Technische Mechanik - European Journal of Engineering Mechanics
https://journals.ub.ovgu.de/index.php/techmech
<p>The journal is edited by <a href="https://www.matem.ovgu.de/">Magdeburger Verein für Technische Mechanik e.V.</a> and <a href="http://www.ovgu.de/">Otto von Guericke University Magdeburg</a><br />Editor-in-chief: Daniel Juhre<br />Assistant editor-in-chief: Elmar Woschke</p> <p>Institute of Mechanics<br />Otto von Guericke University Magdeburg<br />P.O. Box 4120<br />39016 Magdeburg, Germany<br />Telephone: +49 391 67–52 459<br />Fax: +49 391 67–12 439/–12 863<br />E-Mail: <a href="mailto:Technische.Mechanik@ovgu.de">Technische.Mechanik@ovgu.de</a><br />Internet: <a href="http://journals.ub.uni-magdeburg.de/ubjournals/index.php/techmech">www.ovgu.de/techmech</a></p>Magdeburger Verein für Technische Mechanik e.V. & Otto-von-Guericke-Universität Magdeburgen-USTechnische Mechanik - European Journal of Engineering Mechanics0232-3869Yet another elasto-plasticity formulation
https://journals.ub.ovgu.de/index.php/techmech/article/view/2094
<p>An elasto-plasticity formulation is presented that requires no intermediate (stress-free) configuration, since all describing<br />tensors are solely of proper-Eulerian or proper-Lagrangean type. This formulation - based on commutative-symmetrical elasticplastic stretch tensor products with symmetrizing-rotation tensors in the middle - is discussed and compared with the Bilby-Kröner-Lee formulation, which defines an intermediate (stress-free) configuration that is not well-determined - as noted, e.g., by Casey & Naghdi (1980). For an Eulerian continuum description, it turns out that the symmetric elastic part of the presented formulation (with only proper-Eulerian tensors) has similarities with the elastic tensor factor eF of the Bilby-Kröner-Lee multiplicative elasto-plastic decomposition <strong>F</strong> = <sup>e</sup><strong>F</strong> . <sup>p</sup><strong>F</strong> of the deformation gradient <strong>F</strong>. From a Lagrangean point of view, however, the symmetric elasticity tensors of the two models differ considerably: the elastic right stretch and Cauchy-Green deformation tensor of the new formulation are proper-Lagrangean tensors, while the corresponding tensors of the Bilby-Kröner-Lee formulation are not well-determined, since they refer to an intermediate (stress-free) configuration. As finite orthotropy modeling requires a material reference configuration in which (imaginary) fibers are perpendicular to each other, finite elastic orthotropy and finite plastic orthotropy can only be modeled simultaneously based on proper-Lagrangean elastic and plastic tensors provided by commutative-symmetrical deformation tensor products and not by Bilby-Kröner-Lee formulations.</p>Klaus Heiduschke
Copyright (c) 2023 Klaus Heiduschke
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2023-05-172023-05-1743220321010.24352/UB.OVGU-2023-056A thermo-coupled constitutive model for semi-crystalline polymers at finite strains: Application across scales
https://journals.ub.ovgu.de/index.php/techmech/article/view/2138
<p>Fiber reinforced thermoplastics are widely used for thermoforming and injection moulding processes, since their high strength to mass ratio is favorable for various industrial applications such as, for example, automotive engineering. Semi-crystalline polymers, as the composites matrix material, make up a subcategory of thermoplastics, which partly crystallize after cool-down from the molten state. They are reinforced with glass or carbon fibers to enhance their material performance. Nevertheless,<br />during the thermoforming process, unwanted residual stresses can arise, due to the complex material behavior of semi-crystalline polymers under different temperatures and strain rates. The interaction between matrix and reinforcement being another unknown factor. Therefore, computational models are needed to predict the material response reliably and minimize production errors.<br />This work presents a thermomechanically consistent phenomenological material formulation for thermoplastics at finite strains.<br />In order to account for the highly nonlinear material behavior, elasto-plastic and visco-elastic contributions are combined in the model formulation. To account for the crystalline regions, a hyperelastic-plastic framework is chosen and extended with a tension-compression asymmetry in yielding. The material parameters, characterized using experimental results, depend on both,<br />the temperature as well as the degree of crystallinity. Together with a linear elastic material model for glass fibers, the matrix formulation is embedded in a representative volume element with unidirectional fiber reinforcement to demonstrate the capabilities of the modeling framework in a multiscale context. A comparison of the virtual testing at varying temperatures and degrees of<br />crystallinities to experimentally obtained results is planned as future work.</p>Marie ReuversSameer KulkarniMichael JohlitzAlexander LionTim BrepolsStefanie Reese
Copyright (c) 2023 Marie Reuvers, Sameer Kulkarni, Michael Johlitz, Alexander Lion, Tim Brepols, Stefanie Reese
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2023-06-052023-06-0543221121910.24352/UB.OVGU-2023-057Autoregressive neural networks for predicting the behavior of viscoelastic materials
https://journals.ub.ovgu.de/index.php/techmech/article/view/2166
<p>In the present work, the capabilities of neural networks to describe viscoelastic material behavior are investigated. Using real one-dimensional test data from a tensile test, autoregressive neural networks were trained. The best networks were then used to calculate the stress and the stiffness in displacement- and force-driven simulations. The results were compared with both experimental data and simulation results of a classical material model.<br>The viscoelasticity discussed here plays a special role in the description of complex rubber materials, in addition to long-term effects, failure or heat-induced mechanisms. Classical material models simplify the real behavior, which is the reason for the occurrence of simulation errors. To overcome these limitations, this paper presents a different way of material modeling by describing the strain-stress correlation using a neural network. Previous stress states from the time history are used in the calculation to account for the path-dependent behavior of viscoelastic materials. Other effects, such as the influence of different temperatures, are not addressed in this work, but can be included with an appropriately large training data set.</p>Lukas MaurerFabian DuvigneauDaniel Juhre
Copyright (c) 2023 Lukas Maurer, Fabian Duvigneau, Daniel Juhre
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2023-06-052023-06-0543222022910.24352/UB.OVGU-2023-058Mechanical properties of cookie-shaped auxetics using finite elements and soft robotics appllication
https://journals.ub.ovgu.de/index.php/techmech/article/view/2137
<p>Auxetic materials, which present a negative Poisson ratio and, by extension, an inverse deformation mechanism compared to natural materials, are gaining more and more interest. This interest is due to the unusual characteristics presented by these and are uncommon to natural materials. In this work, through a set of equations, a 4-petal cookie-shaped structure is generated. The generated parametric design is studied with the use of finite element analysis (FEA). Both Poisson's ratio and the stiffness are calculated for every parameter. The minimum value of the Poisson's ratio was found equal to -0.2369 and the stiffness was calculated to have values approximately from 14 to 314 kN/m. After this analysis, as a case study, a grid of the previously generated auxetic structure is placed as an infill of a gripper shaped structure. This application investigates the ability of the structure to hold objects due to its geometry as well as the potentially better distribution of the stresses created within the mesh during the holding process. From the results of the application it is clear that the structure can indeed function as a gripper as well as that the stresses are more evenly distributed along the length of the structure in comparison with another type of auxetic infill.</p>Christos-Gerasimos KoustoumpardisGeorgios Stavroulakis
Copyright (c) 2023 Mr Christos-Gerasimos Koustoumpardis, Georgios Stavroulakis
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2023-06-152023-06-1543223023710.24352/UB.OVGU-2023-059Using a Partially-Linear Simplified Model for Gravitational Three Phase-Flow of Water, Oil and Supercritical C02 in Porous Media
https://journals.ub.ovgu.de/index.php/techmech/article/view/2171
<p lang="en-US">In this article we use a simplified model for vertical three-phase flow in porous media of immiscible fluids like water,<br />oil and supercritical-CO<sub>2</sub>. The relative permeability functions of oil and CO<sub>2</sub> phases are assumed to be linear functions of the<br />respective saturations while the relative permeability of the water phase is a quadratic function of water saturation. For vertical<br />flow (gravity taken into account) and fluids having small density differences, the model intend to represent the case in which phases<br />supercritical-CO<sub>2</sub> and oil are inclined to miscibility when water phase is absent for certain temperature and pressure conditions,<br />while the flow gains some immiscibility properties as the water phase becomes present. This model leads to a 2x2 system of<br />conservation laws which loose strict hyperbolicity at three isolated coincidence points at the edges of the saturation triangle. We<br />use the wave curve method to solve a class of Riemann Problem.</p>Panters Rodriguez Bermudez
Copyright (c) 2023 Panters Rodriguez Bermudez
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2023-10-272023-10-2743223824810.24352/UB.OVGU-2023-060Stability analysis of hygro-magneto-flexo electric functionally graded nanobeams embedded on visco-Pasternak foundation
https://journals.ub.ovgu.de/index.php/techmech/article/view/2164
<p>In this paper, the stability analysis of hygro-magneto-flexo electricity (HMFE) on functionally graded (FG) viscoelastic nanobeams accommodate in viscoelastic foundation based on nonlocal elasticity theory is addressed. Higher order refined beam theory is used for the expositions of the displacement components and the viscoelastic foundation is included with Winkler-Pasternak layer. The governing equations of nonlocal gradient viscoelastic FG nanobeam are obtained by Hamilton's principle and solved by administrating an analytical solution for different boundary conditions. A power-law index model is adopted to describe continuous variation of temperature-dependent material properties of FG nanobeam. A parametric study is presented to inquire the effect of the nonlocal parameter on various physical variables.</p>L. AnithaL. RajalakshmiT. GunasekarJ. Nicholas GeorgeRajendran SelvamaniF. Ebrahimi
Copyright (c) 2023 L. Anitha, L. Rajalakshmi, T. Gunasekar, J. Nicholas George, Rajendran Selvamani, F. Ebrahimi
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2023-11-022023-11-0243224925810.24352/UB.OVGU-2023-061Closed-form series solutions to peridynamic rod equations: Influence of kernel function
https://journals.ub.ovgu.de/index.php/techmech/article/view/2170
<p>Peridynamics is a generalized continuum theory that takes into account long range internal force/moment interactions.<br />The aim of this paper is to derive closed form analytical solutions for peridynamic rod equations with fixed-fixed and fixed-free<br />boundary conditions. A family of kernel functions is introduced to analyze the influence on the results for rods under distributed<br />static load and free vibrations for different initial conditions. To validate the derived solutions, nonlocal results are compared<br />against classical results for different boundary conditions and horizon sizes. One can observe that when the horizon size approaches<br />zero, the results according the non-local and local theories converge to each other. Introduced kernels indeed play different roles in<br />both statics and dynamics. In particular, the Gauss type kernel function gives the results which are closest to the classical solutions.</p>Konstantin NaumenkoZhenghoa YangChien-Ching MaYang Chen
Copyright (c) 2023 Konstantin Naumenko, Zhenghoa Yang, Chien-Ching Ma, Yang Chen
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2023-11-212023-11-2143225927010.24352/UB.OVGU-2023-062