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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 (O-GFA) 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. Za opredelitev pretočnosti granuliranih materialov izpostavljenih enoosni tlačni obremenitvi lahko uporabimo GFA indeks. GFA indeks se določi kot integral porazdelitve notranjega tlaka vzdolž stene cilindra GFA naprave. Notranji tlak pa je posledica enoosne tlačne obremenitve, ki deluje na granulirani material v cilindru naprave. V nalogi je predstavljen optični analizator trenja granuliranih materialov (O-GFA). Naprava za določitev deformacij testnega valja uporabljenih za izračun porazdelitve notranjega tlaka uporablja metode korelacije digitalnih slik (DIC). Za validacijo razvite O-GFA naprave so bili uporabljeni trije vzorci granul SS316L jekla z različnimi srednjimi velikosti delcev. Z rezultati je bilo potrjeno, da srednja velikost delcev uravnava notranje trenje granuliranih materialov. Nadalje je v nalogi raziskan vpliv širine porazdelitve delcev (PSD) na GFA indeks in s tem povezano pretočnostjo materialov. Pokazano je bilo, da se s povečanjem širine PSD GFA indeks poveča, notranje trenje se zmanjša in razmerje notranjega tlaka ostane nespremenjeno. Pokazano je bilo tudi, da je GFA indeks neodvisen od obremenitve. Glavna prednost uporabe DIC metode pri O-GFA napravi je da omogoča določitev kontaktne točke med batom in materialom. Prav tako, pa se je mogoče izogniti območju meritev, kjer je prisoten robni efekt. Z uporabo O-GFA je bila doseženo 2% izboljšanje natančnosti GFA indeksa. Parametrična analiza napake je pokazala, da največji doprinos k skupni napaki (7.5%) izhaja iz DIC meritev deformacij vzdolž merilnega valja. Pokazana je tudi bila robustnost metode glede na število merilnih točk potrebnih za določitev deformacij in notranjega tlaka. Ugotovljeno je tudi bilo, da je določitev GFA indeksa in pretočnosti granuliranih materialov izpostavljenih enoosni tlačni obremenitvi z O-GFA napravo alternativa tradicionalnim metodam, kjer je za določitev lastnosti potrebno izvesti dva ločena eksperimenta. |
