The present work has successfully used an ingenious experimental technique to make a detailed examination of flow fields and fibre orientation patterns in a number of geometries. The experimental technique consisted of dispersing short glass fibres in mixtures of epoxy resins with matching refractive indices to that of the glass fibre. This made the glass fibres to 'disappear' in the mixtures and resulted in transparent mixtures. Light-reflective nickel particles and opaque tracer fibres were added to the mixture in order to investigate velocity fields and fibre orientation patterns. Experiments have covered concentrated, semi-concentrated, and (almost) dilute regimes. It has demonstrated a number of phenomena in flow-induced fibre orientation particularly in the concentrated region which have not been described before, and which should be taken into account in any predictive theories of fibre suspension flow and orientation. In the highly-concentrated suspensions, where C > (d/21), plug-flow type velocity fields exist. (Here C is the mixture concentration, d is the fibre diameter, and 21 is the fibre length). The fibre resin mixtures behave as non-homogeneous continua where fibre clumps are separated by resin-rich areas. These clumps apparently deform under shear, but seem capable of elastic recovery, facilitated by shear-induced clump rotation. In the semi-concentrated regime, where (d/21)<SUP>2 < </SUP> C < (d/21), expected degrees of alignment are diminished by fibre-fibre interactions. In this concentration regime and in some flow situations there is some evidence of rate dependence of alignments achieved, i.e. dependence on viscous stress levels. In the (almost) dilute regime, where C is just higher than (d/21)<SUP>2</SUP>, the fibre behaviour is in theory predictable from single fibre mechanics if the flow fields are of the linear type. However, in practice this is seldom the case. For this reason a theory has been developed and implemented in a computer program, which predicts fibre motion in arbitrary velocity fields.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:637979 |
| Date | January 1991 |
| Creators | Mahmoudzadeh, H. |
| Publisher | Swansea University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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