A Stress Compatible Finite Element for Implant/Cement Interface Analyses

Abstract

A new finite element has been developed to enforce normal and shear stress continuity at bimaterial interface points in order to alleviate the problem of high stress discontinuity predictions by the conventional displacement finite element method. The proposed element is based on a five node isoparametric quadrilateral element where the fifth node is located at the interface boundary of the element. A series of validation tests have been carried out to assess the correctness of the stress distribution obtained by the new element at interfaces of highly dissimilar materials. The results of the tests are compared to analytical solutions and to results from convergence studies performed by the conventional finite element method (SAP-IV). Overall, the proposed element has been demonstrated to have a very satisfactory degree of reliability, especially in view of the observed inability of the conventional method to yield interpretable interface stress values for most cases analyzed. Finally, the new interface element has been applied to the analysis of an axisymmetric model of the knee tibial implant. The superiority of the proposed element over the conventional one has been demonstrated in this case by a convergence study.