Case study of fail of machinery drive shaft

Abstract

The failure analysis on the drive shaft is reported. Mechanism of the internally initiated failure was discussed in terms of fractgraphy and internal residual stress distribution. The crack was initiated at the existed casting defect. This internal defect caused a brittle crack propagation and the crack stopped still inside the shaft. The area of this brittle failure inside the shaft corresponds to the area where the tensile residual stress distributed. The estimation of brittle failure stress using fracture mechanics showed that the measured tensile residual stress of 400MPa near the center of the shaft was almost enough to start the brittle crack propagation from the internal defect. It was concluded that the crack initiated near the center of the shaft propagated by the residual tensile stress to the certain size, then finally failed by fatigue caused by the external operating force applied on to the shaft.