Lenka Kunčická

Design, analysis and verification of a knee joint oncological prosthesis finite element model

BACKGROUND The aim of this paper was to design a finite element model for a hinged PROSPON oncological knee endoprosthesis and to verify the model by comparison with ankle flexion angle using knee-bending experimental data obtained previously. METHOD Visible Human Project CT scans were used to create a general lower extremity bones model and to compose a 3D CAD knee joint model to which muscles and ligaments were added. Into the assembly the designed finite element PROSPON prosthesis model was integrated and an analysis focused on the PEEK-OPTIMA hinge pin bushing stress state was carried out. To confirm the stress state analysis results, contact pressure was investigated. The analysis was performed in the knee-bending position within 15.4-69.4° hip joint flexion range. RESULTS The results showed that the maximum stress achieved during the analysis (46.6 MPa) did not exceed the yield strength of the material (90 MPa); the condition of plastic stability was therefore met. The stress state analysis results were confirmed by the distribution of contact pressure during knee-bending. CONCLUSION The applicability of our designed finite element model for the real implant behaviour prediction was proven on the basis of good correlation of the analytical and experimental ankle flexion angle data.

Investigation of Mechanical Properties and Microstructure Development of AZ61 Alloy during Rolling, Forging and ECAP

Results of experiments, focused on development of modified AZ61 alloy structure after hot forming, are summarized in this paper. Microstructure changes of the alloy after rolling and forging at temperatures of 380°C and after ECAP processed at 250°C were observed. After forging, the original grain size was reduced almost 14 times down to a value around 9 μm. After ECAP the grain size reduction was even better, almost 60 times. Important role of the ß-phase (Mg17Al12) in this alloy, during plastic forming, was confirmed. Independently of processing technology, the best final properties of the AZ61 alloy were supported with very fine particles distributed in the Mg matrix. The experiment succeeded in proving the influence of precipitates on restoration processes too.