Fibre reinforced plastics and especially carbon fibre reinforced plastics (CFRP) exhibit very good weight specific mechanical properties and play an important role in the reduction of structural weight. However, the prediction of the fatigue life of components made of fibre reinforced plastics (FRP) under arbitrary cyclical load is a challenge which is still not met. For the reliable design of such components, an elaborate understanding of the damage process in the material and its effects on the load carrying capacity of the structure is inevitable. Since FRP are a hierarchical and inhomogeneous class of materials, damage phenomena occur on different lengths scales altering the material properties as well as the material state. From an engineering point of view micro damage cracks and flaws in the matrix and at the fibre/matrix interface as well as ruptured filaments are the initial damage mechanism under static as well as cyclic loads. The accumulation of these micro damages provoke failure phenomena on the meso level such as inter fibre failure and interact with the strengths of plies.
In this paper experimental and numerical results on the micro damage evolution under static as well as cyclic loads will be presented and discussed. The damage evolution was investigated experimentally using non-destructive acoustic emission testing and focusses on the damage evolution under transverse cyclic loads. Micromechanical numerical investigations are used to enhance the understanding of the underlying damage processes in the material. The results show, that damage phenomena, initiation limits and evolution depend highly upon the load path.