The fibre reinforcement of low density rigid polyurethane foam

Pigg, William (1986) The fibre reinforcement of low density rigid polyurethane foam. Doctoral thesis (PhD), Manchester Polytechnic.

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Abstract

The mechanical and fracture behaviour of low density rigid polyurethane foams have been examined. Tensile, yield and compressive strengths, fracture parameters, flexural and tensile rigidities and Poisson's ratio have been measured for non-reinforced and reinforced foams of various densities. Glass fibres and polyester fibres were used seperately for reinforcement and together as hybrid reinforcement. The fracture behaviour has been analysed by means of linear elastic fracture mechanics. An analysis of the effects of the cellular nature of the foams has been proposed and the behaviour characterised in terms of plane strain fracture toughness, Kic and the strain energy release rate, Gic particular attention being paid to the reporte9 discontinuity in the latter parameter at densities around 100 - 140 Kgm-3. Throughout the fracture analysis, results have been carefully explained in terms of the plane strain conditions and the state of the plastic zone ahead of the crack tip. The deformation and fracture characteristics of the foams have been considered in terms of morphology, the nature of any reinforcement (deformable or non deformable) and the strength of the fibre matrix interfaces. In the case of polyester fibre, attempts have been made to enhance fibre matrix compatability by the use of titanate based coupling agents and a comparison has been made between the reinforcement behaviour of undrawn and commercially drawn polyesters in terms of fibre pullout / fibre breakage mechanisms.