Veröffentlichungen in „peer-review“ Journals (2010-..)
List of recent publications |
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Thin-walled rods with semi-open profile for semi-solid automotive suspension International Journal of Automotive Technology, 2012 Volume 13, Number 2, 231-245, DOI: 10.1007/s12239-012-0020-9 A new type of thin-walled rods with a semi-open cross-section is suggested and the optimization performed. Descriptive of this class of thin-walled beam-like structures is the closed but flattened profile. In this work, an intermediate class of thin-walled beam cross sections is studied. The cross-section of the beam is closed, but the shape of the cross-section is elongated and curved. The walls that form the cross section are nearly equidistant. The principle application of the theory of semi-open thin-walled beams is the twist beam of the semi-solid trail arm axle. The analytical expressions for the effective torsion stiffness and effective bending stiffness of the twist beam are derived in terms of section properties of the twist beam with a semi-open cross section. Based on the stiffness coefficients of the twist beam, the roll rate, chamber and lateral rigidity of the suspension are derived.
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Confirmation of Lagrange Hypothesis for Twisted Elastic Rod Structural and Multidisciplinary Optimization, 2012 Volume 42, 2012, DOI: 10.1007/s00158-012-0773-9 The history of structural optimization as an exact science begins possibly with the celebrated Lagrange problem: to find a curve which by its revolution about an axis in its plane determines the rod of greatest efficiency. The Lagrange hypothesis, that the optimal rod possesses the constant cross-section was abandoned for Euler buckling problem. In this Article the Lagrange hypothesis is proved to be valid for Greenhill’s problem of torque buckling. The corresponding isoperimetric inequality is affirmed. |
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On the Lagrangian and instability of medium with defects Meccanica, An Inter national Journal of Theoretical and Applied Mechanics AIMETA, 2011 Volume 47, Issue 3 (2012), Page 745-753, DOI: 10.1007/s11012-011-9480-7 The Article presents the Lagrangian of defects in the solids, equipped with bending and warp.The deformation of such elastic medium with defects is based on Riemann-Cartan geometry in three dimensional space. In the static theory for the media with dislocations and disclinations the possiblechoice of the geometric Lagrangian yield the equations of equilibrium. In this article, the assumed expression for the free energy leading is equal to a volume integral of the scalar function (the Lagrangian) that depends on metric and Ricci tensors only. In the linear elastic isotropic case the elastic potential is a quadratic function of the first and second invariants of strain and warp tensors with two Lame, two mixed and two bending constants. For the linear theory of homogeneous anisotropic elastic medium the elastic potential must be quadratic in warp and strain. The conditions of stability of media with defects are derived, such that the medium in its free state is stable. With the increasing strain the stability conditions could be violated. If the strain in material attains the critical value, the instability in form of emergence of new topological defects occurs. The medium undergoes the spontaneous symmetry breaking in form of emerging topological defects. |
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Analytical Model For Simulation Of Forming Process And Residual Stresses In Helical Springs Wire Forming Technology International, 2011, Vol. 14 ( Part 1 / No.1, Part 2 / No.2, Part 3/ No.3) Residual stress can have a great effect on the properties of a material. This article offers a mathematical theory of residual stresses and strains in helical springs that allows calculating stresses on all manufacturing process steps, particularly during coiling and presetting. In Part 1 of this article, the author looks at the Isotropic Work-Hardening Stress-Strain Law and the theory of elastic-plastic combined bending and torsion of a naturally curved and twisted bar. Complete mathematical analyses are provided. In Part 2 of this article, the author looks at the theory of elastic-plastic combined bending and torsion of naturally curved and twisted bar, application of combined bending and torsion theory for simulation of preset for helical springs and the conclusions. In Part 3, the autor covers application of combined bending and torsion theory for simulation of preset for helical springs and the conclusions. |
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Elastic-plastic work-hardening deformation under combined bending and torsion and residual stresses in helical springs International Journal of Material Forming, 3, 2010, p. 869 - 881 DOI 10.1007/s12289-010-0908-8 Residual stress plays an important role with respect to the operating performance of helical springs. Its effect on the different properties of a material (fatigue, fracture, corrosion, friction, wear, etc.) can be considerable. In the modern design of springs, residual stress has therefore to be taken into account. In the present article, the mathematical theory of residual stresses and strains in helical springs is introduced. The theory of residual stresses in helical springs allows calculating the stresses on all steps of manufacturing process, particularly during the coiling and presetting. |
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“Bubble-and-grain” method and criteria for optimal positioning inhomogeneities in topological optimization Structural and Multidisciplinary Optimization . 40, 2010, p. 117 – 135 DOI 10.1007/s00158-009-0400-6 In the article we propose the enhancement of the topology optimization method, which uses an iterative positioning, orientation and hierarchical shape optimization of subsequently introduced elastic inhomogeneities. The inserted elastic inhomogeneities could be more or less compliant than the elastic medium of the structural element being optimized. One extreme case of the inhomogeneity is the cavity of zero stiffness (“bubble”), while the other limit corresponds to the absolutely rigid inhomogeneity (“grain”). This extension of the topology method requires the generalization of topological derivatives. The topological derivative is an instrument for solving topology optimization problems. Namely, the topological derivative quantifies the sensitivity of a problem when the domain under consideration is perturbed by changing its topological genus. In this article we represent the generalized topological derivatives exploiting the Eshelby approach of effective inhomogeneity. For this purpose we study sensitivity of the optimization functional to the placement of infinitesimally small elliptical inhomogeneity. The sensitivity to the infinitesimal translation of inclusion is quantified by the characteristic function. The infinitesimally small inhomogeneity must be inserted at the point, where the characteristic function attains its extreme value. Next, we examine the sensitivity of the Lagrangian to orientation of ellipse and determine its optimal orientation. Finally, we express the optimal eccentricity of ellipse as the function of averaged principal strains in inhomogeneous medium. The compliance functional plays the role of optimization criterion. Using adjoint variables technique of variational calculus, the results could be extended for arbitrary integral functionals. |
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Theory of optimal residual stresses and defects distribution Structural and Multidisciplinary Optimization . 41, 2010, p. 351 - 370 DOI 10.1007/s00158-009-0431-z Residual stress plays an important role with respect to the operating performance of mechanical parts. Its effect on the different properties of a material (fatigue, fracture, corrosion, friction, wear, etc.) can be considerable. |
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Comments on “Shape and topology optimization for periodic problems part I: the shape and the topological derivative” by Barbarosie C. and Toader A.-M. (Struct. Multidisc. Optim. 40:381–391, 2010) Structural and Multidisciplinary Optimization Verlag Springer Berlin / Heidelberg, 40, 2010 |
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Elastoplastic Stress Analysis and Residual Stresses in Cylindrical Bar Under Combined Bending and Torsion Journal of Manufacturing Science and Engineering, 2011, 133 (4) DOI 10.1115/1.4004496 The excessive stresses during the coiling of helical springs could lead to breakage of the rod. Moreover, the high level of residual stress in the formed helical spring reduces considerably its fatigue life. For the practical estimation of residual and coiling stresses in the helical springs the analytical formulas are necessary. In this paper the analytical solution of the problem of elastic–plastic deformation of cylindrical bar under combined bending and torsion moments is found for a special nonlinear stress–strain law. The obtained solution allows the analysis of the active stresses during the combined bending and twist. Moreover, the residual stresses in the bar after springback are also derived in closed analytical form. The results of this analysis are applied to the actual engineering problem of determination of stresses during the manufacturing of helical coiled springs. A practically important example, describing the manufacturing of helical coiled spring is worked out to illustrate the simplicity achieved in determining the plasticization process and residual stresses. The obtained results match the reported measured values. The developed method does not require numerical simulation and is perfectly suited for programming of coiling machines, estimation of loads during manufacturing of cold-wounded helical springs and for dimensioning and wear calculation of coiling tools. |
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20/09/2011 |
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