Fretting & friction induced fatigue failure: damage criterion of polytetrafluoroethylene

Biomedical implants like the hip joint with cup work under continuous friction and wear phenomena where soft materials are suitable for the low coefficient of friction. As continuous, joints go under dynamic fatigue that should be accelerated by the fretting action generated from contact pairs and the inclination angle of the femur. In this research, the fatigue behavior of PTFE has been studied and compared under friction along with fretting action. A FE based Numerical model justified the experimental results. It showed that fretting and friction influence the fatigue life of PTFE by various angles. Fretting pressure optimization was identified as the determinant factor, while the loading point ratio was remarked as an effective parameter for both fretting and friction fatigue. Penetration depths proportionality to corresponding stress observed the effect of fretting fatigue where friction acts in different degrees depending on the geometry (collar/notch)-loading (friction) position. The fractographical demonstration revealed a relation between crack orientation and fretting action. Predefined loading action on test samples justified the singularity of fretting-friction fatigue characteristics on the damage mechanism of PTFE.