Zielinski T.G.,Polish Institute of Fundamental Technological Research
Journal of Vibration and Acoustics, Transactions of the ASME | Year: 2010
This paper presents a fully coupled multiphysics modeling and experimental validation of the problem of active reduction of noise generated by a thin plate under forced vibration. The plate is excited in order to generate a significant low-frequency noise, which is then reduced by actuators in the form of piezoelectric patches glued to the plate with epoxy resin in locations singled out earlier during finite element (FE) analyses. To this end, a fully coupled FE system relevant for the problem is derived. The modeling is very accurate: The piezoelectric patches are modeled according to the electromechanical theory of piezoelectricity, the layers of epoxy resin are thoroughly considered, and the acoustic-structure interaction involves modeling of a surrounding sphere of air with the nonreflective boundary conditions applied in order to simulate the conditions found in anechoic chamber. The FE simulation is compared with many experimental results. The sound pressure levels computed in points at different distances from the plate agree excellently with the noise measured in these points. Similarly, the computed voltage amplitudes of controlling signal turn out to be very good estimations. © 2010 American Society of Mechanical Engineers.
Hoffman J.,Polish Institute of Fundamental Technological Research
Journal of Physics D: Applied Physics | Year: 2015
Our experiments with the ablation of graphite by a nanosecond laser pulse showed the formation of craters with a depth of upto 60 μm. The creation of such deep craters is hard to explain solely by evaporation. Existing models should be supplemented by an additional mass removal process that ensures penetration of the material. The recoil pressure at the surface of the target generates a compression wave propagating deep into the material. Possible mechanisms of fracture by the longitudinal compression wave are discussed. A phenomenological model of material fragmentation is proposed. Modelling results are in good agreement with the experiment. The model may be used for polycrystalline graphite as well as other brittle materials treated by the nanosecond laser pulse. © 2015 IOP Publishing Ltd.
Kucharski S.,Polish Institute of Fundamental Technological Research |
Starzynski G.,Polish Institute of Fundamental Technological Research
Wear | Year: 2014
In the paper a problem of contact of rough surface with rigid flat plane is investigated experimentally and numerically. Samples made of three different steels with roughness constituted in a sand-blasting process were compressed in a special experimental setup. 3D surface topographies were measured in initial and deformed state using scanning profilometry. An experimental procedure has been designed that enables specifying load-approach and load-real contact area relations corresponding to plastic deformation of roughness zone. These relations were also simulated using a simple model based on statistical approach with special procedure proposed for a proper specification of sampling interval. The experimental and numerical results have been compared. © 2014 Elsevier B.V.
Jarzabek D.M.,Polish Institute of Fundamental Technological Research
Review of Scientific Instruments | Year: 2015
A direct method for the evaluation of the torsional spring constants of the atomic force microscope cantilevers is presented in this paper. The method uses a nanoindenter to apply forces at the long axis of the cantilever and in the certain distance from it. The torque vs torsion relation is then evaluated by the comparison of the results of the indentations experiments at different positions on the cantilever. Next, this relation is used for the precise determination of the torsional spring constant of the cantilever. The statistical analysis shows that the standard deviation of the calibration measurements is equal to approximately 1%. Furthermore, a simple method for calibration of the photodetector's lateral response is proposed. The overall procedure of the lateral calibration constant determination has the accuracy approximately equal to 10%. © 2014 AIP Publishing LLC.
Kursa M.,The Interdisciplinary Center |
Bajer K.,University of Warsaw |
Lipniacki T.,Polish Institute of Fundamental Technological Research
Physical Review B - Condensed Matter and Materials Physics | Year: 2011
We demonstrate that a single reconnection of two quantum vortices can lead to the creation of a cascade of vortex rings. Our analysis involves localized induction approximation, high-resolution Biot-Savart and Gross-Pitaevskii simulations. The latter showed that the rings cascade starts on the atomic scale, with rings diameters orders of magnitude smaller than the characteristic line spacing in the tangle. Vortex rings created in the cascades may penetrate the tangle and annihilate on the boundaries. This provides an efficient decay mechanism for sparse or moderately dense vortex tangle at very low temperatures. © 2011 American Physical Society.
Pieczyska E.A.,Polish Institute of Fundamental Technological Research
Meccanica | Year: 2014
In this paper, an experimental study of thermomechanical coupling related to pseudoelastic deformation of ferromagnetic shape memory alloy (FSMA) is presented. NiFeGaCo single crystal was subjected to subsequent loading–unloading compression cycles. The stress–strain parameters were recorded by mechanical and laser extensometers. Fast and sensitive infrared camera was used in order to record infrared radiation emitted by the sample surface during the deformation process and to calculate temperature changes related to both exothermic forward and endothermic reverse martensitic transformations. Thanks to the applied techniques, we could investigate a nucleation and development of the stress-induced martensitic transformation. The obtained thermograms exposure localized character of the transformation, initiating in form of inclined bands of higher temperature and developing throughout the sample. The elaborated average temperature change of the SMA sample surface reflects an instantaneous rate of the transformation development. High repeatability of both mechanical and temperature changes obtained in the subsequent loading cycles indicates good thermomechanical properties of the FSMA crystal and confirms high accuracy of the measurement. © 2014, The Author(s).
Lengiewicz J.,Polish Institute of Fundamental Technological Research |
Stupkiewicz S.,Polish Institute of Fundamental Technological Research
Wear | Year: 2013
A computationally efficient model of evolution of contact and wear is developed for a general periodic pin-on-flat problem with the focus on the pin-on-disc configuration and Archard wear model. The evolving contact state is assumed to be fully controlled by the wear process except during a short initial transient period controlled by both wear and elasticity. The contact pressure distribution is thus obtained by considering only the local wear model and the geometry of the conforming contact, without referring to the underlying elasticity problem. Evolution of the contact state is then obtained by time integration of the resulting rate-problem, and two computational schemes are developed for that purpose employing either the forward- or the backward-Euler method. The model is successfully verified against a three-dimensional finite element model. A dimensionless wear-mode index specifying the relative magnitude of wear coefficients of the contact pair is introduced, and model predictions are presented as a function of this parameter. © 2013 Elsevier B.V.
Stupkiewicz S.,Polish Institute of Fundamental Technological Research
Computer Methods in Applied Mechanics and Engineering | Year: 2013
A fully coupled implicit scheme is developed for quasi-steady-state wear problems. The formulation admits finite configuration changes due to both deformation and wear. The unconditionally stable implicit backward-Euler scheme is used for time integration of the shape evolution problem. Thus, the solution may proceed with large time increments, contrary to the commonly used explicit forward-Euler scheme, in which the time increment is restricted by the stability condition. This comes at the cost that the shape transformation mapping constitutes an additional unknown. As a result, a kind of an arbitrary Lagrangian-Eulerian (ALE) formulation is obtained in which the problem is solved simultaneously for the nodal positions and displacements. The incremental coupled problem is solved using the Newton method which leads to a highly efficient computational scheme, as illustrated by two- and three-dimensional numerical examples. © 2013 Elsevier B.V.
Kowalczyk-Gajewska K.,Polish Institute of Fundamental Technological Research
International Journal of Solids and Structures | Year: 2012
In the paper the theoretical analysis of bounds and self-consistent estimates of overall properties of linear random polycrystals composed of arbitrarily anisotropic grains is presented. In the study two invariant decompositions of Hooke's tensors are used. The applied method enables derivation of novel expressions for estimates of the bulk and shear moduli, which depend on invariants of local stiffness tensor. With use of these expressions the materials are considered for which at the local level constraints are imposed on deformation or some stresses are unsustained. © 2012 Elsevier Ltd. All rights reserved.
Paczelt I.,University of Miskolc |
Mroz Z.,Polish Institute of Fundamental Technological Research
Computer Methods in Applied Mechanics and Engineering | Year: 2012
The relative sliding motion of two elastic bodies in contact under compressive tractions induces wear process and contact shape evolution. The transient process tends to a steady state at fixed contact stress and strain distribution. This state was assumed to correspond to the minimum of the wear dissipation power. The stationary condition of the response functional then provides the contact pressure distribution. The present paper is aimed at extending to results of previous analyses . [1-5] of steady state conditions to cases of periodic sliding of contacting bodies, assuming the existence of cyclic steady state conditions. The wear dissipation in the steady cyclic period is then minimized with respect to the contact pressure distribution. The solutions of several cases of wear processes induced by translational and rotational sliding illustrate the applicability of the proposed variational method. © 2012 Elsevier B.V.