Investigation into stress transfer characteristics in alumina-fibre/epoxy model composites through the use of fluorescence spectroscopy

In composite materials, fibre/fibre interaction phenomena due to fibre fail ure are crucial in determining the composite fracture behaviour. Indeed, th e redistribution of stress from a failed fibre to its intact neighbours, an d stress concentration induced in the neighbouring fibres, determine the ex tent to which a break in one fibre will cause more breaks in others. In thi s paper, we have used fluorescence spectroscopy to study the stress transfe r and redistribution induced by fibre fracture in two-dimensional Nextel-61 0 fibres/epoxy-resin micro-composites. The stress along the fibres was mapp ed at different load levels, and specimens with different inter-fibre dista nce were used to study the fibre content effect. The interfacial shear stre ss distribution along broken and intact fibres was derived by means of a ba lance of shear-to-axial forces argument. The experimental stress concentrat ion factors (SCF) were smaller than values predicted from our model based o n the cell assembly approach. As expected the 2D configuration allows acces s to the upper bound of the SCF in real composites. For the several specime ns tested, a region of matrix yielding was observed behind the fibre fractu re and no-debonding at the interface was detected. The measured SCF values agree well with those reported in recent study for carbon-fibre/epoxy model composites. (C) 1999 Kluwer Academic Publishers.