bohdana marvalova
Technical University of Liberec, Department of Applied Mechanics, Department Member
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The tensile and bending properties of composite materials with geopolymer matrix reinforced by layers of basalt plain weave fabric were investigated experimentally. We present the results of the quasi-static tensile tests and the... more
The tensile and bending properties of composite materials with geopolymer matrix reinforced by layers of basalt plain weave fabric were investigated experimentally. We present the results of the quasi-static tensile tests and the quasi-static and cyclic three-point bending tests. The composite panels were made by hand laying with subsequent vacuuming. The plates were stayed in a compression press and left in a compressed state for a month. After 5 months the samples were made from the plates and subjected to tests. The material behaves as linear almost to the failure, which occurred at tensions of about 100 MPa. The elastic modulus is between 6000 and 7000 MPa.
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Experimental research and numerical computation of stress relaxation behavior of an anisotropic magnetorheological elastomer (MRE) have been conducted in this paper. The anisotropic MRE has been fo...
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The paper presents the experimental and numerical research of dynamic mechanical properties of magneto-sensitive elastomeric composites (MECs). The isotropic and anisotropic MEC samples are produced from silicone matrix filled by... more
The paper presents the experimental and numerical research of dynamic mechanical properties of magneto-sensitive elastomeric composites (MECs). The isotropic and anisotropic MEC samples are produced from silicone matrix filled by magnetically sensitive micro-sized carbonyl iron particles. Dynamic double-lap shear tests are conducted for both isotropic and anisotropic MEC specimens under various frequencies of loading and magnetic field intensities. The stiffness and damping properties of the MECs increased with increasing of the frequency and magnetic intensity. The dynamic properties of the anisotropic MECs were higher than those of the isotropic ones. The dependency of dynamic moduli on frequency and magnetic field is studied using the four-parameter fractional Zener model with fractional derivatives on stress and strain. The four-parameter fractional viscoelastic model was fitted quite well to experimental data for both isotropic and anisotropic MECs. The fitting of the storage and loss moduli for isotropic and anisotropic MECs is in good agreement with experimental results in the middle of investigated frequency band
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Self-heating and dynamic mechanical behavior of isotropic silicone rubber composite (SRC) filled with micro-sized carbonyl iron particles (CIPs) subjected to cyclic compressive loading have been studied. Effects of pre-strains from 5 to... more
Self-heating and dynamic mechanical behavior of isotropic silicone rubber composite (SRC) filled with micro-sized carbonyl iron particles (CIPs) subjected to cyclic compressive loading have been studied. Effects of pre-strains from 5 to 20%, strain amplitudes from 1 to 5%, and excitation frequencies from 10 to 50 Hz on the self-heating and dynamic mechanical response of the isotropic SRC were investigated. The self-heating temperatures were measured on the surface and at the center of cylindrical SRC specimens. The self-heating temperatures of the isotropic SRC samples showed a fast increase in an initial transient stage and the following isothermal stage. The temperature distribution in the isotropic SRC specimens was non-homogeneous and the temperature decreased from the center to sample edges. The self-heating temperatures of the isotropic SRC increased gradually with raising the strain amplitude and frequency. However, the difference between the internal and surface temperatures was slight for low strain amplitudes and frequencies, while it was significant for high strain amplitudes and frequencies. The temperatures of the isotropic SRC boosted rapidly with increasing the pre-strain to 10% and thereafter gained slightly. Although the isotropic SRC dynamic moduli reduced with the rise of the strain amplitude, they enhanced with increasing the pre-strain and frequency. Besides, the storage modulus of the isotropic SRC varied slightly with time, while the loss modulus reduced markedly especially at the initial period. The decrease in the loss modulus of the isotropic SRC under cyclic compressive loading is attributed to its self-heating temperature rise. A finite element simulation of the heat transfer in the SRC cylinder was conducted. The calculated temperatures in the SRC cylinder were in good agreement with the measured ones at different strain amplitudes and frequencies.
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Experimental study and numerical investigation of stress relaxation behavior of isotropic magnetorheological elastomeric composite (MEC) were carried out in this article. The isotropic MEC was produced from silicone rubber reinforced with... more
Experimental study and numerical investigation of stress relaxation behavior of isotropic magnetorheological elastomeric composite (MEC) were carried out in this article. The isotropic MEC was produced from silicone rubber reinforced with micro-sized carbonyl iron particles. The stress relaxation response of the isotropic MEC was investigated at different loading rates, constant strain levels, and under various electromagnetic fields through the single relaxation test with double-lap shear specimens. Research results indicated that the stress relaxation of the isotropic MEC depended slightly on the loading rate, but it was considerably dependent on the constant strain and the electromagnetic field. The shear stress and modulus of the MEC in the relaxation period enhanced with increasing the constant strain and electromagnetic field intensity as well. The stress relaxation of the isotropic MEC was examined numerically using the four-parameter fractional derivative viscoelastic Zener model. The studied fractional derivative viscoelastic model was fitted well to the measured relaxation modulus of the isotropic MEC. The calculated shear stresses of the isotropic MEC with long-term predictions agreed well with the measured ones. Therefore, the investigated fractional derivative viscoelastic model can apply to predict the long-term stress relaxation behavior of the isotropic MEC.
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This paper contains the project overview of complex research of conveyor belts affected especially by impact (shock) loading. The main task is to increase working life of conveyor belt based on optimization of size and shape of... more
This paper contains the project overview of complex research of conveyor belts affected especially by impact (shock) loading. The main task is to increase working life of conveyor belt based on optimization of size and shape of transported parts, dropping height, design of the belt and impact area. Project contains theoretical, experimental and numerical analyses. The best types of modifications will be realized in the surface mining company. Project is oriented especially to optimization of drive and return stations using of detailed numerical models, new design concepts and materials. Project also proves possibilities for size and shape monitoring of transported parts and active modification of geometry based on type of transported materials. T&L 1 INTRODUCTION This paper contains the research and development project overview of conveyor belts affected by shocks in brown coal surface mine. The project started on 3/2012 and finish is planned on 12/2014. This project is solved in co...
Nonlinear hyperelastic constitutive equations for large deformations of orthotropic composite material are incorporated into the finite strain analysis by FEM. The parameters of material are determined from experiments. Results for the... more
Nonlinear hyperelastic constitutive equations for large deformations of orthotropic composite material are incorporated into the finite strain analysis by FEM. The parameters of material are determined from experiments. Results for the deformation of the inflated air-spring shell made of composite with rubber matrix reinforced by textile cords are given.
MEASUREMENT OF FRICTION AND DAMPING PROPERTIES OF RUBBER MĚŘENÍ TŘECÍCH A ÚTLUMOVÝCH VLASTNOSTÍ PRYŽE Abstract Friction of rubber depends on different parameters e.g. velocity, roughness, normal pressure and temperature. The coefficient of friction is measured by ball-on-disc method at ambimore
Friction of rubber depends on different parameters e.g. velocity, roughness, normal pressure and temperature. The coefficient of friction is measured by ball-on-disc method at ambient temperature. The dependence of the coefficient on... more
Friction of rubber depends on different parameters e.g. velocity, roughness, normal pressure and temperature. The coefficient of friction is measured by ball-on-disc method at ambient temperature. The dependence of the coefficient on different sliding velocities and on different normal forces is observed. The coefficient of friction is compared with the rubber damping properties determined by dynamic mechanical analysis.
The 3-D displacements of inflated cylindrical shell of air-spring made of cord-rubber composite are measured by the application of the stereo-correlation technique. The 3-D coordinates of points in the central part of air-spring shell are... more
The 3-D displacements of inflated cylindrical shell of air-spring made of cord-rubber composite are measured by the application of the stereo-correlation technique. The 3-D coordinates of points in the central part of air-spring shell are obtained at different stages of loading by the matching of a series of stereo images. By the use of the nonlinear optimization technique, the deformations of the air-spring shell are determined. The material parameters of strain energy function are identified. The deformations of inflated air-spring shell were determined by numerical solution the system of ordinary differential equations based on the membrane theory.
In this paper we present an attempt to identify experimentally the coefficients of strain energy function of the hyperelastic orthotropic material of the thin cylindrical air-spring. The components of the deformation gradient are... more
In this paper we present an attempt to identify experimentally the coefficients of strain energy function of the hyperelastic orthotropic material of the thin cylindrical air-spring. The components of the deformation gradient are determined from measured displacements of the grid points drawn on the cylindrical surface of the spring. The true Cauchy stress tensor is calculated from the membrane theory. The deformed shape of the spring surface is determined from the photographic records. The strain energy function is expressed in terms of tensorial invariants with regard to the assumed material symmetry. The coefficients are determined by means of the nonlinear least squares method. The deformation field is then calculated by solving the system of five first-order ordinary differential equations with the material constitutive law and proper boundary conditions.
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Available from STL Prague, CZ / NTK - National Technical LibrarySIGLECZCzech Republi
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Magnetorheological elastomers (MREs) belong to the new group of functional materials called “smart”. The MR effect is increased by choosing the material of the particles with high permeability. The dependence of dynamic moduli and damping... more
Magnetorheological elastomers (MREs) belong to the new group of functional materials called “smart”. The MR effect is increased by choosing the material of the particles with high permeability. The dependence of dynamic moduli and damping of MREs on the external magnetic field and the applied frequency of cyclic shear deformation was studied. Samples of MRE were made of the silicon rubber matrix filled with micron-sized particles. The dynamic stiffness of MRE depends on magnetic flux density and rises with increasing frequency. The loss factor of MRE samples is controlled by the magnetic flux density and it depends also on the testing frequency. The behaviour of viscoelastic materials under uniaxial loading may be represented using rheological models composed of elastic and viscous elements. The dynamic variables storage and loss moduli and loss tangent were determined on the basis of the fitted parameters of the fractional model.
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Low velocity impact strength of the fabric reinforced geocomposite has investigated in this article. Various fabrics such as carbon and E-glass were considered for reinforcement in geopolymer matrix. The primary two parameters such as low... more
Low velocity impact strength of the fabric reinforced geocomposite has investigated in this article. Various fabrics such as carbon and E-glass were considered for reinforcement in geopolymer matrix. The primary two parameters such as low velocity, impact damage modes are explained on the E-glass and carbon based fabric geocomposite. The onset mode of damage to failure mode is examined through C-scan analysis. The quality of the composite is observed using c-scan with acoustic vibration mode of sensor before and after impact test. Then the effect of fabric and matrix on the impact behaviour is discussed. Residual strength of the composite is measured to determine post impact behaviour. It has been observed that resistance properties of E-glass reinforced composite is better than carbon fabric reinforced composite.
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Research Interests: Materials Science and CRC
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Biaxial tension test of the cruciform specimen of styrene-butadiene rubber is described in this paper. The rubber layer is a part of the conveyor belt used for the transportation of coal. The specimen are loaded by the home made biaxial... more
Biaxial tension test of the cruciform specimen of styrene-butadiene rubber is described in this paper. The rubber layer is a part of the conveyor belt used for the transportation of coal. The specimen are loaded by the home made biaxial testing device. The big deformation of specimen are determined by the Digital Image Correlation. The parameters of Mooney-Rivlin hyperelastic material were determined. Numerical simulation of the biaxial test was performed in Comsol Muliphysics.
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The paper describes a complex experimental research of tribological and mechanical properties of styrene-butadiene-rubber (SBR) filled with carbon black. Tribological properties of SBR rubber material are investigated experimentally using... more
The paper describes a complex experimental research of tribological and mechanical properties of styrene-butadiene-rubber (SBR) filled with carbon black. Tribological properties of SBR rubber material are investigated experimentally using a home made device of ball-on-disc type. The response of SBR in sliding friction depends on sliding speed and on the loading force. The rate-dependent behaviour of carbon-black filled rubber is investigated in tensile tests with different loading rates and in relaxation tests. The viscosity-induced rate-dependent effects are described. The storage and loss moduli and phase angle δ dependency on different amplitudes and frequencies are determined by strain controlled dynamical mechanical analysis. The temperature dependence of dynamic and tribological behaviour of SBR is also investigated.Copyright © 2010 by ASME
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ABSTRACT The evolution of the microstructures in Zr-based in-situ bulk metallic glass matrix composites was investigated by semi-solid processing and mechanical testing. A linear relationship between the cube root holding time and the... more
ABSTRACT The evolution of the microstructures in Zr-based in-situ bulk metallic glass matrix composites was investigated by semi-solid processing and mechanical testing. A linear relationship between the cube root holding time and the length scales of the precipitated β-Zr phase is established. Moreover, we have demonstrated that the mechanical properties of the composites are closely related to the length scales of the precipitated β-Zr phase. With the increase in the characteristic size scale, the plasticity of the BMG matrix composites is enhanced significantly. When the characteristic size scale of the β-Zr phase exceeds a critical value, this increasing trend becomes very moderate.
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The paper presents an implementation in Comsol Multiphysics 3.3 of Holzapfel's material model for the viscoelastic stress response of carbon-black filled rubber at large strains. The finite strain formulation is based on the material... more
The paper presents an implementation in Comsol Multiphysics 3.3 of Holzapfel's material model for the viscoelastic stress response of carbon-black filled rubber at large strains. The finite strain formulation is based on the material configuration with the right Cauchy-Green tensor as a strain measure. The time independent response of the rubber is modelled by the Mooney-Rivlin hyperelastic material with uncoupled