Fatigue failure analysis of a leg press exercise machine

The following paper is an engineering failure analysis of an adjustment pin used in a leg press exercise machine. The pin is used to allow adjustment of the machine for people of different heights. It was modeled as a cantilever beam subjected to varying forces depending on the weight stack setting. The fracture occurred at a point of localized stress concentration. The analysis shows an elastic stress concentration of 1.67 which would cause plastic deformation and a fatigue stress concentration of 1.38 that led to the eventual fatigue failure. Based on actual user data, a block loading analysis was used to calculate a pin lifetime of approximately one year. The pin actually failed after 1 years of use. Design changes are recommended to reduce the size of the stress concentration and subsequently increase the life of the adjustment pin.