughness.…”

“…The base (blocks) are of 9 × 9 cm square and 6 cm thick. The Poisson's ratio of the blocks was obtained from literature sources based on the material type [32,[38][39][40], while the Young's modulus of brass and glass balls was adopted based on Marinack et al [32] and Sandeep and Senetakis [20]. The density of the blocks was estimated in the laboratory.…”

“…Therefore, the current dynamic impact loading tests can also result in a greater plastic deformation for rough surfaces which leads to reduced COR values. In grain-grain static normal loading experiments for several material combinations (approximate grain size is 2-3 mm), Sandeep and Senetakis [20,51] reported plastic deformation of asperities at a very low magnitude of normal forces (even less than 0.1 N) which mainly depends on material type and surface roughness. They reported a greater magnitude of plastic deformation for rough surfaces.…”

“…However, for a successful application of the Hertz-Mindlin law, researchers need normal and tangential 2 of 14 stiffness as well as the interface friction parameters. Recent experimental studies [18][19][20] obtained the values of inter-particle friction (µ) at the grain-scale for various materials including glass balls (with an average µ ≈ 0.1). The normal stiffness between two bodies can be obtained using quasi-static grain-scale experiments [18,21] or through COR using dynamic impact loading tests [22].…”

Simulations of realistic granular soils in oedometer tests using physics engine

“…There was a large body of literature focusing on rigorous laboratory tests to determine inter-particle friction coefficients of various sands [75][76][77][78][79][80] . Sandeep and Senetakis (2018) 80 performed an excellent review of these studies and found that inter-particle friction coefficients are 0.28 ± 0.08 for crushed limestone, 0.19 ± 0.04 for quartz sands, and 0.12 ± 0.02 for glass beads. Therefore, 0.28 is used as in inter-particle friction coefficient for crushed limestone; 0.19 is used as inter-particle friction coefficient for Agsco sand, Griffin sand, and Ottawa sand; and 0.12 is used as inter-particle friction coefficient for glass beads.…”