Vibration Fatigue Crack Propagation And Numerical Simulation Of TC4 Titanium Alloy Blades

The article mainly researches the Fatigue Crack Propagation Property of the TC4 sheet and the TC4 welded joints while they are under the High-Frequency Resonance State. And it explains the reason for the difference between them. Also, it calculates the Fatigue Crack Propagation Lifetime of one particular aero-engine compressor blade before and after the welding process. And the conclusions are as follows.Using the Pneumatic Specimen Resonance system, it get the formulas of the crack growth rate for the TC4 parent metal, weld metal zone and heat-affected zone of the welded joint by the Micro Plasma Arc Welding. These formulas show that the resistance properties to crack propagation for the welded joints' welded-zone and the heat affected-zone are all better than the TC4 parent metal.By observing the microstructure and analyzing the fracture morphology, it get the conclusion that:(1) In the TC4 parent metal, the crack propagation mechanism is mainly trans-granular fracture, and also inter-granular fracture.(2) In the welded-zone,because of many needle type ?? martensite, the resistance properties to crack propagation is better than the original sheet. Also, the crack propagation mechanism is leaded by inter-granular fracture and helped by trans-granular fracture.(3) In the heat-affected zone, the ?? martensite is shorter and more complex than those in the welded-zone, which leads better propagation resistance. Besides, the mechanism is leaded by trans-granular fracture and helped by inter-granular fracture.Comparing the result with the Fatigue Crack Propagation Lifetime of one particular aero-engine compressor blade before and after the welding process, it finds that the Fatigue Lifetime improves after than before in the top of blade, and both reduces in the middle and bottom of the blades.