Evaluation of a new green composite solution for wind turbine blades

The wind energy market requires reliable wind turbines with a long and efficient working life, able to generate energy without interruption, at the lowest investment and operating cost. The current material systems used for making wind turbine blades are in majority based on glass fibres and epoxy resins. These thermoset polymer composites with synthetic fibres have proved to be technologically mature and easy to work with during the manufacturing steps, with highly fluid resin that adheres well to the composites reinforcement fibres. However, glass fibre reinforced plastics show shortcomings, such as relatively high fibre density (approximately 40–50% higher than natural fibres), difficulty to be machined and limited recycling options, not to mention the potential health hazards posed by glass fibre particulates. Among its objectives, the SoftWind project should evaluate new green composite solutions that will lead to the design of recyclable and repairable blades with higher mechanical strength and lower weight than blades made of standard materials. Initially, to familiarise with natural fibres, specimens made of hemp fibres embedded in a vinylester matrix were tested in tension, flexure and impact, and compared with traditional glass fibres with different resins to validate their performance characteristics. Hemp fibres are good candidates for this use, since they offer a sufficient compatibility with technical matrices used in impact-resistant applications. This work validates on hemp/vinylester composite plates an analytical model previously introduced in the literature for synthetic composites when subjected to low-velocity/large-mass impacts. The validation is performed by comparison between the derived analytical load curves and the experimental ones. Moreover, in view of the final scope of modelling the behaviour of a full-scale blade under workloads, the obtained mechanical properties are also used to reproduce numerically, through a finite element code, the damage mechanisms of such bio-based composites.