Analysis of interfacial micromechanics in microdroplet model composites using synchrotron microfocus X-ray diffraction

Microfocus X-ray diffraction, a synchrotron radiation based technique, has been used to determine the fibre/matrix interfacial shear stress within a new type of model composite. This model composite comprises a single fibre of poly(p-phenylene terephthalamide) or poly(p-phenylene benzobisoxazole) with an epoxy resin microdroplet attached along its length. Shifts of meridional Bragg peaks as a function of stress have been determined for each fibre type and used as a calibration of fibre stress both inside and outside of the droplets. The variation of stress was mapped along the fibre in the microdroplet composites at different levels of applied stress. A modified single fibre pull-out shear lag analysis with an interfacial failure criterion was used to interpret the data. The microdroplet geometry, which is similar to the more established microbond test has several advantages; the primary advantage is that there is no need for a mechanical restraint on the droplet, as in a microbond test.