A new method of evaluating the interfacial properties of composites by means of the gradual multi-fiber fragmentation test

A new method for evaluating the interfacial properties of fibrous composites based on a fragmentation technique has been proposed by use of the gradual multi-fiber composite, in which the inter-fiber spacing is gradually changed. The results showed that as the inter-fiber distance increased, the aspect ratio of broken fibers decreased while the fibre/matrix interfacial shear strength increased. When the reciprocal of the inter-fiber distance was taken for the above relationships, both the aspect ratio and interfacial shear strength were found to show a saturated value. This means that the gradual multi-fiber composite indicates an upper bound in aspect ratio and a lower bound in interfacial shear strength, while the single-fiber composite shows a lower bound in aspect ratio and an upper bound in interfacial shear strength. It was concluded that this fragmentation test could be a new method for composite evaluation, since reducing the difference between these two bounds is effective for composite strengthening. In addition an elasto-plastic finite-element analysis was carried out to relate the above results with the fiber stress distribution around fiber breaks. It is proved that the bound obtained in the gradual multi-fiber composite test is closely concerned with stress concentrations caused by a group of multi-fiber breaks.