Analysis of Recycle Pump Shaft Fracture Cause

Through hardness test, metallographic observation and fractography, the fracture cause of recycle pump shaft was analyzed. The results showed that fracture mode of recycle pump was muti-crack source fatigue fracture. There was round transition zone and turning marks on machining surface were obvious which form sharp indentation resulting in increasing stress concentration where may be crack source because of ease of crack propagation. Stress concentration region in inner screw was also generating crack location. Microstracture of shaft was F+S,which fatigue resistance was low and crack was easily spreading out. when crack got critical size, shaft cross section can not support the rating load, shaft fractured instantly.