The stiffening in tension of injection-moulded polypropylene with the addition of glass fibres or spheres was found to depend on strain, time and the direction relative to that of the melt flow, as well as on the percentage and aspect ratio of the glass inclusions. Under loading of long duration this stiffening, expressed in terms of the stiffness factor, increased with time for fibre-filled material but varied little for the sphere-filled. In the latter case, the tensile creep could be predicted with some accuracy by a simple model. The anisotropy of the fibre-filled polypropylene was not time-dependent and conformed to the theory of orthotropic materials.
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Weidmann, G.W., Ogorkiewicz, R.M. Time-dependence of the tensile stiffness and anisotropy of a reinforced thermoplastic. J Mater Sci 9, 193–200 (1974). https://doi.org/10.1007/BF00550941
- Aspect Ratio
- Simple Model