This paper presents a custom-built micromechanical testing apparatus to analyze the interface shear behavior of geomaterial contacts. This apparatus allows for the investigation of rolling and sliding friction of a wide range of geomaterial contacts under various testing parameters, including normal load, displacement rate, and dry and wet conditions. The device is instrumented with sensors (load, displacement, and camera) and a computerized data acquisition system to measure and record the force, displacement, and images of the contacts during the test for in-depth study. The images are captured from the bottom of the sliding platform while shearing for only the contacts made of particle and transparent continuum materials. The shear response accuracy for the geomaterial contacts tested in the custom-built micromechanical apparatus is demonstrated by comparing the results of the same contacts obtained from a high-end tribometer apparatus. It was found that test findings from a custom-built apparatus are as accurate as those from a high-end tribometer and reliable for the micromechanical analysis of geomaterial interactions. Further, experiments were performed on different types of interface contacts and under different conditions to demonstrate the apparatus’s sensitivity. These findings indicate that the apparatus stiffness is sufficient and facilitates the understanding of micromechanical behavior and estimates basic yet essential inputs required to comprehend the complex behavior of geomaterials.
The study of effects of particle breakage on the mechanical properties of soil composed of porous particles is challenging due to the heterogeneity of the shape and inner void structure of individual particles, even for an identical soil sample, which imparts a compound effect on the mechanical properties. Advancements in three-dimensional (3D) printing technique have enabled the replication of objects with the same shape but different inner structures. This study investigated the feasibility of replicating porous and non-porous particles with the same particle shape characteristics, such as form, waviness, and texture, using 3D printing technique. The particle shape characteristics were evaluated using image analysis. Single particle crushing and triaxial compression tests were conducted to characterize the mechanical properties of the 3D printed and porous volcanic soil particles. It is observed that the mechanical response in the single particle crushing test varies for volcanic soil, which may be attributed to the heterogeneity in the shape and porosity of the particles. However, for each type of 3D printed particle, the response has a high repeatability and varies based on particle porosity. Furthermore, the effects of porosity on the shear response are demonstrated through triaxial tests on 3D printed particles of different porosities. It is noted that although a quantitative comparison is not possible, a qualitative similarity is observed in the response of the 3D printed porous particles with natural porous volcanic soil. Thus, insights into the mechanical response of porous particles can be gained using 3D printed particles.
The paper presents new insights into the particle kinematics and tribological aspects and their effects on the non-dilative interface shear response from novel experimental investigations. A custom-designed apparatus that enables image analysis of particulate-continuum materials interactions from the bottom of the interface plane while shearing was developed. The effect of influential factors on the frictional mechanism, particle kinematics, and subsequently on the friction coefficient was investigated by performing experiments on three types of sands at different normal stresses with a transparent acrylic sheet and smooth geomembrane. The results demonstrated that the frictional response of the acrylic sheet and geomembrane was comparable, indicating that their particle kinematics at the interface could be similar. However, the critical normal and peak shear stresses differed due to the materials' hardness. The image and micro-topographical analysis of the tested interfaces revealed that the box fixity, particle shape, and normal stress influence particle kinematics and shear-induced surface changes. The fixed box has shown restricted particle movements compared to the conventional box. Angular and smooth spherical particles exhibited lesser kinematics despite a huge difference in the shape and shear-induced surface changes. Rough spherical particles have larger displacements and shear-induced surface changes than smooth spherical particles.
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