| Fracture of matrix material caused by a tensile break in a fiber has been investigated. A model was constructed, consisting of two inextensible fibers touching end-to-end and embedded in an elastic block. Energy release rates were calculated by FEA for a circular crack growing outwards from the point where the fiber ends separated as they were pulled apart. The results are compared with experimental observations on steel rod/silicone resin systems. It is found that, when a fiber breaks, a circular crack grows outwards in a stable way under increasing load. After the crack reaches a certain size, approximately half way to the edge of the resin block, the strain energy release reaches a minimum value and then increases, and the crack accelerates. The force required to propagate a crack is predicted successfully by linear elastic fracture mechanics at all stages of crack growth. In particular, good agreement was obtained with the maximum force that the system could support--the breaking load.;Fracture of fiber composites under shear deformation was simulated by applying a tension to the rod in a bush mounting. A bush mounting consists of a cylindrical rubber tube bonded on its inner and outer curved surfaces to a rigid rod and cylindrical tube, respectively. FEA results reveal that tri-axial tension occurs in the matrix at the rod/matrix interface corner although the bonded rubber matrix is mainly in shear deformation. Therefore cavitation is expected to take place at that corner. After a crack is initiated at this interface corner, a constant force is predicted to propagate the interfacial crack.;When the sample was surrounded by a rigid tube, representing neighboring fibers surrounding the broken one, growth of a crack required an increasing load at all stages. The sample finally fractured when the broken fiber was pulled out with resin still attached to it. Many inclined cracks initiated at the rod/matrix interface were observed. This is attributed to shear deformation in the matrix. |
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