In this paper a stabilized finite element method to deal with incompressibility in solid mechanics is presented. A mixed formulation involving pressure and displacement fields is used and a continuous linear interpolation is considered for both fields. To overcome the Babu s ska-Brezzi condition, a stabilization technique based on the orthogonal sub-scale method is introduced. The main advantage of the method is the possibility of using linear triangular or tetrahedral finite elements, which are easy to generate for real industrial applications. Results are compared with standard Galerkin and Q1P0 mixed formulations for nearly incompressible problems in the context of linear elasticity.
This paper exploits the concept of orthogonal sub-grid scales to stabilize the behaviour of mixed linear/linear simplicial elements (triangles and tetrahedra) in incompressible or nearly incompressible situations. Both incompressible elastic and J2-plastic constitutive behaviours have been considered. The different assumptions and approximations used to derive the method are exposed. Implementation and computational aspects are also discussed, showing that a robust application of the proposed formulation is feasible. Numerical examples show that the elements derived are free of volumetric locking and spurious oscillations of the pressure, and that the results obtained compare favourably with those obtained with the Q1P0 quadrilateral.
3D-printing technologies have greatly influenced the field of fabrication of medical devices. In particular, Fused Deposition Modeling 3D printing has emerged as one the most popular and most promising technologies for fabricating upper-limb prostheses. Over the last years, a variety of types and designs of 3D-printed hand prostheses have been created and are commercially available. However, there are no standards or established procedures for testing these devices. Available information regarding their long-term performance and functionality is very limited. This paper presents a case study of mechanical testing methods applied to a specific design of an upper-limb prosthesis. The device and its subassemblies were subjected to flexion test in hyperextension and abduction conditions, fatigue/wear test, and tensile test. The experimental results are presented and examined. Testing procedures, adaptations and recommendations are described and discussed to demonstrate ways of generating reliable data that serve for comparison among different hand prostheses designs.
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