Ústav mechaniky těles, mechatroniky a biomechaniky

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    Size Effect on the Ductile Fracture of the Aluminium Alloy 2024-T351
    (Springer Nature, 2024-09-10) Šebek, František; Salvet, Patrik; Boháč, Petr; Adámek, Roman; Věchet, Stanislav; Návrat, Tomáš; Zapletal, Josef; Ganjiani, Mehdi
    Background Reliably calibrated criteria are needed for an accurate prediction of fracture of various components. However, there is not always a sufficient amount of material available. Therefore, miniature testing provides an alternative that is researched together with the following calibration of the ductile fracture criteria and investigating the size effect. Objective The aim is to design miniature testing equipment and specimens for tensile testing, which covers various stress states. This is supplemented by the small punch test, which has the same specimen thickness, taken from the literature to broaden the portfolio for calibration. The second part deals with conducting the finite element analysis, which provided a basis for the calibration of the phenomenological ductile fracture criterion applicable to crack-free bodies to indicate the crack initiation. Methods The steel frame to test thin specimens is designed with optical measurement of deformations. The finite element method is used, within Abaqus and user subroutines, to simulate the tests to obtain the variables needed for the calibration. In addition, the calibration of the criterion using machine learning is explored. Results The feasibility of the proposed experimental program is tested on the aluminium alloy 2024-T351. Moreover, the numerical simulations, which showed a good match with experiments in terms of force responses, adds to the knowledge of modelling in the scope of continuum damage mechanics. Conclusions The presented results provide a material basis for the aluminium alloy studied on a lower scale, while they broaden the testing possibilities and analyses the calibration strategies for the best failure predictability possible.
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    Small-scale domain switching near sharp piezoelectric bi-material notches
    (Springer Nature, 2025-03-08) Hrstka, Miroslav; Kotoul, Michal; Profant, Tomáš; Kianicová, Marta
    Assuming a scenario of small-scale domain switching, the dimensions and configuration of the domain switching region preceding a clearly defined primarily monoclinic piezoelectric bi-material notch are determined by embracing the energetic switching principle and micromechanical domain switching framework proposed by Hwang et al. (Acta Metall Mater 43(5):2073-2084, 1995. https://doi.org/10.1016/0956-7151(94)00379-V) for a given set of materials, structure, and polarization alignment. The piezoelectric bi-material under consideration comprises piezoelectric ceramics PZT-5H and BaTiO3. The analysis of the asymptotic in-plane field around a bi-material sharp notch is conducted utilizing the extended Lekhnitskii-Eshelby-Stroh formalism (Ting in Anisotropic elasticity, Oxford University Press. 1996. https://doi.org/10.1093/oso/9780195074475.001.0001). Subsequently, the boundary value problem with the prescribed spontaneous strain and polarization within the switching domain is solved and their influence on the in-plane intensity of singularity at the tip of interface crack is computed. The effects of the initial poling direction on the resulting variation of the energy release rates are discussed.
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    Multidisciplinary Design Optimization Framework for Morphing Wing using Metamaterials
    (IEEE, 2025-01-28) Zikmund, Pavel; Kofler, Michael; Navrátil, Jan; Hrstka, Miroslav; Pollák, Jakub; Van Kampen, Erik-Jan
    Metamaterials offer innovative potential for morphing wing design. This study investigates two approaches: a variable-stiffness leading edge and a trailing edge with a metamaterial lattice hinge, applying Multidisciplinary Design Optimization to compare these designs against a conventional composite wing. Aerodynamic, structural, and control analyses are integrated, with initial findings bridging 2D aero-structural wing rib design and 3D aerodynamic and control evaluations.
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    A modification of Holzapfel-Ogden hyperelastic model of myocardium better describing its passive mechanical behavior
    (ELSEVIER, 2025-02-21) Vaverka, Jiří; Burša, Jiří
    The passive mechanical behavior of the myocardium is usually mathematically described within the framework of hyperelasticity. One of the most popular models of this kind is that proposed by Holzapfel and Ogden in 2009. It is an orthotropic model formulated in terms of a reasonably selected set of scalar invariants representing different components of the myocardium. Several modifications of the model have emerged over the years. In this paper, we present another one which is characterized by an innovative approach to the modeling of myocardial "sheets", i.e. lamellar collagenous structures that endow the myocardium with orthotropic mechanical properties. We describe their contribution by means of a less common scalar invariant which expresses the change of area of an oriented planar element (representing the plane of a sheet). To compare our formulation with the original model, we matched both of them to the biaxial tension and simple shear experimental data from the literature using a nonlinear least-squares optimization algorithm. The objective function for each model included both biaxial and simple shear data in order to obtain a single set of parameters for both deformation modes. The results show that our modified model can accurately describe both types of tests. The total residual is lowered by approximately 80% by our modification and R2 increases from 0.877 to 0.978 which demonstrates the significance of our modification on the quality of the fit.
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    Influence of Berkovich indenter tilt on the projected contact area at nanoindentation test
    (Brno University of Technology, 2024-05-14) Kovář, Jaroslav; Fuis, Vladimír
    At the nanoindentation test, the tilt of the indenter or specimen surface can occur. This deviation influences the projected contact area, which is important for the evaluation of the Young modulus and hardness. This paper is aimed on the derivation of the analytical expressions for the projected contact area if the indenter is tilted in 3D space. Then the projected contact area is the same as the area of indenter cross-section by the plane corresponding to the specimen surface. The calculated results for tilted and ideal indenter were compared and the influence of the indenter tilt was evaluated. The cross-sections were plotted for few indenter tilts to better describe the change of the projected contact area. The results show that indenter tilt can have significant impact on the results if the indenter tilt is big enough