Now showing 1 - 6 of 6
  • Publication
    Determination constants of 4-element reological model with rebound resilience method
    (2017) ;
    Svetlana Polukoshko
    ;
    Elvijs Apeinans
    ;
    In this paper an express-method and equipment for experimental determination of the 4-element rheological model constants (2 elastic modulus, 2 viscosity coefficients) for elastomers are developed. The method is based on rebound of falling hammer against an elastomer material. A mathematical model for describing this collision is elaborated and an algorithm for determination of the constants of the model was developed and realized in Matlab software. Time necessary for determination of the constants is until 5 minutes. It gives an opportunity to significantly accelerate the design and production process of elastomer-metal vibration isolator prototypes with defined parameters of stiffness and damping. The method allows to trace displacement, velocity and acceleration of the metal parts of the shock absorber throughout the collision; this may be realized with Matlab or an analogical program of numerical integration. For forecasting of the mechanical properties of the shock absorber during a long period (considering the aging of elastomer) it is necessary to know the rheological model parameter dependence on time, temperature, energy input and other factors; the proposed method allows to significantly accelerate these experimental studies.
    Scopus© Citations 2
  • Publication
    Laser hardening process optimization using FEM
    In given work a method for optimization of the process of laser hardening of steel parts is developed. The approach is based on the finite element method (FEM) using computer program “COMSOL Multiphysics” (module Heat Transfer in Solids) – software for multi-physical processes simulation. This method allows to reduce the number of laser hardening experiments, replacing them with numerical calculations, and to find the optimal parameters of the used laser equipment. To perform the calculations it is necessary to know the hardening temperature range of the particular steel grade, the martensite formation start temperature, the critical value of the cooling rate, the material density, the thermal conductivity k = k(T), the specific heat capacity Cp = Cp(T) and the surface reflectivity R = R(T, λ), where T temperature, λ – wavelength of laser beam. Depending on the laser power, the feed rates of the laser beam, the spot size and the distribution of energy in it, the temperature field is calculated for the steel part in different moments of time. Analysing these data it is possible to determine the thickness of the hardened layer or to predict damage to the material of a given steel part due to heat treatment. The method has been tested experimentally.
  • Publication
    Specifics of behavior and calculation of elastomeric shock absorber under impact loading
    (2018)
    Svetlana Polukoshko
    ;
    ;
    Vladimirs Gonca
    In this paper the important for the design of shock-absorbers case of a perfectly rigid body impact with a viscoelastic incompressible body is considered. Mathematical apparatus for calculating the parameters of impact of a rigid body with a highly- elastic rod is developed, taking into account the peculiarities of the behavior of elastomers under fast loading. An analytical solution was obtained for longitudinal impact on a vertically disposed rod. The solution was fulfilled by means of the Bubnov- Galerkin variational method, reducing the problem to solving of the integro-differential equation for given boundary and initial conditions The solution is received for the exponential relaxation kernel for the Maxwell model of a highly-elastic material, it describes the process of damped longitudinal vibration, taking into account the effect of creep caused by the instantaneous impact loading. Based on the equation of vibratory motion the equations of velocity and acceleration are received, which are used for stress-strain behavior analysis of rubber damper. A numerical example of an axial tensile impact on a viscoelastic shock-absorber in the form of a cylindrical rod is given with the plots of time dependence of displacement, velocity, and acceleration of the impact end of the rod are provided, the possibility of using them for analyzing the shock absorber is demonstrated.
    Scopus© Citations 1
  • Publication
    Air ionizer and indoor plants interaction impact on ion concentration
    (2017)
    Natalija Siņicina
    ;
    The plants emit different types of volatile organic compounds (Bio VOC’s) and can improve air quality: they effectively remove organic pollutions and reduce the number of microorganisms in the air by releasing phytoncides. The lack of negative ions in the air can cause deterioration of the health of humans breathing it. At the same time, an air saturated with negative ions can improve the state of health and provide a comfortable environment. In this article, the influence of the plants (Cupressus macrocarpa) on the number of ions is proved, based on a series of experiments performed with applying high-voltage pulses (air ionizer). This work is devoted to the elaboration of the mathematical relationship between the air ions concentration and the factors influencing it. For this purpose an experimental stand was made, consisting of two equal compartments: one contained the plants while another one was used as a control without plants. It was concluded that the plants, in general, are able to stabilize the ion concentration and to reduce its fluctuations. The plants help to increase the concentration of negative ions and to decrease the concentration of positive ones.
  • Publication
    Estimation of stress and displacement increase caused by heat generation in rubber vibration absorber
    (2020)
    Svetlana Polukoshko
    ;
    ;
    Vladimirs Gonca
    Rubber and rubber-like materials (elastomers) are widely used for anti-vibration mounts and shock absorbers for vehicles, machinery, building structures due to their specific properties: ability to absorb vibration and shock loads, low elastic modulus, high mechanical strength, high elongation at brake, reversible elastic deformation. Rubber is a material that is capable of recovering from large deformations quickly and forcibly, which is suitable for work under cyclic loading. During deformation elastomeric materials absorb in an irreversible way part of the energy, causing this deformation. The energy absorbed during each cycle heats the deformed rubber element and dissipates in media. Heat generation in rubber causes additional stresses and deformations which are poorly known, and they are a subject of our study. In the presented paper the work of a rubber anti-vibration mount in the form of a straight circular cylinder under action of cyclic loading is studied. Poisson’s ratio of the rubber material is μ = 0.5, the weight of the mount is not taken into account. Temperature field is assumed known based on the previous work (it depends on the frequency and amplitude of vibration, heat conductivity and heat capacity of the material, etc.). The stress-strain state analysis was carried out based on the Reissner variational principle. Analytical dependences for temperature additions to stresses and displacements are derived that allows estimating stiffness of the anti-vibration mount and its increase as a result of self-heating. Obtained results may be useful for proper design of anti-vibration mounts allowing changing geometrical dimensions in order to reach the required temperature field.
  • Publication
    Torsional, compression and shear stiffness of thin-layer rubber-metal spherical joint-hinge
    (2017)
    Svetlana Polukoshko
    ;
    ;
    Vladimirs Gonca
    In this paper laminated elastomeric bearings (composite of thin elastomer and metal layers) are considered. This type of bearings or joint-hinge has many advantages because of ease of maintenance; ability to work in a very aggressive environment, low cost and vibration damping capability. The geometric shape of such bearing may be planar, cylindrical, conical, spherical and other, given work deals with spherical thin-layered rubber-metal bearings. Operating of such device depends on many factors that must be considered on the design stage: parameters of the elements must be selected properly. The most important parameter is stiffness – dependence between imposed force and received deformation. In this work torsional, compression and shear stiffness of laminated bearings was defined for the testing specimens by experiments and torsional stiffness was received analytically. Both methods show good enough coincidence.