Performance simulation of a composite orthopedic implant device

Abstract

The static strength and long-term performance of composite hip prostheses under complex mechanical and environmental loading conditions are studied through theoretical modelling and experimental investigations. Two static strength models, namely, a cantilever beam model and an elastic foundation model, were developed using a strength of materials approach, and were transformed into an operating computer code which can be used for stress analysis and engineering design of composite prostheses. The predictions of the two models are shown to be in very good agreement with experimental data. A dynamic, mechanistic cumulative damage model that is capable of predicting the residual strength and life of a composite prosthesis under cyclic loading was also developed, based on a 'Critical Element Model' and the static strength models, and was transformed into an operating computer code. The predictions by the dynamic model are, in general, within engineering accuracy when compared to the experimental data. A test fixture was designed to perform fatigue tests on the composite prostheses. A total of nine prostheses were fatigue tested. Several nondestructive evaluation (NDE) techniques were used to assess fatigue damage development in the specimens tested. Among all the NDE techniques used, x-ray radiography and a surface replication technique were shown to be most effective qualitatively. Destructive tests were also performed on selected specimens, the results are complimentary to the information obtained from the NOE tests.