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The development of a new composite that is compounded of natural fibres and of a low price polymer, such as HDPE or PP, began in the last decade of the past century. While this is a rather new material no attempts have been made to... more
The development of a new composite that is compounded of natural fibres and of a low price polymer, such as HDPE or PP, began in the last decade of the past century. While this is a rather new material no attempts have been made to analytically describe and simulate mechanical properties of this material. There is also a great lack of knowledge in describing fine tuned processing parameters. Therefore, in the first part of this article micromechanical approach based upon Generalised Method of Cells (GMC) is introduced to simulate properties of injection moulded wood-plastic composite compounded of polypropylene (PP) or polystyrene (PS) and of wood or cellulose short fibres. Materials have first been scanned with an optical and electron microscope to determine average fibre properties and their scatter. These values are then used to determine elastic and plastic response of the composite alongside with its tensile strength and maximum elongation, where the Tsai-Hill failure criterion...
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This paper presents the experimental and numerical results for the flow around a sphere at subcritical Reynolds number of 50 000. Two experimental techniques, the hot-wire and the laser-doppler anemometry (HWA and LDA), are used to obtain... more
This paper presents the experimental and numerical results for the flow around a sphere at subcritical Reynolds number of 50 000. Two experimental techniques, the hot-wire and the laser-doppler anemometry (HWA and LDA), are used to obtain the mean velocity field and the turbulence quantities. These two experiments provided very similar results. Results of a large-eddy simulation (LES) and several Reynolds-averaged Navier-Stokes (RANS) equation models are compared to the experimental results. The LES results are in reasonable agreement with experiments while RANS underpredict the drag coefficient up to 50% compared to experiments and turbulence quantities were predicted far from the experimental values.
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This work analitically and experimentally investigates nonlinear snap-through of a simple class of elastic space trusses in the shape of a regular pyramid. Joints located at the vertices of the base polygon are pinned while the joint at... more
This work analitically and experimentally investigates nonlinear snap-through of a simple class of elastic space trusses in the shape of a regular pyramid. Joints located at the vertices of the base polygon are pinned while the joint at the apex is subjected to a proportionally increasing load acting in the vertical direction. A pyramid truss model has been designed, machined and successfully tested in learning environments to facilitate understanding of the mechanics of truss structures, geometric nonlinearity and stability. Solutions are derived for each load condition under the common hypotheses of linear material law, small or moderate axial deformation in bars and large nodal displacements. For pyramidal truss we determined a function of force in dependence of vertical displacement of uniaxial structural elements for different starting angles at which the uniaxial structural elements were clamped. Accuracy of analytical solution for snap-through system, which we got for different starting angles of uniaxial structural elements, was verified on experimental results obtained in the laboratory.
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ABSTRACT The bending behaviour of thin-walled profiles made from high-strength steels with respect to a changing angle of the bending plane or, in other words, the rotation of the section geometry on the longitudinal axis of the profile,... more
ABSTRACT The bending behaviour of thin-walled profiles made from high-strength steels with respect to a changing angle of the bending plane or, in other words, the rotation of the section geometry on the longitudinal axis of the profile, has not yet been fully characterized. The investigations presented in this paper lead to an improvement of the description for bending square hollow sections under unified and constant loading conditions, and contribute to the general understanding of such bending problems. The methodological approach is based on analytic, numerical, and experimental analysis. The analytical formulation is primarily built on the principle of a simplified cantilever beam model. Bending curvatures are assumed to be generated with constant radiuses of curvatures. The change of the angle of the section, with respect to the direction of bending, is applied before bending and remains unchanged throughout the process. In this way, the effects of a changing angle with regard to the direction of bending are analyzed for several constant curvatures and angles of 2D bent profiles. With a clear understanding of the 2D bending of high strength profiles, the same principles can also be used incrementally for analyses of 3D bending. The analytical theory is tested with an emphasis on using profiles with high-strength material properties compared to profiles made from standard low-carbon steel, by using the innovative torque superposed spatial (TSS) bending method. The results are supported by FE models generated with the Abaqus numerical FEM tool and verified with the results of actual experiments.
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ABSTRACT A digital image could be used as a source of data for various dimensional measurements. After acquiring the digital image of the measured object, the object contour is determined. The contour is composed of a sequence of distinct... more
ABSTRACT A digital image could be used as a source of data for various dimensional measurements. After acquiring the digital image of the measured object, the object contour is determined. The contour is composed of a sequence of distinct pixels which contain centre points. This is a representation of a digital curve or digital arc from which the object length or the perimeter could be determined. In order to calculate the approximate length of the object, we introduce a new algorithm called an anchored discrete convolution. The algorithm is based on a discrete convolution by using different convolution masks and points anchored in the pixels. Unfortunately, the use of an ordinary convolution distorts the curve shape and introduces large errors in length calculation. In our case the anchoring limits the point shifting into the pixel area during the calculation of the curve length. In this paper different convolution masks are used on an experimental digital curve in order to evaluate the presented algorithm as a measuring tool. In addition, different real objects were optically scanned and the perimeters of the objects were determined from the acquired images. Keywords: anchored discrete convolution, digital image, length measurement.
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This article investigates a method for obtaining all equilibrium configurations of a cantilever beam subjected to an end load with a constant angle of inclination. The formulation is based on plane finite-strain beam theory in the elastic... more
This article investigates a method for obtaining all equilibrium configurations of a cantilever beam subjected to an end load with a constant angle of inclination. The formulation is based on plane finite-strain beam theory in the elastic domain. An example of a cantilever beam subjected to a horizontal pressure force is discussed in detail.
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The paper deals with stresses, strains and buckling conditions in the thin axi-symmetric shallow bimetallic shells with circular opening at the top of the shell. According to the third order theory by the Czech researcher E. Chawalla,... more
The paper deals with stresses, strains and buckling conditions in the thin axi-symmetric shallow bimetallic shells with circular opening at the top of the shell. According to the third order theory by the Czech researcher E. Chawalla, which takes into account the equilibrium state of forces and moments acting on the deformed system, the paper presents a model for mathematical
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Purpose: Phenomena of deformation and fracture of two-phase metal matrix materials are two very interesting problems in the sceintific field of materials science and engineering. The study of these two issues can greatly contribute to... more
Purpose: Phenomena of deformation and fracture of two-phase metal matrix materials are two very interesting problems in the sceintific field of materials science and engineering. The study of these two issues can greatly contribute to better mechanical and technological properties of two-phase metal matrix materials. Design/methodology/approach: This work presents macroscopic models of two-phase metal matrix material, composed of ductile matrix and more rigid and hard inclusions (inserts) of secondary phase, prepared for the tensile deformation. These types of models are enlarged for two to three orders of magnitude comparing to the real copper matrix materials, and they are suitable for numerical as well as experimental modelling and simulation. Findings: The basic aim of the numerical and experimental modelling is in the observation of the matrix material flow, and in analysis of the stress-strain state in the matrix. Research limitations/implications: Deficiencies in FEA of the t...
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This article investigates a method for obtaining all equilibrium configurations of a cantilever beam subjected to an end load with a constant angle of inclination. The formulation is based on plane finite-strain beam theory in the elastic... more
This article investigates a method for obtaining all equilibrium configurations of a cantilever beam subjected to an end load with a constant angle of inclination. The formulation is based on plane finite-strain beam theory in the elastic domain. An example of a cantilever beam subjected to a horizontal pressure force is discussed in detail.
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ABSTRACT In this contribution, we discuss the stress, deformation, and snap-through conditions of thin, axi-symmetric, shallow bimetallic shells of so-called parabolic-conic and plate-parabolic type shells loaded by thermal loading.... more
ABSTRACT In this contribution, we discuss the stress, deformation, and snap-through conditions of thin, axi-symmetric, shallow bimetallic shells of so-called parabolic-conic and plate-parabolic type shells loaded by thermal loading. According to the theory of the third order that takes into account the balance of forces on a deformed body, we present a model with a mathematical description of the system geometry, displacements, stress, and thermoelastic deformations. The equations are based on the large displacements theory. We numerically calculate the deformation curve and the snap-through temperature using the fourth-order Runge-Kutta method and a nonlinear shooting method. We show how the temperature of both snap-through depends on the point where one type of the rotational curve transforms into another.
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