A 3D finite element model has been developed to identify the main causes of variability in the microdroplet test, which is commonly used to characterise the interfacial shear strength between polymer matrices and single filaments. A more realistic droplet shape and test configuration, including meniscus details and prismatic shear blades, have been modelled for a carbon fibre/epoxy system to simulate a more representative set up than is commonly used in the literature. The interfacial behaviour has been modelled using a cohesive surface contact and fibre breakage has been captured using a maximum stress criterion. A statistical study has been performed to systematically evaluate the influence of key geometrical test parameters on the variability in the measured interfacial shear strength values and the likelihood of fibre breakage. Parameters studied are fibre embedded length, fibre diameter, shear blade radial opening distance and shear blade axial misalignment.
Results of the studied carbon fibre /epoxy system suggest that fibre embedded length and the combined effects of the shear blade radial distance and the shear blade axial misalignment are the most significant sources of variability for the measured interfacial shear strength. However, fibre embedded length and the shear blade radial distance are the most significant variables contributing to fibre breakage.
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