In orthopedic surgery and particularly in the total hip arthroplasty (THP), the stem fixation is performed in general using surgical cement which consists essentially of poly (methyl methacrylate) (PMMA). Fracture of cement and prosthesis loosening appears after high concentrations of stress. This phenomenon origin is due to the presence of micro-cavities in the cement volume due to patient movements. The focus of this study is the modeling using the finite element method of a crack emanating from a cavity. It was assumed several positions and orientations of the crack in the cement to calculate the stress intensity factor (SIF). Results show that the presence of a crack emanating from a cavity in the cement increases the risk of fracture of cement.

Cement is the weakest link in the composition of total hip prosthesis in terms of mechanical properties. The knowledge of the intensity and distribution of stresses on the cement attaching the implant to the bone is of great importance for understanding the condition of the prosthesis and its failure. In this study, the finite element method is used to analyze the magnitude and the equivalent Von Mises stress distribution induced in different components of the total hip prosthesis (THP) as well as the identification of the damage induced in the cement and between two cavities located in the polymethyl methacrylate (PMMA). The crack propagation is determined and localized using the extended element method (XFEM). The results show that the fracture stress of the cement in its proximal part is very important. These stresses increase considerably with the interaction of the cavities in this binder, causing damage to the cement and the loosening of the prosthesis.

This research is based on the study of the fatigue behavior of an aluminum alloy plate with a central crack. The plate is subjected to a tensile loading on its lower and upper parts. Several parameters were highlighted, such as the loading effect with a load ratio R = 0. The effects of the load ratio on both the repaired and not repaired plates, by two composite patches, which are boron/epoxy and graphite/epoxy, were investigated, as well as the effect of the plate material on plate life, comparing different materials

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