Temperature-dependent stiffness of a composite wind turbine blade: experimental investigation at material and structural scales

Abstract

Operation of wind turbines in cold climates involves substantial temperature variations that may affect the mechanical behaviour of composite blades and thereby interfere with structural health monitoring and digital twin applications if not properly accounted for. This study investigates the influence of sub-zero temperature on both material-level properties and global structural stiffness of a composite wind turbine blade. Material characterization was performed using tensile tests on specimens extracted directly from a 12.6 m research blade and tested at four temperature levels between +20 °C and −20 °C. Young’s modulus and Poisson’s ratio were identified to quantify temperature-dependent elastic behaviour. In parallel, static tests were conducted on the full blade inside a large-scale climate chamber under controlled thermal conditions. Quasi-static flap-wise loading was applied incrementally, while the response was measured using strain gauges, displacement sensors, load measurements, and internal temperature monitoring. The coupon-level results revealed substantial specimen-to-specimen scatter, which limited the statistical clarity of the identified temperature trends, although an overall increase in stiffness with decreasing temperature was observed. In contrast, the blade-level tests showed a clear, repeatable, and nearly linear increase in effective stiffness as temperature decreased. The mean structural stiffness change over the investigated temperature range was 2.7%, with good repeatability across measurement channels. Comparison of the two scales highlights that coupon-level trends cannot be directly translated into structural behaviour without accounting for blade architecture and load transfer mechanisms. The findings demonstrate that temperature-induced stiffness variations should be explicitly considered in the interpretation of monitoring data and in the development of reliable digital twins for wind turbines operating in cold climates.