Failure analysis of an elevator drive shaft A. Göksenli * , I.B. Eryürek Faculty of Mechanical Engineering, Istanbul Technical University, Gümüssuyu 34437, Taksim, Istanbul, Turkey article info Article history: Received 23 May 2008 Accepted 25 May 2008 Available online 11 June 2008 Keywords: Drive shaft Elevator Failure analysis Notch effect Finite element method abstract 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 key- way 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 frac- ture 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 cur- vature on stress distribution is explained by using FEM and precautions which have to be taken to prevent a similar failure is clarified. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction The elevator drive shaft investigated in this paper was in service for 30 years. Elevator drive system is mounted at the bottom of the building (Fig. 1). It is reported that no maintenance was applied on the shaft during operation life. The elevator is used in a building consisting of eight floor and 16 apartments. The elevator has a four person (320 kg) capacity. Just before the accident, two persons were leaving the elevator and because of sudden fracture of the shaft, connection between pulley and electric engine was broken, which lead the break system of the engine to fail. Due to the weight of balance weight, ele- vator lifted upwards with a huge speed. During the accident nobody was injured. 2. Analysis of elevator drive system During analysis of elevator drive system, it is concluded that torque, which is produced by an electric motor, is transmit- ted by a worm gear to the shaft. The electric engine, which produces 6.5 HP, is rotating 1500 rpm and reduction ratio of the worm gear is 28.6. The shaft rotates the pulley by a key. The four main ropes of the elevator are placed on the pulley and by revolving in both direction of the drive shaft and pulley, the elevator moves up and down. Service speed of the elevator is 0.6 m/s. The shaft is supported in three points in form of journal bearings (Fig. 2). 1350-6307/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.engfailanal.2008.05.014 * Corresponding author. E-mail addresses: goksenli@itu.edu.tr (A. Göksenli), eryurekb@itu.edu.tr (I.B. Eryürek). Engineering Failure Analysis 16 (2009) 1011–1019 Contents lists available at ScienceDirect Engineering Failure Analysis journal homepage: www.elsevier.com/locate/engfailanal