Compressive stress relaxation behavior of irradiated ultra-high molecular weight polyethylene at 37 degrees C

The preconditioned stress relaxation behavior of irradiated ultra-high molecular weight polyethylene (UHMWPE), a commonly used bearing surface in total joint replacements (TJR), was modelled in uniaxial compression at 37 degrees C. Twenty cylindrical specimens (10 mm dia. x 27 mm length) were machined from a compression molded plate of medical grade UHMWPE and gamma-irradiated to a minimum dose of 2.5 Mrad. At an initial strain rate 1000%/s, five specimens were each tested at constant strains of 1, 2, 5, and 10%. The modified superposition principle provided a good agreement of the nonlinear viscoelastic (stress relaxation) behavior of UHMWPE (standard error of 0.0753 MPa).