Effect of curved surface of a shoulder fillet round bar on stress concentration factor for axial tension loading

Abstract

In industries, the shoulder fillet round bar (step shaft) is used to transmit the power and motion to fulfil the requirements of a specific application. A step is provided on the shaft for mounting bearings, sprockets, flywheels, pulleys etc. A step on the round bar behaves as discontinuity. The local stresses developed in the vicinity of the discontinuity, known as stress concentration (SC). The SC is one of the major factors responsible for failure of the mechanical component having discontinuity like step shaft. The shoulder fillet is provided in a step to reduce stress concentration on the shaft. The stress concentration can be measured using the stress concentration factor (SCF). The SCF can be calculated with the help of a fringe pattern. In the present research, experimentally, the fringe pattern was not obtained on the shoulder fillet round bar due to the curved surface of the bar. To overcome this problem, a partial slicing model approach was used. Even though, the obtained fringe patterns were not clear due to the sharp corners present in the partial slicing models. The SCF can be calculated with the help of a fringe pattern. These limitations can be overcome using Finite Element Analysis (FEA) and full slicing approaches. In the present research, the FEA was performed on the flat and curved plate (slice). The Rapport factor (RF) was derived for all possible D/d ratios and determined the effect of a curved surface by finding the equivalent SCF of the shoulder fillet round bar. The FEA results of SCF were validated using the Peterson graph and considered acceptable as per the prevalent industry practices. The present study may help the design engineer to find the minimum SCF for the design of the shoulder fillet round bar for the concerned application. It will reduce the design iterations and chances of failure of the shoulder fillet round bar during its operation.