To increase the long-term performance of
total joint replacements, finite
element analyses of
ultra high molecular weight polyethylene (
UHMWPE) components have been conducted to predict the effect of load on the stress and strain distributions occurring on and within these components. Early models incorporated the monotonic behavior of
UHMWPE without considering the unloading and cyclic loading behavior. However,
UHMWPE components undergo cyclic loading during use and at least two wear damage modes (pitting and delamination) are thought to be associated with the
fatigue fracture properties of
UHMWPE. The objective of this study was to examine the fully reversed uniaxial tension/compression cyclic steady state stress-strain behavior of
UHMWPE as a first step towards developing a cyclic constitutive relationship for
UHMWPE. The hypothesis that cycling results in a permanent change in the stress-strain relationship, that is, that the cyclic steady state represents a new cyclically stabilized state, was examined. It was found that, like other ductile
polymers,
UHMWPE substantially cyclically softens under fully reversed uniaxial straining. More cyclic softening occurred in tension than in compression. Furthermore, cyclic steady state was attained, but not cyclic stability. It is suggested that it may be more appropriate to base a material constitutive relationship for
UHMWPE for finite
element analyses of components upon a cyclically modified stress-strain relationship.