Abstract. The strength analysis of an existing 5-meter composite wind turbine blade using TsaiWu and Puck failure criteria is presented. Finite element analysis is performed on the blade under static flap wise loading. ANSYS APDL scripting language is used to implement Puck failure criteria and degradation rules for the progressive failure analysis of the blade. Evaluation and visualization of Tsai-Wu inverse reserve factors and Puck failure exposures in the blade is done with the help of the Ansys ACP/Post module. The results of this study indicate that the blade is not able resist extreme load case and needs to be redesigned. Root and trailing edge of the blade have the highest risk of failure initiation. Linear analysis using Tsai-Wu and Puck failure criteria is compared with the nonlinear analysis using progressive Puck failure criteria. It is concluded that progressive analysis is necessary for a more realistic simulation of blade failure mechanisms. Results of the analysis will be used to calibrate structural test set-up of the blade. IntroductionThe long-term reliability of wind turbines is very important for sustainable and economically viable wind energy utilization. Therefore, wind turbine designs must be optimized to minimize costs and maximize lifetime. This requires performance and durability characteristics of wind turbine materials, components and structures to be understood extensively. The most critical component of a wind turbine is the composite rotor blade. A rotor blade failure can have a significant impact on turbine downtime and safety. To avoid a blade failure, knowing the strength of the composite rotor blades is essential. Hence, validation of a composite blade resistance must be checked by structural testing and/or analysis [1]. However, the structural testing methods such as full-scale testing of the blade are expensive and troublesome due to construction of a test set-up. In order to provide more data for structural design and analysis of wind turbine blades, test approaches are being developed [2]. Structural analyses are utilized to calibrate structural blade test set-ups for different loading scenarios.In the literature, there are many studies on the structural behaviour of composite wind turbine blades. For instance, a novel methodology for the structural design and analysis of tidal turbine blade is presented based on the Puck phenomenological failure criteria for fibre and inter-fibre failure [3]. The methodology that is developed in the study predicted damage values for different load cases. This methodology is an iterative design process with respect to failure criteria to check structural strength of the blade. Another study developed is a fatigue damage simulator utilizing the failure criteria and degradation rules of Puck for the life prediction of composites under variable amplitude loading [4]. Puck failure criteria are used to predict failure initiation and sudden stiffness degradation. In another article, structural analysis was performed using finite element method to...