Analysis of the failure of a PPS polymer cycling support: Microscopy and finite element studies

A PPS polymer injection moulded arm-support for cyclists has been developed to allow cyclists to position their arms parallel with the frame of the bicycle for aerodynamic improvement. The component is therefore subjected to both vertically applied force and laterally applied force. The vertical force comes from the weight of the cyclist transferring down through the shoulder to the elbow and forearm, which rest on the component, and the lateral force arising when the cyclist's arms try to push outwards for either power or stability. A component of this design suffered a sudden-onset fracture failure in-service. It was therefore of interest to understand why the component failed in this manner. The component was analysed by using electron microscopy methods at the fracture surface, performing a thermal testing analysis and mechanical data study of the reinforced PPS material to understand the material behaviour and lastly by using finite element (FE) analysis tools to predict the in-service mechanical fields of stress and strain. The resulting analyses highlighted that the failure was potentially caused by an abnormally high level loading, coupled with the potential for a manufacturing process induced void or defect which then acted as a nucleation site for a crack to propagate in the presence of a stress distribution.