7. Environmental influences on fatigue life

As organic matrices are sensitive to water, environmental conditions (humidity, temperature) coupled with mechanical stress can lead to irreversible degradation, which can severely affect the mechanical strength of composite parts in service. It is therefore imperative to know how the properties of the materials used evolve as they age, in order to predict their service life or strength beyond a given time. The influence of aging on material behavior is manifested by a lowering of the glass transition temperature T _g of the matrix and a drop in mechanical characteristics (shear modulus, transverse modulus, fracture characteristics, etc.).