Since the evolution of fatigue damage in composite materials currently used for large structure, including wind turbine blade, was not well understood, large safety factors were employed which lead to highly conservative designs. In order to improve and enhance the design confidence, these structures were tested in different conditions, which would lead to a lot of time and cost. To advancing, researchers used analytically and simulation methods to design structures. A lot of analytical methods have been proposed for designing and estimating the life of composite structure, one of which was estimation of stiffness reduction in material because of damage. This study investigates one simulation method based on multi-scale damage mechanic, Computational micromechanics was coupled within a continuum damage mechanics (CDM) framework, and implemented through a user-de?ned subroutine within commercial ?nite element software, for evaluating sub-critical damage evolution and stiffness degradation of the structure. Finally, VUMAT user subroutine of ABAQUS is used to determine the constitution equation in continuum damage mechanics and then is applied to wind turbine blade to investigate fatigue damage mechanism.using modified Puck’s criteria, damage is studied in a layer level of a fatigue loaded wind turbine blade. Damage is investigated in fiber direction and matrix. The model is implemented in a user material finite element subroutine to calculate damage parameter in layer level at any cycle of loading. Then, calculations are extended to laminate using Keywords synergistic damage mechanic, Computational micro-mechanic, Continuum damage mechanics, fatigue damage, Matrix cracking.
