Confined Uniaxial Compaction Observing Triaxial Response of Granular Media under Quasi-static Loading Conditions

• Author / Creator

  Nicewicz, Piotr

• Experimental studies have been carried out in this thesis to enhance the understanding of granular material failure by observing the effects of particle size on material properties. Understanding the granular behaviour of materials is important in pharmaceutical research, product quality in the additive manufacturing industry, and ballistic performance in defence applications. In order to investigate these granular material behaviours in this thesis, two different experimental apparatuses were designed to conduct confined uniaxial compression tests under quasi-static loading conditions. The triaxial compaction response was monitored using a displacement traducer and load cells to derive material property characteristics.

  First, the material response of granular stainless steel 316 was captured using the thick-walled cylinder approach where a load washer and strain gauges  relate: the hydro-static pressure effects as a function of porosity, particle size dependency on wall friction effects, and particle size-dependent failure mechanisms. The average particle sizes investigated were: 127 +-34 um, 309+-88 um,  487+-98 um. Observations revealed that the path of crushing out porosity varied based on the particle size and the frictional effects. Scanning Electron Microscope images were taken to examine the surface features and failure mechanisms of the compacted material. The analysis indicated that smaller particles exhibited significant plastic deformation and flow, while the larger appeared to show micro-cracking which lead to inelastic deformation and particle fracture.
  
  Second, quasi-static uniaxial confined compaction of granular alumina and boron carbide was also studied, observing the triaxial stress effects of the materials as a function of particle size, using the instrumented die approach. The average particle sizes for alumina powder used in the experiments were: 133+-38um,  201+-42um, 290+-52, and 414+-57 um. The material response was captured using load cells and a displacement transducer to relate the hydro-static pressure as a function of porosity, the bulk modulus as a function of hydro-static pressure, and the transmission ratio as a function of applied load all for increasing particle sizes. Investigation of these ceramics revealed that for alumina, increasing the particle size resulted in an increase in strength for a fixed porosity, the bulk modulus did not show clear particle-size dependent trends, and the transmission ratio showed increasing behaviour where larger particles transmitted more load. To contrast, similar particle sizes were investigated for granular boron carbide: 152+-26um, 171+-23um, 303+-46um, and 461+-44 um. For granular boron carbide, the path of crushing out porosity decreased with increasing particle size, the change in bulk modulus of the material increased with increasing particle size, and no clear particle-size dependent trends were observed when looking at the transmission ratio during the compaction. Likewise, for both ceramics, SEM images were taken to observe the surface features of the loose and compacted material to track any failure mechanisms before and after experiments. Post-experiment SEM analysis revealed that alumina powder fragmented from elongated shapes to block-like structures, while the boron carbide powder appeared more circular before the experiments and fragmented into smaller comminuted pieces during experimentation. The degree of fragmentation was strongly correlated with the maximum hydro-static pressure reached during experimentation, regardless of initial particle size.
  
  Altogether, these results are important to better understand the particle-size dependent behaviours in metals and advanced ceramics so that failure regimes can be more accurately conveyed in validating failure models and improving the use of materials in blast mitigating structures.
  

• Subjects / Keywords

  • Boron carbide
  • Ceramics
  • Alumina
  • Mechanics
  • Granular

• Graduation date

  Fall 2019

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-cwr0-8s22

• License

  Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.