The optimal shape of metal stem, based on the Finite Element Method and the Gradient Projection Method, was investigated in order to minimize the stress concentration in the cement layer.
A new equivalent 2-D FEM model was proposed here and their result was compared with 3-D FEM analysis using ANSYS. From this 2-D model the optimal shape minimizing the stress concentration in the cement layer was determined by the Gradient Projection Method and checked its validity by 3-D FEM analysis. The constraints considered were the limit on the stresses in the bone and the stem, and the thickness of the stem.
The optimal shape of the stem was found to be thin in its distal part and thick in its proximal part with the exception at the end of the proximal part. In this end region, the cement stress became smaller as the stem got thinner.
Cement의 응력집중을 최소화하여 loosening방지를 위한 인공고관절의 stem의 형상을 구했다.
인공고관절계를 3-D FEM응력해석을 했고 그 결과를 바탕으로 2-D Equivalent Stiffness FEM모델을 선정했고 Gradient Projection Method를 이용하여 최적설계를 했다.
얻어진 stem의 최적형상을 볼때 distal 부에서는 가늘어지고 proximal 부에서는 굵어지며 proximal 끝단에서는 stem-cement 경계의 cement응력을 줄이기 위해 stem이 허용응력범위내에서 가늘어지는 형상을 얻었다.
