Glass mat reinforced thermoplastics - material, process and selected applications

Abstract: The work presented in this thesis covers the processing of glass mat reinforced thermoplastics, GMT, and the mechanical properties of this material group. The thesis evaluates the possibilities of the material group from a processing and mechanical properties point of view. An improved method for measurement of fibre matrix adhesion has been developed. A new test equipment have been developed, which can be used in interfacial shear stress tests of fibre-matrix systems. The effects of the processing parameters time and temperature on the shear strength of a glass fibre-polypropylene (GF/PP) fibre-matrix system have been evaluated with the suggested microtension test. Both processing time and temperature significantly influence the shear strength. The mechanical properties of the glass mat reinforced thermoplastic were studied, and the influence of the processing parameters applied pressure, time and mould temperature were examined. The experimental results were analysed by multiple regression. Inspection of samples revealed artefacts which influenced the conclusions previously drawn, which were based on the statistical results only. A route to combine the regressin model with physical models through reverse Taylor expansion is suggested. The use of vibrational energy in the processing of GMT was studied. Vibrational energy improved the quality of the GMT material both by improving the mechanical properties and by decreasing the coefficient of variation of the measurements. The use of sequential pressing was studied, and shown to improve the mechanical properties. Energy absorption during the fracture of GMT has been studied. The force required to slit a specific material reaches a steady-state value which depends only on the geometry of the cutting edge and the material dimensions. It was found that theories developed for metal cutting can be applied.The force-displacement curve of the slitting process exhibits a certain amount of scatter. A small scatter equals homogenous fibre distribution and well bonded fibres, while a large scatter equals poor bonding and poor fibre distribution.The sound-absorbing characteristics and the mechanical properties of expanded GMT are other aspects of thermoplastic composite material that have been studied. The thermoplastic composite materials can be efficiently recycled. Chips from a trimming operation and material from rejected parts that had been subjected to granulation were fed into an injection moulding machine and parts were produced. The GMT material produced in this way had properties at least equal to virgin polypropylene in all properties but impact strength. Three new applications based on GMT are presented in the study. The applications are: Sound-absorbing and load-bearing structure, an interior energy management system and a foot prosthesis.