Factors which influence the reliability of the assessment of interfacial bonding in fibrous composites using the pull-out test

Recent developments in the single fibre pull-out technique has made it possible to determine the interfacial shear strength τi (IFSS), the toughness of the interface Gi and the matrix shrinkage pressure on the fibre Po utilizing this test. In contrast, other techniques only allow the determination of the IFSS. However, scatter in the values of the IFSS and the other interfacial parameters has been reported by different researchers working on a given fibre–matrix composite system using this technique. This brings into question the reliability of results from such analyses. Careful examination indicates that such scatter can probably be attributed to factors such as the testing configuration and specimen geometry which were previously ignored. The governing equations for analysis of experimental data have been shown to depend on the loading configuration. It will also be demonstrated that different fibre–matrix systems require modified assessment methodology since the range of experimental pull-out data which can be gathered would differ. This is due to the fact that the maximum embedded length specimen which can be pulled-out successfully during testing is dependent on the physical properties of the fibre and matrix, and the interfacial bond strength. Analysis methodology developed based on a recognition of these factors allows reliable assessment of interfacial bonding in fibrous composites.