The single-fibre pull-out method: its advantages, interpretation and experimental realization

Past results from the single-fibre pull-out tests are reviewed and new results obtained with carbon in thermoplastics are presented. The force-distance curve during pull-out indicates some pseudo-ductility, in some cases, as the applied force builds up to the failure load. However, the failure itself is not ductile; rather, it is sudden, suggesting brittle fracture. The debonding force vs. embedded length (L) plots range from straight lines intersecting the origin, through smooth curves, to scatter diagrams, depending on the fibre and polymer. Interfacial shear strengths estimated from the shorter embedded lengths are often high and, quite frequently, higher than that of the polymer matrix. In addition, there is normally no correlation between interface properties (strength or work of fracture) and the corresponding polymer properties. This could well be due to the growth of an oriented interphasial layer, with a modulus and strength up to six times greater than that of the bulk polymer, as has been observed for modulus at least, with particulate reinforced materials.