- Title
- Fundamental mechanical behaviour of perlite composite foam and applications
- Creator
- Arifuzzaman, Md
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2017
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- The fundamental mechanical behaviour of perlite composite foam is studied theoretically and experimentally for basic understanding and the development of predictive models and practical applications. The existence of plane stress/strain compressive properties and volume fractions of structural elements of perlite foam are conceptualised for the basic understanding, leading to the development of predictive models of compressive properties, and development of sandwich composites for practical applications. Novel composites made of expanded perlite particles and sodium silicate solution were developed. For the composites development, expanded perlite particles were characterised for various densities and porosities. Sodium silicate (as a binder) dehydration behaviour was characterised with phases formed during dehydration i.e. liquid, gel, and solid phases. The water-loss time curve for dehydration was found to have three distinctive parts—a linear part at an early stage for the liquid phase, followed by non-linear part during a period between the commencement of the gel and hydrated solid phase formations, and then another linear part for the hydrated solid phase. For the purpose of sandwich composite development, mechanical properties of Brown paper were investigated by coating the paper on one side with varying sodium silicate content in dilution. When Brown paper was coated with diluted or undiluted binder, its tensile properties were affected due to the sodium silicate content in dilution. The best performance of Brown paper was found when coated with undiluted binder. A novel mechanical behaviour of perlite/sodium silicate composites was studied with the benefits of a new manufacturing method based on perlite particle buoyancy. The objective was to develop perlite composites and to understand the quantitative relations between manufacturing parameters, volume fractions of constituents, and properties. Foams as composites were manufactured with diluted sodium silicate binder for a density range of 0.2–0.5 g/cm³. One of practical milestones achieved for composite properties without reinforcement was a density of 0.3 g/cm³ at a compressive strength of 1 MPa. Manufactured perlite/sodium silicate composites were analysed and discussed for understanding from three different perspectives: manufacturing parameters (binder content, compaction pressure, and compaction ratio), properties (particle size, density, compressive strength, and modulus), and volume fractions of constituents. A rule of mixtures applicable for perlite composites for a constant compaction ratio was developed in comparison with that for particulate composites with non-compaction. This may be a basis for further development for variable compaction ratio. The mechanism of internal structure formation of perlite composite foams due to compaction was identified. Foam and particle envelope densities and volume fractions were theoretically modelled for prediction and practical evaluation. The volume fractions, as functions of manufacturing variables, include those affected by topological change of internal structure of foam after the compaction process, consisting of binder, perlite material, the porous zone of original particles, debris zone, and inter-particle voids. Predictions were validated against directly measured values for foam and particle envelope densities. A problem with the conventional method for obtaining volume fraction of binder was analytically addressed in terms of error sensitivity. Values for volume fraction of binder obtained from the conventional method were found to have errors up to about 300% (or about three times validated errors). An example is given to show how the predictive models can be used for optimisation of manufacturing and properties. The applicability of formulas based on the new evaluative method is also shown for syntactic foams. Experimental results were obtained from a foam density range of 0.16–0.50 g/cm³ and a porosity range of 0.79–0.93 for expanded perlite particle sizes of between 3–4 mm, a compaction ratio range of 1.00–3.56, and a pure sodium silicate content range of 0.05–0.35 g/ml in dilution of water for binder. A predictive model for compressive strength based on the rule of mixtures was developed. A ternary system diagram for binder, debris, and porous particles was conceptualised as the basis for the modelling. Relationships between volume fractions of foam structural elements and binder, and manufacturing variables—binder content and compaction ratio—were quantified. The model prediction capability has been verified as follows: (a) predictions of compressive strength for varying compaction ratio with a constant binder content were made, and differences between prediction and experiment were found to be in a range of –13%–6%; and (b) predictions of compressive strength for varying binder content with a constant compaction ratio were made, and differences between prediction and experiment were found to be in a range of –5.2%–10%. The accuracy of the model predictions may be regarded as being acceptable for understanding compressive strength of perlite composite foam and for practical applications. Novel compressive behaviour of perlite/sodium silicate composite foam was studied in relation to plane stress and plane strain conditions. Plane stress and plane strain conditions were theoretically conceptualised for compressive strength and modulus of perlite syntactic foams, and their existence as experimentally verified for practical characterisation. The highest compressive strength under plain strain and compressive modulus under plane stress were experimentally found to be about 50% and 200% higher than the lowest values under plane stress and plane strain, respectively. A new failure mode under plane strain was identified as the progressive densification. Flexural behaviour of perlite/sodium silicate composites was studied using a new manufacturing method based on flotation of lightweight particles for applications of sandwich foam core materials. The sodium silicate content in composites (a perlite particle size of 2–3 mm) was varied for a range of 0.1–0.3 g/ml, and compaction ratio for moulding for a range of 2.0–3.0. Cracking during three-point bending tests was initiated from the tension sides of specimens. Incidentally, no indentation damage was visually detected on the top surface underneath the loading point. This identification of failure cause may be useful for future improvement of mechanical performance. Under flexural loading, energy absorption in composites was found to be in operation after initial cracking, supporting their candidacy for wide applications where gypsum boards are dominant. It was deduced from both flexural testing results and fracture mechanism that compressive strength is higher than tensile strength, suggesting future directions of mechanical performance improvement. Finally, a sandwich structure consisting of perlite composite foam as core and Brown paper as skin was developed, and its flexural behaviour was studied in relation to properties of constituents and manufacturing variables (binder content and compaction ratio) of perlite composite foam core consolidated with sodium silicate binder by compaction. The sandwich structure was fabricated with the best-performed Brown paper and perlite composite foam core, made by varying binder content and compaction ratio. It was found that the performance of the sandwich structure for core shear strength, skin normal strength, and stiffness was significantly affected by manufacturing variables of perlite foam core. The load carrying capacity of perlite foam core reinforced with Brown paper for the sandwich structure was increased between 3–7 times an unreinforced core, depending on how binder content and compaction ratio were combined for manufacturing the perlite foam core. The flexural failure of perlite composite foam core was initiated from the tension side of the flexural specimen regardless of manufacturing variables. However, when the foam core was reinforced with Brown paper, the failure initiation site shifted to the mid-plane of flexural specimens when binder content and compaction ratio were lowered.
- Subject
- expanded perlite; perlite composite; density prediction; compressive strength prediction; plane stress/strain; flexural properties; sandwich composites
- Identifier
- http://hdl.handle.net/1959.13/1336136
- Identifier
- uon:27557
- Rights
- Copyright 2017 Md Arifuzzaman
- Language
- eng
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