Multi-Scale Assessment of the Role of the Particle Shape on the Crushability of Sand

Seo, Dawa

doi:https://doi.org/10.21985/n2-b6q8-m410

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Multi-Scale Assessment of the Role of the Particle Shape on the Crushability of Sand

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Granular materials consisting of discrete particles, are a pervasive material in nature and play a major role in disparate fields of science and technology. To control and manipulate the granular materials in engineering, enriching our understanding of their fundamental characteristics and mechanical behavior is crucial. In this context, one of the major challenges concerning particulate materials composed of fragile particles is their response at high pressure. The extreme conditions cause the evolution of size and shape of their grains, a phenomenon referred to as breakage. The evolving particle-scale attributes induce the critical change in rearrangement of microstructures leading to macroscopic deteriorations, affecting the safety and serviceability of the granular system. Therefore, it is essential to comprehend the effect of size reduction and shape alterations in crushable granular materials at the multi-scale mechanics. The goal of this study is therefore to enhance our understanding of crushable granular materials mechanics, especially in light of the effect of particle shape and the evolution of shape attributes under continuous breakage. In this thesis, first, high-pressure compression tests with concurrent 3D X-ray tomography were conducted at assembly scale with two different morphological types of sand. The attained digital images during the experiments were used in conjunction with a tracking algorithm able to quantify the consecutive response of sand grains. The tracking algorithm, for example, allowed the isolation of the individual breakage events and the quantification of number and geometry of the fragments resulting from each grain rupture in the packed sand experiencing collective comminution. Furthermore, the shape-dependent breakage models at grain scale were proposed to predict the failure strength of crushable grains with particle-scale attributes, size, and shape. The performance of the proposed models was assessed with the measured particle failure strength through the diametral compression test which was conducted on single particles of varying size and shape. Moreover, a level-set discrete element method was used to replicate the oedometric compression test to investigate the evolving response of stress distribution in the assembly of a crushable granular system. With the benefit of computational modeling, the role of geometric modelling in a discrete element method was examined to evaluate the optimal level of particle geometry representation. Furthermore, the virtual laboratory experiments were examined to validate the possibility of attaining ultimate size and shape attractors. The conclusion summarizes the main findings of the thesis and discusses the possible direction of applicable contribution of this thesis and future research.

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