Determination of fatigue life under low frequency fatigue loading based on temperature evolution

The wind turbine blades are key components of wind turbines. During the working process, the blades are subjected to fatigue loading, resulting in the failure of wind turbine blades. The surface temperature of blade materials will change when subjected to fatigue loading and the temperature rise rate of blade surface under fatigue loading can be used as an index to predict fatigue life. However, the frequency of fatigue loading on the wind turbine blades is low, the non-adiabatic response under low frequency fatigue loading would lead to temperature dissipation. In this paper, fatigue life prediction under low frequency fatigue loading was studied. Based on the law of energy conservation and the laws of heat conduction, heat convection, heat radiation, the temperature evolution of materials under low frequency fatigue loading was theoretically analyzed. Epoxy resin was selected as testing material and fatigue tests were conducted on epoxy resin specimens. During the fatigue test, the infrared thermal imager was used to monitor the samples surface temperature in real-time. The results show that the predicted life considering temperature dissipation effect is closer to the real life. Meanwhile, the general application of life prediction model is further verified by metal material. This work can be used for predicting the fatigue life of wind turbine blades under low frequency.