Investigating the effect of work hardening on fatigue performance of fastener steels

Abstract

Bulten group aims to introduce a new line of high performance fasteners, manufactured without the conventional energy intensive heat treatment process. This thesis aims to answer how this highly work hardened material performs with respect to fatigue life. Drawn rods with differing degrees of work hardening were subjected to tensile and fatigue testing. Due to the importance of the surface properties in the material a novel method of notching using an indentation tool was performed. The results indicate an increase in fatigue life for the further work hardened material at elevated loads, likely due to the increase in strength. At lower loads the results show no difference and an increased spread in number of cycles to failure. When the influence of a increase in monotonic yield strength is correct for by relating it the applied stress amplitude, the less drawn material performs better. Finally the possibility of using a Junker vibration testing machine for determining fatigue properties is investigated.