The toughness of a brittle material can be drastically increased by the incorporation of aligned fibres. The stress-strain behaviour of their unidirectional fibre toughened brittle matrix composites is not only of fundamental interest but also of technical importance. Thr proposed model gives a complete description of the stress-strain behaviour during tensile resting of a unidirectional fibre toughened brittle matrix composite using parameters describing the microstructure, the micromechanical behaviour, the damage development and the residual stress stare as input. The model reproduces the main features of the stress-strain behaviour of the material and it is versatile enough to take diffusion damage development modes and residual stress states into account. Furthermore, it offers the possibility to evaluate the impact of changes in microstructures and micromechanical behaviour on the micromechanical behaviour.