Micromechanical Parameters from Macromechanical Measurements on Glass Reinforced Polypropylene

In recent years many elegant techniques have been developed for the quantification of composite micromechanical parameters. Unfortunately most of these techniques have found little enthusiastic support in the industrial product development environment. We have developed an improved method for obtaining the micromechanical parameters, interfacial shear strength, fibre orientation factor, and fibre stress at composite failure using input data from macromechanical tests. In this paper we explore this method through its application to injection moulded glass-fibre-reinforced thermoplastic composites. We have measured the mechanical properties and residual fibre length distributions of glass fibre reinforced polypropylene containing different levels of glass fibre. The level of fibre-matrix interaction in these composites was varied by the addition of maleic anhydride modified polypropylene “coupling agent”. This data was used as input for the model. The trends observed for the resultant micromechanical parameters obtained by this method were in good agreement with values obtained by other methods. Given the wealth of microstructural information obtained from this macroscopic analysis and the low level of resources employed to obtain the data we believe that this method deserves further investigation as a screening tool in composite system development programmes.