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Near-resonant regimes of a moving load on a pre-stressed incompressible elastic half-space

Kudaibergenov Askar, Kudaibergenov Askat, Prikazchikov Danila

Acta Mechanica et Automatica

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2021

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Vol. 15, no. 1

30--36

EN

The article is concerned with the analysis of the problem for a concentrated line load moving at a constant speed along the surface of a pre-stressed, incompressible, isotropic elastic half-space, within the framework of the plane-strain assumption. The focus is on the near-critical regimes, when the speed of the load is close to that of the surface wave. Both steady-state and transient regimes are considered. Implementation of the hyperbolic–elliptic asymptotic formulation for the surface wave field allows explicit approximate solution for displacement components expressed in terms of the elementary functions, highlighting the resonant nature of the surface wave. Numerical illustrations of the solutions are presented for several material models.

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Natural frequency and bending analysis of heterogeneous polar orthotropic-faced sandwich panels in the existence of in-plane pre-stress

Alipour M. M., Shaban M.

Archives of Civil and Mechanical Engineering

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2020

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Vol. 20, no. 4

174--197

EN

In this paper, the effects of plane pre-stresses on the free vibration and static analyses of circular and annular sandwich panels are examined based on an accurate formulation, as first time. It is assumed that initially pre-stresses consist of in-plane normal (tensile/compressive) and pure bending stresses. New first-order shear deformation theory together with a layerwise approach for sandwich panel is utilized. The sandwich panels are made up of either orthotropic or heterogeneous polar orthotropic materials. Furthermore, piecewise-defined linear local in-plane displacements are adopted based on zigzag theory. The governing partial differential equations are extracted by implementing principle of minimum total potential energy. A unified analytical solution procedure is developed based on power series method for the analysis of heterogeneous initially stressed annular and circular sandwich panels with arbitrary boundary conditions. The transverse shear stress is precisely calculated by considering three-dimensional theory of elasticity. To validate the proposed formulation, the obtained results are compared with those of finite element method. After numerically demonstrating the accuracy of the method, the effects of different geometrical and material parameters, boundary conditions and in-plane pre-stresses on the free vibration and static behavior of circular and annular sandwich panels are investigated.

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Oil Paintings and Mechanics : How To Save Art Treasures Using Knowledge from Dynamics

Kracht K., Wagner U. v.

Machine Dynamics Research

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2011

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Vol. 35, No. 4

49-61

EN

Oil paintings of the old masters are valuable not only for education and social life but also from an economical point of view. These artworks undergo vibrations due to multiple reasons. During exposition there is excitation by public or external traffic load. Higher excitation levels are reached during transports. Consequences may be the emergence of cracks or loss of paint slabs. For protecting an oil painting from damage it is essential to be aware of its condition.Conventional techniques applied by conservators are based on visual detection. In contrastto this, our work is based on knowledge from dynamics applied to this new field. Test objects were prepared by a docent of old painting techniques of Berlin Universityof Arts. They were aged at different levels by a research institution for paint and varnish atMagdeburg. After aging the dummies are investigated for their dynamical behavior usingdifferent excitations (harmonic, broad-band) and measuring dynamic responses. Speciallaser equipment and the experimental set up were developed for measurements on thesurface of painted canvas. Strong influences of the alteration of the dummies andcharacteristic nonlinearities could be observed during these measurements. Cracks wereinitiated during dynamic fatigue tests and correlated with dynamic responses. Acorresponding modeling is based on a Kirchhoff plate with non-constant pre-stress. The presented work should finally lead to condition monitoring of oil paintings and techniques for the prevention of artworks from vibrations.

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Finite element stress analysis of forging dies to improve their fatigue life

Dehghani K., Jafari A.

Materials Science Poland

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2010

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Vol. 28, No. 1

139--152

EN

The forging dies, and in a particular case a bolt die, were stress analyzed by the finite element method. Two possible modes of die failure, due to hoop and axial stresses, were investigated. The critical zones of highly concentrated stresses have been identified. Several approaches were studied to overcome the tensile stresses that result in a premature failure of a forging die. The results of the finite element simulations show that generating the compressive or negative stresses, as produced by the techniques applied, can completely remove, or at least significantly reduce the detrimental tensile stresses generated/ during forging. This can readily improve the fatigue life of dies. Numerical stress analysis was performed on critical elements lying in the transition zone of dies. Finally, advanced numerical methods, especially the finite element method, were used to determine the optimum mean stress and the optimum alternative stress as well as to analyze the compressive negative stresses generated by the applied techniques. The ABAQUS software was used for the finite element simulation. The optimum mean stress and the optimum alternative stress at the most critical finite element were determined to be 140-150 and 34-38 MPa, respectively.