MICROSTRUCTURE AND FRACTURE-BEHAVIOR OF SHORT AND LONG FIBER-REINFORCED POLYPROPYLENE COMPOSITES

Microstructure and fracture mechanical behaviour of injection-moulded, longer glass fibrereinforced polypropylene (Verton* aspect ratio ≈ 320) were studied as a function of fibre volume fraction and compared to that of shorter fibre-filled polypropylene (aspect ratio ≈ 70). Toughness was measured using instrumented notched lzod and falling weight impact tests, as well as 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 Kc,C = (a* +nR)Kc,M, where, Kc,C and Kc,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. © 1990 Chapman and Hall Ltd.