ÚMVI-odbor mechaniky a designu materiálů

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    Shift of S-N curves in some fatigue models due to loading cycle asymmetry
    (Elsevier, 2024-02-15) Kohout, Jan; Věchet, Stanislav
    Fatigue (Wohler's or S-N) curves are usually represented by upper stress of loading cycle in dependence on the logarithm of numbers of cycles to fracture. Increasing mean stress of loading cycle causes a shift of these curves towards higher values of fatigue strength. A successful quantitative description of the high cycle shift was published by Walker. The aim of the paper consists in deriving and verifying the relations describing the shift of fatigue curves in the whole cycle region from ultimate tensile stress to permanent fatigue limit, for the Palmgren, the Kohout-Vechet and the logistic S-N models, using the high-cycle Walker approach.
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    Numerical and Experimental Evaluation of Structured Material for Use in Multi-scale Topology Optimization
    (Wiley-VCH GmbH, 2024-05-15) Vaverka, Ondřej; Červinek, Ondřej; Jaroš, Jan; Koutný, Daniel; Pantělejev, Libor
    Multi-scale topology optimization is a powerful tool for engineers seeking a design with minimum weight and maximum stiffness, using a structured material in the form of a lattice structure. Furthermore, the current trend is to combine multiple lattice topologies in one component to achieve the best possible response to local loading conditions while minimizing weight. Therefore, in this study, a numerical and experimental evaluation by compression tests in two directions is performed for six basic lattice topologies and two hypotheses are tested. The first hypothesis states that an additional weight saving of more than 30% can be achieved by a better choice of lattice topology. The second hypothesis is based on the manufacturing limitations of the Laser Powder Bed Fusion technology and the assumption that a favorable loading direction parallel to the building direction exists. The first hypothesis is only confirmed for loading in the direction parallel to the building direction and the second only for two lattice topologies. When both hypotheses are combined, the additional weight reduction of the multi-scale topology optimization result is 44.5% according to the numerical results and 32.7% according to the experimental verification.