Photoelastic characterisation of interfacial stress distribution of a single short-fibre model composite under tensile loading

The shear stresses at the interface between a polyester fibre and an epoxy matrix in a short single-fibre model composite specimen were measured using photoelasticity. A dark-field circular polariscope was employed to monitor the stress field in the matrix during tensile loading. With this method, the stress level of a Nth isochromatic fringe in the matrix intersecting the fibre can be obtained. The model composite specimen was loaded in uniaxial tension and the isochromatic patters along the fibre-matrix interface were recorded for several increments of load. In the experiment, it was observed that the number of fringes increased with the applied load, which indicated an increase in the stress transfer from the matrix to the fibre. Debonded zones were also identified where the shear stresses were at a minimum. The shear stress vs distance along the fibre plot showed that monitoring isochromatic fringe patterns can accurately measure the stress transfer and stress distribution at the interface in the thermoplastic-thermosetting system presented in this work