1. Fatigue degradation mechanisms

When a laminated composite structure is subjected to stress, the degradation of its properties takes effect well before failure. Moreover, when the structure is highly anisotropic, as is the case with high-performance composites, the geometry of the defects no longer depends on the loading mode, as is generally the case with metallic materials, but mainly on the geometric arrangement of the composite's constituents.

The same damage patterns, typical of unidirectional laminated structures, develop under both static and fatigue loading. At different material scales, this damage is characterized by :

• on a microscopic scale, by loss of adhesion between...