Abstract
Microstructure and fracture mechanical behaviour of injection-moulded, longer glass fibre-reinforced polypropylene (Verton; aspect ratio approx 320) were studied as a function of fibre volume fraction and compared to that of shorter fibre-filled polypropylene (aspect ratio approx 70). Toughness was measured using instrumented notched Izod, falling weight impact tests, and compact tension specimens. It was found that the addition of longer fibres generally increased the toughness of the material, although more significant increases were seen in the impact tests than were seen in the compact tension test. For the latter results, a correlation between toughness improvement and microstructural details was performed on the basis of the microstructural efficiency concept, a semi-empirical approach of the form K sub c,C = (a* + nR)K sub c,M , where, K sub c,C and K sub c,M are the fracture toughnesses of the composite and the matrix, respectively, a* is a matrix stress correction factor, n is a scaling parameter and R is a fibre reinforcement effectiveness factor. The latter corrects for differences in the composite microstructures, and incorporates effective fibre orientation factors, layering of injection moulded parts, and fibre volumes in the different layers. Graphs, Photomicrographs. 19 ref.--AA