Fracture Analysis of Cooling Fan Blade

All blades of a cooling fan fractured during test. The failure mode and cause were analyzed by appearance observation, metallographic examination and hardness testing of the blades, as well as macro-and-micro observation of the fracture surface. The results show that the main characters in the fatigue crack propagation stage of the blades are beach marks and fine fatigue striations distributed at the zone between beach marks. Low-and-high cycle combined fatigue occurred to the blade. High centrifugal force combined with vibration stress caused low-and-high cycle combined fatigue of the blades. At last, improvement measures were proposed: improve structure of the blades in order to increase bearing capacity, decrease vibration stress of the blades, strictly control the casting quality, and carry out surface treatment of the blades in order to improve its fatigue resistance.