Modelling the mixed-mode failure of cement–bone interfaces

The main purpose of this study is the development of a failure model for the cement–bone interface in cemented hip prostheses. The model includes the mechanical behaviour of the cement–bone interface under mixed-mode loading, reproducing the initial linear behaviour up to a certain stress level, followed by an exponential strain-softening region. Four parameters for each stress mode (tension and shear) must be defined in order to fully characterize this mechanical behaviour: the interface strength t0, the initial stiffness K0, the interface displacement corresponding to full debonding of the interface δc and the failure energy Gc. To validate the potential of the associated numerical model, several tests were simulated, obtaining results close to the experimental ones. This formulation was also applied to simulate a more biomechanical although still academic problem: the debonding evolution of the bone–cement interface of the Exeter total hip arthroplasty system, including fatigue failure of the interface. We conclude that the mixed-mode failure interface model here proposed allows for more realistic simulations of the debonding process of cement–bone interfaces.