Evaluation of particle size distribution influence on flowability of granular materials using a digital image correlation method : doctoral thesis

english

doktorska dela

2021

digital image correlation   flowability   granular materials   internal friction   particle size distribution   uniaxial compression

Univerza v Ljubljani, Fakulteta za strojništvo
(Obvezni izvod spletne publikacije)

With the aim to characterize the flowability of granular materials under uniaxial compression force a GFA index can be used. The GFA index is calculated based on the integration of the internal pressure distribution along the cylinder wall caused by uniaxial compressed granular material contained in the cylinder. In this thesis an optical granular friction analyzer (OGFA) is presented, where a digital image correlation (DIC) method is utilized to assess the cylinder strains used to calculate the internal pressure distribution. For the purpose of demonstration and validation of the developed O-GFA apparatus, three SS316L granular material samples with different particle mean sizes were tested and the results confirm that the particle mean size regulates the internal friction of granular materials. Further, the study of the influence of particle size distribution (PSD) width on GFA index and its related flowability showed that as PSD width increases, the GFA index increases, internal friction decreases and the internal pressure ratio remains constant. It has also been shown that the value of GFA index is load independent. Based on the experiments performed and presented results the main advantage of using the DIC method based O-GFA is that the piston–powder contact point and the region of the integration avoiding the region under the edge effects can be defined. Additionally, a 2% improvement of the GFA index’s accuracy has been achieved and showed by parametric analysis that the most of the observed total error (7.5%) arises from the DIC method-based measurements of the strains along the piston. Its robustness with respect to the number of points considered in evaluation of strains and related internal pressure has been demonstrated. It can also be concluded that, determining the GFA index using the O-GFA for characterizing the flowability of uniaxially compressed granular material is an alternative to traditional methods, which require the individual properties of granular materials i.e. internal friction and internal pressure ratio to be determined through two separate tests.

15.05.2023