  Lifecycle assessment of wind turbines is essential to improve their design
and to optimum maintenance plans for preventing failures during the design
life. A critical element of wind turbines is the composite blade due to
uncertain cyclic wind loads with relatively high frequency and amplitude in
offshore environments. It is critical to detect the wind fatigue damage
evolution in composite blades before they fail catastrophically and destroy the
entire wind turbines. This study presents a methodology for analysing the
fatigue failure probability of a wind turbine composite blade by using
monitoring stochastic deterioration modelling. On the basis of 5 minutes mean
wind speed measurements, the internal stresses can be accurately obtained from
finite element analysis, and failure probabilities are predicted by stochastic
gamma process fatigue damage model in design service life. A numerical example
of a wind turbine composite blade is investigated to show the applicability of
the proposed model. The results show that the stochastic fatigue damage model
can give reliable results for time-dependent reliability analysis for composite
blades of wind turbines.
