Local damages in the hip joint endoprosthesis from the с/с composite during overloads

The paper investigates the process of local damages in the hip joint endoprosthesis (HJ) made of unidirectional carbon-carbon composite material (C/C composite) with pyrolytic carbon (PС) matrix. A mathematical model of deformation of the endoprosthesis from the C/C composite has been developed taking into account the processes of local damage. These damages are possible due to overloads, which may be caused by accidental circumstances during human movements. The developed model is a synthesis of an algorithmic model that takes into account the heterogeneity of the pyrocarbon matrix and composite, and an engineering computational model of the biomechanical endoprosthesis-femur system. The matrix algorithm solves the stochastic boundary-value problem of finding mesostresses in PС grains taking into account possible damages. The result of this algorithm is the probability distribution densities for meso-stresses in PС crystallites and the properties of the damaged matrix. The results of calculations based on the engineering model are the fields of macrostrains and macrostresses. At each step of loading of the endoprosthesis, the state of the matrix is monitored and the effective modules of the carbon composite are changed. This is implemented by a continuous exchange of data between the two algorithms, the recalculation of the properties of the composite, which are the input data for the engineering model. The continuous change in the effective properties of the C/C composite during deformation is replaced by a stepwise change. To do this, the volume of the endoprosthesis was divided into areas in which the properties become variable, starting with a certain loading step. The areas of change were determined based on the distribution patterns of macrodeformation fields. A nonlinear loading diagram of the endoprosthesis is constructed taking into account the damage. It is shown that the destruction of the carbon part of the prosthesis begins with local damage, which gradually engulfs the neighboring areas. Damage occurs when the standard load exceeds 1740 Newtons. The maximum force response of the prosthesis to an external load is equal to 2004 newtons. The deformation of the prosthesis at the stage of a critical reduction in load-bearing capacity exceeds the deformation at standard load by 16 %. The high reliability of the considered variant of the endoprosthesis was confirmed, the absence of catostrophic sharp decreases in load-bearing capacity under a significant excess of standard loads was confirmed.