1. |
Gałęzia A.♦, Orłowska-Gałęzia A., Application of Teager–Kaiser’s instantaneous frequency for detection of delamination in FRP composite materials,
Materials, ISSN: 1996-1944, DOI: 10.3390/ma14051154, Vol.14, No.5, pp.1154-1-24, 2021 Streszczenie: Composite materials are widely used in many engineering applications and fields of technology. One of the main defects, which occur in fiber-reinforced composite materials, is delamination. It manifests itself in the separation of layers of material and the damaged structure once subjected to mechanical loads degrades further. Delamination results in lower stiffness and the decrease of structure’s carry load capability. Its early detection is one of the tasks of non-invasive structural health monitoring of layered composite materials. This publication discusses a new method for delamination detection in fiber-reinforced composite materials. The approach is based on analysis of energy signal, calculated with Teager–Kaiser energy operator, and comparison of change of the weighted instantaneous frequency for measurement points located in- and outside of delamination area. First, applicability of the developed method was tested using simple models of vibration signals, reflecting considered phenomena. Next, the authors’ weighted instantaneous frequency was applied for detection of deamination using signals obtained from FEM simulated response of the cantilever beam. Finally, the methods effectiveness were tested involving real experimental signals collected by the laser Doppler vibrometer (LVD) sensor measuring vibrations of the delaminated glass-epoxy specimens. Słowa kluczowe: delamination, Teager–Kaiser energy operator, instantaneous frequency, fiber-reinforced composite material Afiliacje autorów:
Gałęzia A. | - | Warsaw University of Technology (PL) | Orłowska-Gałęzia A. | - | IPPT PAN |
|  | 140p. |
2. |
Orłowska A., Gałęzia A.♦, Świercz A., Jankowski Ł., Mitigation of vibrations in sandwich-type structures by a controllable constrained layer,
JOURNAL OF VIBRATION AND CONTROL, ISSN: 1077-5463, DOI: 10.1177/1077546320946130, pp.1-11, 2020 Streszczenie: This study presents and tests a method for semi-active control of vibrations in sandwich-type beam structures. This method adapts a strategy called prestress accumulation release. The prestress accumulation release strategy is based on structural reconfiguration: it uses short time, impulsive and localised changes of actuator properties (such as stiffness or damping), which are applied to a part of the system in the moments, when its strain energy attains a local maximum. The method has been earlier applied as a global control scheme to mitigate the fundamental vibration mode of a cantilever beam (by stiffness control) and in the task of mitigating the first four modes of a frame structure (by damping control). This study proposes a prestress accumulation release strategy and tests its effectiveness for the case of a three-layered sandwich structure, with the internal layer fabricated from a material with dissipative characteristic locally controllable through the material damping coefficient. In contrast to the earlier research, the control is applied thus at the level of material characteristics instead of a discrete set of dedicated actuators. Based on the finite element method, a numerical experiment involving a passively damped, as well as prestress accumulation release-controlled, three-layered cantilever beam excited by initial displacements was performed. The effectiveness of the approach was studied for a broad range of internal layer damping parameters. The presented results revealed a high potential of the prestress accumulation release strategy in semi-active damping of vibrations of sandwich-type structures. Słowa kluczowe: vibration control, sandwich structure, semi-active control, decentralised control, smart structures, constrained layer method Afiliacje autorów:
Orłowska A. | - | IPPT PAN | Gałęzia A. | - | Warsaw University of Technology (PL) | Świercz A. | - | IPPT PAN | Jankowski Ł. | - | IPPT PAN |
|  | 70p. |
3. |
Popławski B., Mikułowski G., Orłowska A., Jankowski Ł., On/off nodal reconfiguration for global structural control of smart 2D frames,
Journal of Applied and Computational Mechanics, ISSN: 2383-4536, DOI: 10.22055/jacm.2020.32454.2016, pp.1-9, 2020 Streszczenie: This paper proposes an on/off semi-active control approach for mitigation of free structural vibrations, designed for application in 2D smart frame structures. The approach is rooted in the Prestress-Accumulation Release (PAR) control strategies. The feedback signal is the global strain energy of the structure, or its approximation in the experimental setup. The actuators take the form of on/off nodes with a controllable ability to transfer moments (blockable hinges). Effectiveness of the approach is confirmed in a numerical simulation, as well as using a laboratory experimental test stand. Słowa kluczowe: structural reconfiguration, structural control, semi-active control, frame structures, controllable nodes Afiliacje autorów:
Popławski B. | - | IPPT PAN | Mikułowski G. | - | IPPT PAN | Orłowska A. | - | IPPT PAN | Jankowski Ł. | - | IPPT PAN |
|  | 20p. |
4. |
Orłowska A., Graczykowski C., Gałęzia A.♦, The effect of prestress force magnitude on the natural bending frequencies of the eccentrically prestressed glass fibre reinforced polymer composite beams,
Journal of Composite Materials, ISSN: 0021-9983, DOI: 10.1177/0021998317740202, Vol.52, No.15, pp.1-14, 2018 Streszczenie: This paper studies the effect of prestress force magnitude on natural frequencies and dynamic behaviour of eccentrically prestressed glass fibre reinforced polymer composite beams, including the theoretical background, numerical results and experimental verification. The term prestress indicates the initial tensile stress applied to the fibres embedded in selected external layers of the composite material. First, the paper presents the theoretical background of the finite element method modelling of prestressed composites. Then, the results of numerical simulations conducted for a five-layered glass-epoxy composite beam are presented. The natural frequencies corresponding to three initial bending modes are analyzed for different prestressing force levels and for different fibre volume content. Finally, the results are verificated by experimental modal analysis conducted on three different glass-epoxy composite specimens of various mechanical parameters. Both the numerical results obtained from finite element method and the experimental results obtained from experimental modal analysis reveal that the first bending frequency increases and the two subsequent bending frequencies decrease due to the prestressing force. The comparison of numerical and experimental data confirms the effect and allows to quantify the influence that the prestress force has on the natural frequencies of composites, which is an interesting and practically relevant phenomenon. Słowa kluczowe: Prestressed structures, laminated composites, prestressed reinforced composites, glass fibre reinforced polymer composite materials, vibrations, finite element method Afiliacje autorów:
Orłowska A. | - | IPPT PAN | Graczykowski C. | - | IPPT PAN | Gałęzia A. | - | Warsaw University of Technology (PL) |
|  | 30p. |
5. |
Graczykowski C., Orłowska A., Holnicki-Szulc J., Prestressed composite structures – Modeling, manufacturing, design,
COMPOSITE STRUCTURES, ISSN: 0263-8223, DOI: 10.1016/j.compstruct.2016.02.085, Vol.151, pp.172-182, 2016 Streszczenie: This paper presents a preliminary research aimed at developing a comprehensive approach to modeling, manufacturing and optimal design of prestressed FRP composite structures. A simple and effective analytical model of prestressed composite is derived and further verified by two numerical models and the results of the experimental tests conducted on manufactured prestressed composite samples. The model reveals beneficial influence of prestress on strain and stress distribution in particular plies and resulting improvement of the global response of the composite. A design case-study of prestressed composite is presented and challenges related to design and application of more complicated composite prestressed structures are discussed. Słowa kluczowe: Prestressed structures, Laminated composites, Prestressed FRP reinforced composites Afiliacje autorów:
Graczykowski C. | - | IPPT PAN | Orłowska A. | - | IPPT PAN | Holnicki-Szulc J. | - | IPPT PAN |
|  | 35p. |
6. |
Orłowska A., Kołakowski P., Holnicki-Szulc J., Detecting delamination zones in composites by embedded electrical grid and thermographic methods,
SMART MATERIALS AND STRUCTURES, ISSN: 0964-1726, DOI: 10.1088/0964-1726/20/10/105009, Vol.20, No.10, pp.105009-1-9, 2011 Streszczenie: The proposed approach assumes that the composite structure is equipped with a specially designed electrical circuit with a 3D grid layout, composed of high resistivity elements embedded in the structure. The special layout of the electrical circuit activated by small currents provides scattered sources of thermal field in the laminate. It is assumed that the circuit elements exhibit failure which is coincident with the commencement of delamination. These breaks in the electrical circuit cause variations in the thermal field which can be observed by a long-wave thermovision camera. The paper is focused on two research aspects. First, some numerical simulations are presented to examine the potential of the idea itself. Next, a simple experiment using a composite sample with a hand-fabricated electrical grid is described. The performance of the grid for an arbitrarily selected position of defect in the investigated composite shows high potential for damage detection. Afiliacje autorów:
Orłowska A. | - | IPPT PAN | Kołakowski P. | - | IPPT PAN | Holnicki-Szulc J. | - | IPPT PAN |
|  | 35p. |
7. |
Mróz A., Orłowska A., Holnicki-Szulc J., Semi-active damping of vibrations. Prestress Accumulation-Release strategy development,
SHOCK AND VIBRATION, ISSN: 1070-9622, DOI: 10.3233/SAV-2010-0502, Vol.17, pp.123-136, 2010 Streszczenie: New method for semi-active control of vibrating structures is introduced. So-called Prestress Accumulation-Release (PAR) strategy aims at releasing of the strain energy accumulated in the structure during its deformation process. The strain energy is converted into kinetic energy of higher modes of vibration which is suppressed with structural damping or by means of a damping device. The adaptation process essentially affects the first mode vibrations by introducing an elastic force that opposes the movement. Numerical simulations as well as experimental results prove that the strategy can be very effective in mitigating of the fundamental mode of a free – vibrating structure. In a numerical example 95% of the vibration amplitude was mitigated after two cycles. An experimental demonstrator shows 85% reduction of the amplitude in a cantilever free- vibrations. In much more complex practical problems smaller portion of total energy can be released from the system in each cycle, nevertheless the strategy could be applied to mitigate the vibrations of, for example, pipeline systems or pedestrian walkways. Afiliacje autorów:
Mróz A. | - | IPPT PAN | Orłowska A. | - | IPPT PAN | Holnicki-Szulc J. | - | IPPT PAN |
|  | 20p. |
8. |
Orłowska A., Kołakowski P., Holnicki-Szulc J., Modelling and identification of delamination in double-layer beams by the virtual distortion method,
COMPUTERS AND STRUCTURES, ISSN: 0045-7949, DOI: 10.1016/j.compstruc.2008.05.008, Vol.86, pp.2203-2214, 2008 Streszczenie: The problem of modelling and identification of delamination in double-layer beams has been undertaken within the framework of the virtual distortion method. For delamination modelling, a concept of the contact layer has been proposed, assuming simple but effective truss connections. The laminate layers have been modelled with Bernoulli beams. Good correspondence of the delamination model with experiments has been observed despite disregarding the friction between layers. An algorithm for off-line identification of delamination, solving an inverse problem with the use of gradient optimization, has been proposed. For double cantilever beam examples, two co-existing delamination zones have been successfully detected. An idea of on-line identification of delamination has been put forward, too. Słowa kluczowe: Delamination, Double-layer beams, Identification, Inverse problem Afiliacje autorów:
Orłowska A. | - | IPPT PAN | Kołakowski P. | - | IPPT PAN | Holnicki-Szulc J. | - | IPPT PAN |
|  |