Abstract
This investigation reports analysis of fracture by splitting a car's front wheel drive shaft into two parts, which ruptured at a very early stage (<10 cycles) of its endurance/driving test. Besides computations for shear stress and shear strength, a number of experimental techniques, e. g. non-destructive testing (ultrasonic flaw detection), chemical and metallographic analyses, hardness measurements, scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) techniques, are used to determine the cause of the drive shaft's fracture. Non-destructive testing results showed the absence of any internal crack or flaw in the failed component, thereby excluding possibility of fast fracture due to propagation of crack. Scanning electron microscopy fractographs showed cleavage fracture at the outer surface of the shaft, whereas chemical analysis results showed that the steel used in the drive shaft conforms to mild steel. On the basis of the design calculations, it is concluded that failure of the shaft occurs due to shear overstressing. On the basis of hardness profile, it is concluded that the shaft has been casehardened by induction hardening. It is recommended that the steel of 25CrMo4/27CD4 type should be selected in the manufacturing of drive shaft, which should be casehardened by carbonitriding for application in modern cars.