Makine Mühendisliği Bölümü Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.11779/1944
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Article Citation - WoS: 6Citation - Scopus: 7A New Approach for Measuring Viscoelastic Properties of Soft Materials Using the Dynamic Response of a Spherical Object Placed at the Sample Interface(Springer, 2023) Besli, Ayça; Körük, Hasan; Körük,Hasan; Yurdaer, Berk Salih; Koc, H. O.; Yurdaer, S. B.; Pouliopoulos, A. N.; 02.03. Department of Mechanical Engineering; 02. Faculty of Engineering; 01. MEF UniversityBackground: There are several techniques to characterize the mechanical properties of soft materials, such as the indentation method and the method based on the application of a spherical object placed inside the sample. The indentation systems usually yield the elastic properties of materials and their mathematical models do not consider the inertia of the sample involved in motion and radiation damping, while placing an object inside the sample is not practical and this procedure can alter the mechanical properties of the sample for the method based on the application of a bubble/sphere placed inside the sample. Objective: A new approach for the identification of the viscoelastic properties of soft materials using the dynamic response of a spherical object placed at the sample interface was proposed. Methods: The spherical object placed at the sample interface was pressed using an electromagnet and the dynamic response of the spherical object was tracked using a high-speed camera, while the dynamic response of the spherical object placed at the sample interface was estimated using a comprehensive analytical model. The effects of the shear modulus, viscosity, Poisson’s ratio and density of the soft sample, the radius and density of the spherical object and the damping due to radiation were considered in this mathematical model. The shear modulus and viscosity of the soft sample were determined by matching the experimentally identified and theoretically estimated responses of the spherical object. Results: The shear moduli and viscosities of the three phantoms with the gelatin mass ratios of 0.20, 0.25 and 0.29 were measured to be 3450, 4300 and 4950 Pa and 12.5, 14.0 and 15.0 Pa⋅s, respectively. The shear modulus and viscosity of the phantom increases as the gelatin mass ratio increases. The frequency of oscillations of the hemisphere placed at the phantom interface increases as the gelatin mass ratio increases due to stiffness increase. Conclusions: After matching the experimental and theoretical steady-state displacements and amplitudes of oscillations of the hemisphere at the sample interface, the comparison of the experimentally identified and theoretically predicted frequency of oscillations further confirmed the identified material properties of the samples. The approach presented here is expected to provide valuable information on material properties in biomedical and industrial applications.Article Biyomalzemelerin Akustik ve Mekanik Özelliklerinin Arastırılması(2020) Genç, Garip; Körük,Hasan; Körük, Hasan; 02.03. Department of Mechanical Engineering; 02. Faculty of Engineering; 01. MEF UniversityBu proje kapsamında, jüt lifleri ve çesitli luffa lifleri kullanılarak, farklı kalınlıklarda reçinesiz (hiçbir reçine kullanılmayan) homojen ve hibrit jüt ve luffa yapılar ve yine farklı kalınlıklarda ve farklı lif/reçine oranlarında reçineli homojen ve hibrit jüt ve luffa yapılar üretilerek, bu yapıların akustik ve mekanik özellikleri ile ilgili kapsamlı bir resmin ortaya konulması hedeflenmistir. Bu kapsamda kullanılan yöntemler/sonuçlar su sekildedir: (i) Akustik testler için farklı kalınlıklarda hem reçinesiz hem de farklı lif/reçine oranlarına sahip reçineli homojen ve hibrit numuneler üretilmistir. Empedans tüp yöntemi kullanılarak bu akustik numunelerin ses yutma ve ses iletim kaybı gibi akustik özellikleri deneysel olarak belirlenmistir. Homojen ve hibrit kompozit yapıların akustik performansları karsılastırılmıstır. Sonuçta, kalınlık ve lif/reçine oranın bu yapıların akustik özellikleri üzerindeki etkisi ortaya konulmustur. (ii) Farklı frekans aralıkları için kalınlıgın ve lif/reçine oranının bir fonksiyonu olarak ölçülen akustik verilere egriler uydurularak, malzemelerin akustik özelliklerini belirlemeye yönelik basit ampirik modeller ortaya konulmustur. Dahası, malzemelerin ses yutma katsayıları Delany-Bazley ve Johnson- Champoux-Allard gibi teorik modeller kullanılarak tahmin edilmis ve sonuçlar deneysel sonuçlarla karsılastırılmıstır. Benzer sekilde, numunelerin ses iletim kayıpları teorik olarak hesaplanmıs ve deneysel sonuçlarla karsılastırılmıstır. Sonuçta, bu yapıların tasarımında akustik amaçla kullanılabilecek ampirik ve teorik modeller ortaya konulmustur. (iii) Titresim testleri için farklı kalınlık ve lif/reçine oranlarına sahip reçineli homojen ve hibrit numuneler üretilmis, üretilen bu yapılar üzerinde akustik ve yapısal frekans tepki fonksiyonları ölçülmüs ve aynı yapıların teorik modellerinden yararlanılarak malzemelerin elastik ve sönüm gibi mekanik özellikleri belirlenmistir. Homojen jüt ve luffa kompozit yapıları hem izotropik varsayılarak hem de bu yapıların yöne baglı elastik özelliklerinin olması durumu dikkate alınarak modellenmislerdir. Sonuçta, kalınlık ve lif/reçine oranın mekanik özellikler üzerindeki etkisi ortaya konulmus ve pratikte bu yapıların tasarımı için kullanılabilecek bazı yaklasımlar ortaya konulmustur.Conference Object The Minimum Variance Distortionless Response Beamformer for Damage Identification Using Modal Curvatures(Association of American Publishers, 2023) Eroğlu, Uğurcan; Pau, A.; 01. MEF UniversityThis study presents a damage identification procedure in beams based on the use of beamforming algorithms, which are mostly utilized in inverse problems of source identification and image reconstruction. We choose the modal curvatures as observed quantities and compare the performance of the Bartlett beamformer, minimum variance distortionless response (MVDR) processor, and of a conventional objective function based on the modal curvatures. By means of a set of experiments, we show that the MVDR processor can overcome some of the difficulties encountered with other estimators, especially in cases of slight damage, or damage located between two sensors. © 2023, Association of American Publishers. All rights reserved.Conference Object Perturbations for Vibration of Nano-Beams of Local/Nonlocal Mixture(Association of American Publishers, 2023) Ruta, Giuseppe; Eroğlu, Uğurcan; 01. MEF UniversityHere we extend the perturbation approach, previously presented in the literature for Eringen’s two-phase local/nonlocal mixture model, to free vibration of purely flexible beams. In particular, we expand the eigenvalues and the eigenvectors into power series of the fraction coefficient of the non-local material response up to 2nd order. We show that the family of 0th order bending couples satisfy the natural and essential boundary conditions of the 1st order; hence, the 1st order solution can conveniently be constructed using the eigenspace of the 0th order with no necessity of additional conditions. We obtain the condition of solvability that provides the incremental eigenvalue in closed form. We further demonstrate that the 1st order increment of the eigenvalue is always negative, providing the well-known softening effect of long-range interactions among the material points of a continuum modelled with Eringen’s theory. We examine a simply supported beam as a benchmark problem and present the incremental eigenvalues in closed form. © 2023, Association of American Publishers. All rights reserved.Article Citation - WoS: 2Citation - Scopus: 2Approximate Closed-Form Solutions for Vibration of Nano-Beams of Local/Non-local Mixture(Springer, 2022) Ruta, Giuseppe; Eroğlu, Uğurcan; 01. MEF UniversityThis paper presents an approach to natural vibration of nano-beams by a linear elastic constitutive law based on a mixture of local and non-local contributions, the latter based on Eringen's model. A perturbation in terms of an evolution parameter lets incremental field equations be derived; another perturbation in terms of the non-local volume fraction yields the variation of the natural angular frequencies and modes with the 'small' amount of non-locality. The latter perturbation does not need to comply with the so-called constitutive boundary conditions, the physical interpretation of which is still debated. The possibility to find closed-form solutions is highlighted following a thorough discussion on the compatibility conditions needed to solve the steps of the perturbation hierarchy; some paradigmatic examples are presented and duly commented.Article Citation - WoS: 1Citation - Scopus: 1Acoustic Cavitation Model Based on a Novel Reduced Order Gas Pressure Law(AIP Publishing, 2021) Pasinlioğlu, Şenay; Delale, Canfuad; 02.03. Department of Mechanical Engineering; 02. Faculty of Engineering; 01. MEF UniversityThe thermal behavior of a spherical gas bubble in a liquid excited by an acoustic pressure signal is investigated by constructing an iterative solution of the energy balance equations between the gas bubble and the surrounding liquid in the uniform pressure approximation. This iterative solution leads to hierarchy equations for the radial partial derivatives of the temperature at the bubble wall, which control the temporal rate of change of the gas pressure and gas temperature within the bubble. In particular, a closure relation for the hierarchy equations is introduced based on the ansatz that approximates the rapid change of state during the collapse of the bubble from almost isothermal to almost adiabatic behavior by time averaging the complex dynamics of change of state over a relatively short characteristic time. This, in turn, leads to the desired reduced order gas pressure law exhibiting power law dependence on the bubble wall temperature and on the bubble radius, with the polytropic index depending on the isentropic exponent of the gas and on a parameter that is a function of the Péclet number and a characteristic time scale. Results of the linear theory for gas bubbles are recovered by identifying this parameter as a function of the Péclet number based on the Minnaert frequency. The novel gas pressure law is then validated against the near-isothermal solution and against the results of the numerical simulations of the original energy balance equations for large amplitude oscillations using spectral methods. Consequently, an acoustic cavitation model that accounts for phase change but that neglects mass diffusion is constructed by employing the reduced order gas pressure law together with the Plesset–Zwick solution for the bubble wall temperature and the Keller–Miksis equation for spherical bubble dynamics. Results obtained using variable interface properties for acoustically driven cavitation bubbles in water show that the time variations of the bubble radius and the bubble wall temperature lie between those obtained by the isothermal and adiabatic laws depending on the value of the Péclet number and the characteristic time scale.Article Citation - WoS: 1Citation - Scopus: 4Identification of Uncertainty Levels of Acoustic Properties of Biocomposites Under Different Mounting Conditions in Impedance Tube Tests(Institute of Noise Control Engineering, 2021) Garip Genç; Körük, Hasan; Şanlıtürk, Kenan Y.; Yusuf Saygılı; Hasan Körük; Koruk, Hasan; Saygili, Yusuf; Genc, Garip; 02.03. Department of Mechanical Engineering; 02. Faculty of Engineering; 01. MEF UniversityImpedance tube method is widely used to measure acoustic properties of materials. Although this method yields reliable acoustic properties for soft textured materials, uncertainty levels of measured acoustic properties for hard materials, including biocomposites, can be quite large, mainly due to uncertain mounting conditions. Here, the effects of mounting conditions on the acoustic properties of biocomposites in an impedance tube are investigated. First, nominally identical biocomposite samples with a diameter equal to the inner diameter of impedance tube are manufactured and their acoustic properties are determined. As hard materials practically cause fitting problems in the impedance tube, the diameters of samples are reduced, as in practice, by small amounts and acoustic properties of modified samples are determined. Furthermore, in order to match the diameters of samples to the inner diameter of impedance tube, different materials such as tape, petroleum jelly and cotton are applied around samples to close the air gap between the samples and the tube's inner wall. All the results are compared, and the uncertainty levels caused by different mounting conditions on the acoustic properties of biocomposites are identified. The results show that the transmission loss (TL) measurements are dramatically affected by the mounting conditions while the sound absorption conditions are less sensitive to the mounting conditions. The deviations in the measured TL levels are highest for the samples with tape and wax (10–15 dB). On the other hand, the deviations in the measured sound absorption coefficients are highest for the samples with cotton and tape (1–2%).Article Citation - WoS: 12Citation - Scopus: 15Modelling Small and Large Displacements of a Sphere on an Elastic Half-Space Exposed To a Dynamic Force(IOP Publishing, 2021) Hasan Körük; Körük, Hasan; 02.03. Department of Mechanical Engineering; 02. Faculty of Engineering; 01. MEF UniversitySpheres at medium interfaces are encountered in many applications, including in atomic force microscopy or indentation tests. Although the Hertz theory describes the contact mechanics between an elastic sphere and an elastic half-space for static loading and small deformations very well, there is a need to consider the density of the medium, the mass of the sphere and the radiation damping for dynamic loading to obtain reliable results. In this study, an analytical model for predicting the small and large displacements of a sphere on an elastic half-space exposed to a dynamic force is developed. For this purpose, after summarizing a mathematical model that has recently been proposed for the sphere at a medium interface, a finite element model for the sphere at an elastic interface is developed. Based on the comparison of the mathematical and finite element models, an improved analytical model for the sphere at an elastic interface is developed. In addition to considering the elastic properties of the medium and the size of the sphere, the model developed here takes into account the density of the medium, the mass of the sphere, and the radiation damping, and the model is valid for small and large sphere displacements. The developed model can be used to understand the dynamic responses of spherical objects at medium interfaces in practical applications. Furthermore, the proposed model is a remarkable tool for undergraduate and graduate students and researchers in the fields of engineering, materials science and physics to gain insight into the dynamic responses of spheres at medium interfaces. © 2021 European Physical Society.Conference Object Assessment of the Models for Predicting the Responses of Spherical Objects in Viscoelastic Mediums and at Viscoelastic Interfaces(IOP Publishing Ltd, 2021) Körük, Hasan; Körük, Hasan; 02.03. Department of Mechanical Engineering; 02. Faculty of Engineering; 01. MEF UniversitySpherical objects, such as bubbles and spheres, embedded in mediums and atviscoelastic interfaces are encountered in many applications, including the determination ofmaterial properties. This paper assesses the models for predicting the responses of sphericalobjects in viscoelastic mediums and at viscoelastic interfaces used in various applications. Themodels are presented very compactly, and evaluations are performed based on the analyses ofthe models for the spherical objects in viscoelastic mediums and at viscoelastic interfaces. First,the models for predicting the static displacements of spherical objects are presented andassessed. After that, the models for predicting the dynamic responses of spherical objects arepresented and their dynamic behaviours are compared. Then, the models for the deformation ofthe medium around spherical objects and stress distribution are presented and evaluated. Themodels and evaluations presented in this study can be exploited in various applications,including biomedical applications.Conference Object Development of a Model for Predicting Dynamic Response of a Sphere at Viscoelastic Interface: a Dynamic Hertz Model(IOP Publishing Ltd, 2021) Körük, Hasan; Körük, Hasan; 02.03. Department of Mechanical Engineering; 02. Faculty of Engineering; 01. MEF UniversityA model for predicting the dynamic response of a sphere at viscoelastic interface is presented. The model is based on Hertz contact model and the model for a sphere in a medium.In addition to the elastic properties of medium and the size of sphere, the model considers thedensity of sphere, the density and viscosity of medium, and damping of oscillations of spheredue to radiation of shear waves. The model can predict not only the effects of the mechanicalproperties of medium, the physical properties of sphere, and the amplitude of excitation forceon sphere displacement, but also the effects of these parameters on shift of resonancefrequency. The proposed model can be used to identify the elastic and damping properties ofmaterials, and to understand the dynamic responses of spherical objects at viscoelasticinterfaces in practical applications.