In general, fretting fatigue may occur in the artificial hip joint and bone cement as a result of the cyclic loading and fretting between these parts. Fretting decreases dynamic durability and produces wear debris, etc. These can cause various effects on the human body and therefore, it is necessary to know the fretting fatigue characteristics of biomaterials in vivo in order to avoid these effects. In this study, plain fatigue and fretting fatigue tests were carried out in air and in vivo environment, that is, in Ringer's solution on Ti-29Nb-13Ta-4.6Zr, which has been developed recently for biomedical materials, and also on conventional biomedical material, Ti-15Mo-5Zr-3Al.
In both low cycle fatigue and high cycle fatigue life regions, fretting fatigue strength of Ti-29Nb-13Ta-4.6Zr and Ti-15Mo-5Zr-3Al subjected to various heat treatments decreases remarkably as compared with their plain fatigue strength. In this case, the decreasing ratio of fatigue life by fretting increases with increasing the crack growth area, which is caused by the tangential force at the contact plane of pad. In fretting fatigue in air, degree of damage by fretting, which is indicated by Pf/Ff where Pf and Ff are the plain fatigue limit and fretting fatigue limit, respectively, increases with increasing elastic modulus and hardness. In fretting fatigue in vivo environment, passive film on specimen surface is destroyed by fretting action even in Ti-29Nb-13Ta-4.6Zr, which has excellent corrosion resistance, and, as a result, corrosion pits that lead to decreasing fretting fatigue strength especially in high cycle fatigue life region, are formed on its surface.