Effects of Shallow Angle on Static Strength and Fatigue Life of Multi-directional Laminates for Wind Turbine Blades

Abstract

The effects of the shallow angle on the static strength and the fatigue life of the multi-directional glass fiber-reinforced plastics for wind turbine blades were presented based on experimental results and predictions. The static tests and the tension-tension fatigue tests under cyclic fatigue loads with a stress ratio of 0.1 were performed on bi-axial (BX, [+/-]), tri-axial 1 (TA, [0/+/-(2)]), and tri-axial 2 (TX, [0(2)/+/-]) laminates with ply angles of 25 degrees, 35 degrees, and 45 degrees. A multiscale approach was applied to predict the static tensile and compressive strengths and the S-N curves of BX, TA, and TX laminates based on the constituents: fiber, matrix, and interface. Three ply-based failure criteria (Hashin, Puck, and Tsai-Wu) were also employed to predict the static strength and compare with the experimental results. The predictions and the experimental results show that the tensile strength increases as becomes shallower, while laminates with a shallow ply angle of 35 degrees showed similar or even lower compressive strengths, especially for TA and TX laminates. The laminate fatigue life increases as becomes shallower. The shallow angle effect on strength and fatigue life is greater for BX than TA and TX laminates since the ply angle plays a more important role in BX. By using the multiscale approach, the shallow angle effect on the laminate static and fatigue behaviors were also explained based on the ply stresses as well as the constitutive micro stresses.