Mechanical properties and structure of extruded short glass fibre-filled polyethylene

The work described in this thesis concerns the mechanical properties and structure of extruded short glass Fibre-Filled polyethylene. High density polyethylene was compounded with E-glass and coupling agent, and extruded into 110 m diameter pipe, using a normal production extruder, by Stewarts & Lloyds Plastics, Huntington. A normal die and a novel die, based on the Monsanto expanding mandrel die, were used to produce pipes with varying fibre orientation distributions (FED).

The structure of the pipe was analysed in terms of density, crystallinity, glass weight Fraction, and Fibre length and orientation distributions. Various mechanical properties were measured, to confirm the structure results, namely tensile creep and compression modulus, and tensile strength.

3-point bending tests of pipe were undertaken. The measured deflections under load were compared with simple bending theory and finite element analysis predictions. Kc, a Jc,-testing of samples was undertaken. JC-testing was not successful, so Kc testing was adopted.

The Kc results are analysed in terms of FOD and test seed, and it is shown that alignment in the direction of load does not allays produce the most resistance to crack growth. Fatigue testing of impact tension and slant-edge cracked specimens was undertaken, with crack growth at several angles to extrusion. Results are very different for samples produced with the different dies, and also depend on fibre length, glass volume fraction, angle to extrusion, and test stress amplitude.