Fatigue characterization of a hydroxyapatite-reinforced polyethylene composite. I. Uniaxial fatigue.

The fatigue behavior of 40 volume % hydroxyapatite-reinforced polyethylene composite (HAPEXtrade mark) at 37 degrees C in saline was determined. S-N curves for this material, both in fully reversed axial tension-compression and fully reversed torsion, have been established. In tension, the cycles to failure ranged from 1000 cycles at 13 MPa to more than 1 million cycles at 4.4 MPa while in torsion they ranged from 100 cycles at 14.4 MPa to more than 1 million cycles at 4.8 MPa. Changes in strain range, tangent modulus, and cyclic energy dissipated during fatigue loading also were examined. Torsional fatigue was found to be considerably more damaging than axial fatigue. The fatigue damage accumulation process occurring in the composite was monitored by observing the reduction in modulus and the increase in energy dissipated. Copyright 2000 John Wiley & Sons, Inc.