Failure analysis of an elevator drive shaft

In this study failure analysis of an elevator drive shaft is analyzed in detail. Failure occurred at the keyway of the shaft. Microstructural, mechanical and chemical properties of the shaft are determined. After visual investigation of the fracture surface it is concluded that fracture occurred due to torsional-bending fatigue. Fatigue crack has initiated at the keyway edge. Considering elevator and driving systems, forces and torques acting on the shaft are determined; stresses occurring at the failure surface are calculated. Stress analysis is also carried out by using finite element method (FEM) and the results are compared with the calculated values. Endurance limit and fatigue safety factor is calculated, fatigue cycle analysis of the shaft is estimated. Reason for failure is investigated and concluded that fracture occurred due to faulty design or manufacturing of the keyway (low radius of curvature at keyway corner, causing high notch effect). In conclusion effect of change in radius of curvature on stress distribution is explained by using FEM and precautions which have to be taken to prevent a similar failure is clarified.