An Analysis of Microdroplet Test: Effects of Specimen Geometry, Matrix Type, Fibre Treatment and Water Ageing

Abstract

The microdroplet test has been used to characterize the interfacial bond in fibrous composite materials. The specimen consists of a length of fibre with a drop of resin cured on it and pulled out while the drop is being supported by a platinum disc with a hole. A properly tested specimen fails at the droplet's tip-fibre interface, revealing the ultimate interfacial shear strength. The microdroplet test is carried out under optimal testing conditions, established from our previous work, in order to obtain fully debonded specimens for the interfacial shear stress analysis of the fibre-matrix bond. Three thermosetting resins are applied on silane coated and acetone washed (silane removed) glass fibres in order to investigate the influence of the silane coupling agent on the fibre-matrix bond. Also, these systems were aged in water at room temperature for periods of 3, 6 and 10 weeks and the influence of water degradation on the fibre-matrix bond is investigated for both groups of glass fibres (silane coated and acetone washed). The group of glass fibres washed in acetone produced weaker fibre-matrix bond and accelerated water degradation of the interfacial bond. It is found that the influences of two dominant geometric parameters (conus angle and droplet length) on the test results are reciprocally opposite, generating scatter in the experimental results. It is shown in this work that the microdroplet test can be used as a reliable tool for measurement of the fibre-matrix adhesion.