Stability Loss Analysis for Thin-Walled Shells with Elliptical Cross-Sectional Area.

The aim of the scientific contribution is to point out the possibility of applicability of cylindrical shells with a constant elliptical cross-sectional shape for stability loss analysis. The solution to the problem consists of two approaches. The first approach is the experimental measurement of critical force levels, where the work also describes the method of production of the sample and jigs that cause the desired elliptical shape. The second approach is solving the problem in the use of numerical methods-the finite strip method together with the finite element method.

A comparison of experimental compressive axial loading testing with a numerical simulation of topologically optimized cervical implants made by selective laser melting.

In recent years, the number of cervical interventions has increased. The stress shielding effect is a serious complication in cervical spine interventions. Topological optimization is based on finite element method structural analysis and numerical simulations. The generated design of cervical implants is made from Ti6Al4V powder by selective laser melting while the optimized cage is numerically tested for compressive axial loading and the results are compared with experimental measurement. Additive manufacturing technologies and new software possibilities in the field of structural analysis, which use the finite element method tools, help to execute implant topological optimization that is useful for clinical practice. The inner structures of the implant would be impossible to make by conventional manufacturing technologies. The resulting implant design, after modification, must fulfill strict application criteria for the area of cervical spine with respect to its material and biomechanical properties. The aim of this work was to alter the mechanical properties of the cervical intervertebral cage to address the clinical concern of the stress shielding effect by topological optimization. A methodology of cervical implant compressive axial loading numerical simulation was created, and subsequent experimental testing was done to obtain real material properties after a selective laser melting process. The weight of the optimized implant was reduced by 28.92 %. Results of the experimental testing and numerical simulation of topologically optimized design showed 10-times lower stiffness compared to the solid cage design, and the real yield strength of the optimized structure is 843.8 MPa based on experimental results.