DEVELOPMENT OF A THEORETICAL MODEL TO PREDICT THE STRESS RUPTURE BEHAVIOUR OF COMPOSITE MATERIALS

Due to their high strength and microstructural stability at elevated temperatures, composite materials are used for turbine blades production, aerospace industries and other several engineering applications. In this work, a theoretical model is developed to describe the stress rupture behaviour of fibre reinforced composite materials. The model predicts the time to rupture for a certain rupture stress and temperature. It is based upon the interaction bet-ween matrix and fibres. Matrix flows under the applied load and an interfacial shear stress is developed at the fibre/matrix interface. This generates a normal stress on the fibre which contributes to the total load bearing capacity of the composite. Fibre fracture occurs when the normal stress reaches the fibre fracture stress. This may lead to the sudden failure of the composite if the matrix fails to sustain the applied load and the broken fibres are shorter than the transfer length. Failure of the composite may be delayed by the ability of the matrix to sustain the applied stress and reload broken fibres having lengths longer than the transfer length. Stress concentration arising from microstructural imperfections may cause premature fibre fracture and reduce the time to rupture. To account for that, a stress concentration factor was introduced in the model. Thermal residual stresses resulting from differential thermal expansion mismatch between fibres andmatrix are also considered.