Effects of Interfacial Conditions on Critical Aspect Ratio of Fibres in Single-Fibre Composites

Abstract

Single tungusten fibre-copper matrix composites containing continuous initially brittle fibres were prepared by a plating method. Interfacial conditions between fibre and matrix were varied by coating carbon, boronnitride and nickel on fibres before plating. Tensile tests were made at room temperature and the critical aspect ratio was measured from the load-elongation curves. Effects of interfacial conditions on the deformation and fracture behaviour and the load transfer mechanism were discussed. The results obtained are as follows.(1) When Vf is smaller than Vmin, the initially continuous fibres in the composites fracture continually into shorter lengths and finally reach lc⁄2. The critical aspect ratio and the shear stress at the interface obtained according to the Kelly model were found to depend upon Vf and the interfacial conditions.(2) The external load was found to be transfered from the matrix to the fibre even when the interfacial bonding is almost zero. This result was explained in terms of the frictional shear stress arising from compressive stresses caused by the differences in contractions and deformation amounts between the fibre and the matrix.