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

The deformation micromechanics of singlefibre embedded model composites of poly(p-phenylene benzobisoxazole) (PBO) and poly(p-phenylene terephthalamide) (PPTA) fibres, embedded in an epoxy resin have been examined using synchrotron microfocus X-ray diffraction. Single fibres (in air) were deformed and the c-spacing monitored to establish a calibration of crystal strain against applied stress. Subsequently, the variation in crystal strain along fibres, embedded in the resin matrix was mapped using synchrotron microfocus X-ray diffraction. Raman spectroscopy was then used to map molecular deformation on the same samples (recorded as shifts in the Raman band wavenumber) in order to provide a complementary stress data. A shear-lag analysis was conducted on the axial fibre stress data in order to calculate interfacial shear stress and identify different stress-transfer modes at fibre/resin interfaces. The results establish that the axial fibre stress distributions measured by synchrotron microfocus X-ray diffraction correlate well with those obtained using Raman spectroscopy. The interfacial shear stress data derived from the stress-transfer profiles also show a good degree of correlation.