Prediction of fatigue damage in tapered laminates

Effective implementation of ply-drops configurations substantially improve the damage tolerant design of flexible and aero-elastic wind turbine blades. Terminating a number of layers for an optimized blade design creates local bending effects. Inter-laminar stress states in tapered areas give rise to delamination and premature structural failure. Precise calculation of the stress levels for embedded ply-drops is required to predict failure initiation within acceptable limits.
Multi-axial stress states in orthotropic laminates subjected to diverse loading mechanisms nucleate microscopic cracks. By increasing the cracks density, damage occurs when residual material properties reduce to a critical level. Residual strength and stiffness of simple laminates are assigned in a set of fatigue failure criteria to assess the remaining life of the components by increasing number of loading cycles. The mode and position of damage initiation in ply-drops area is predicted accordingly.