- Title
- Elastic and mechanical properties of expanded perlite and perlite/epoxy foams
- Creator
- Allameh Haery, Haleh
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2017
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Syntactic foams are composite materials made by reinforcing a resinous matrix with hollow particles called microspheres. These materials are often used as the core material for sandwich panels, where a combination of low density, high compressive strength, high compressive deformation and high damage tolerance are required, e.g. in the aerospace, automotive and marine industries. Syntactic foams have superior mechanical and thermal properties but they are more expensive and denser than conventionally gas-blown foams. The higher density and cost of syntactic foams is mainly due to the density and cost of the synthetically made microspheres. This problem can be mitigated by using light-weight naturally occurring particles which provide syntactic foams with similar properties but which are significantly cheaper. In this study, the potential of expanded perlite particles (EP particles) in manufacturing light-weight syntactic foams is investigated. Perlite is a glassy volcanic rock of silicic composition and in its expanded form has a high porosity (>95%), low density (~ 0.18 g/cm³) and offers excellent thermal and acoustical insulating properties, chemical inertness, physical resilience, fire resistance and water retention properties. These features, along with the fact that it is abundant and cheap make it a suitable candidate for manufacturing syntactic foams. In this study, the structural, microstructural, physical and mechanical properties of EP particles were investigated. The elastic properties of packed EP particle beds were characterised by the isotropic elastic moduli Poisson’s ratio and Young’s modulus, calculated from elastic wave speeds along the axial (compaction) direction for a wide range of compaction densities. It was observed that during compaction to achieve different densities, some crushing of particles into smaller particles and platy debris occurred. Consequently, analyses were conducted based on both the raw compaction densities and densities modified by the removal of debris from consideration, on the assumption that debris is non-structural. Based on the raw compaction densities, Young’s moduli of the packed EP particles were found to vary in the range 31.4 - 371.3 MPa, while based on the modified densities, they varied in the range 31.4 - 152.8 MPa for the compact densities ranging from 0.1 to 0.375 g/cm³. Poisson’s ratio of packed EP particles did not show a large variation with compact density in the range 0.1 - 375 g/cm³; Poisson’s ratio was about 0.3. The equation for Poisson’s ratio is independent of density, hence the values obtained based on the experimental and modified densities resulted in the same Poisson’s ratios. Four analytical models were applied to predict the elastic moduli of packed beds of EP particles within the porosity range 84 - 95%. Models were assessed on their ability to successfully predict the elastic moduli of these highly porous bodies from the properties of solid perlite for both cases: using the raw compaction density and the modified density. It was found that the Wang (Minimum Solid Area) model was able to estimate Young’s modulus, while the Gibson and Ashby model was reasonable for the average behaviour of both of the elastic moduli. The best agreement, however, was obtained through the Phani model utilising our modified shape factor. The impact of the research was broadened by dispersing EP particles in a matrix of epoxy resin and the manufacture of light-weight EP/epoxy foams. Foams were fabricated with three distinct particle size ranges and, within each size range, the samples covered a density range 0.15 - 0.45 g/cm³. The effects of particle size and foam density variations on the compressive strength, effective elastic modulus and modulus of toughness of the EP/epoxy foams were investigated. The compressive properties of the EP/epoxy foams showed a strong dependence on the foam density, but were almost independent of the particle size. The compressive strength of the EP/epoxy foams was found to vary linearly in the range 0.15 - 1.77 MPa with the foam densities ranging from 0.15 to 0.45 g/cm³. However, the Young’s modulus and modulus of toughness of the EP/epoxy foams varied parabolically in the ranges 33 - 227 MPa and 0.01 - 0.35 MPa, respectively. The elastic properties of the EP/epoxy foams were characterised by adopting an isotropic model for the medium and measuring the elastic wave speeds (i.e. longitudinal and shear wave) in the axial direction (similar to the measurements of the particle beds). Quasi-static compressive test results were compared with those obtained by the elastic wave tests. Both were observed to follow the same qualitative pattern, however the Young’s moduli measured using elastic waves were more than twice those obtained from the mechanical tests. Poisson’s ratio showed an increasing trend, ranging from 0.17 to 0.34 over the foam density range, and appeared to be influenced by the increase in contact surface area between the particles and the matrix as the foam density increased. Post-test scanning electron microscopy (SEM), coupled with photogrammetry during the tests, were used to understand the behaviour of the foams under compressive load. The observations revealed the presence of three different failure modes for all of the foams, regardless of their particle size and density, however the strain to activate each mode was different for each foam type. In addition, the observations showed that the formation of wedge-like fragments in the foam samples under applied compressive stress were due to the effects of pure shear (i.e. the deviatoric components of the applied stress). However, the compressive deformation due to the effect of the hydrostatic components of the applied stress was concentrated in the middle of the foam samples.
- Subject
- elastic properties; mechanical properties; expanded perlite; perlite/epoxy foams
- Identifier
- http://hdl.handle.net/1959.13/1342439
- Identifier
- uon:28964
- Rights
- Copyright 2017 Haleh Allameh Haery
- Language
- eng
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