A parallel has been made between the design and the failure of some composite structures, such as pressure vessels, and that of a unidirectional carbon fibre-reinforced epoxy resin. This type of composite has many characteristics that make it attractive, however, long-term damage accumulation in it, when under load, is not understood in any quantitative manner. It is therefore necessary to identify the processes involved in the degradation of the composite when subjected to long-term loading. Acoustic emission (AE) has been used to detect damage in the composite material and to relate the microstructural damage processes to the activity recorded from composite specimens through the development of a detailed analytical model of the damage processes involved. A multiscale model beginning at the scale of individual fibres and the surrounding matrix has been developed by taking into account the accumulated effects of individual fibre breaks on the behaviour of the whole composite and therefore explains the AE detected during the tests.