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 δ_c and the failure energy G_c. 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.