Creep/fatigue/relaxation of angle-ply GFRP composite laminates

Fiber-reinforced polymer (FRP) composites are used in engineering structures of several domains, such as wind energy, bridges, and automotive industry. Usually such material systems include polymeric matrices and exhibit behavior that is sensitive to the loading pattern due to their cyclic- and time-dependent mechanical properties. Although the majority of the aforementioned engineering applications undergoes a significant number of fatigue cycles, of random loading profiles, throughout their lifetime, the research efforts assigned to the investigation of the loading effects on their fatigue behavior are still very limited. Fatigue design allowables are today derived from standardized experimental investigations, mainly subjecting the examined materials under constant amplitude continuous fatigue loading; not corresponding to actual loading profiles seen by the structures in open air applications. This chapter aims to present the effect of different loading patterns on the fatigue life and damage development of angle-ply thermoset composites, discussing the influence of load interruptions including periods of zero load, when the material recovers, or periods of load hold times, during which the material creeps.