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Dissertations / Theses on the topic 'Viscoelastic material properties'
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1
Karlsson, Patrik. "Determination of viscoelastic properties of adhesives." Thesis, Linnéuniversitetet, Institutionen för byggteknik (BY), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-35521.
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A research project at Linnaeus University focuses on optimizing theadhesives joints between wood and glass, with the aim of obtain stiffcomponents that can act as a load and stabilizing elements and still betransparent. But there is, however, still a lack of knowledge regarding theadhesive materials which need to be further investigated. This thesis focused on testing six different adhesives in relaxation and todetermine the viscosity (η) and modulus of elastic (MOE, E). Viscosity andMOE are then used in combination in a standard linear solid model (SLS)describing the viscoelasticity mathematically. Figures and tables are used topresent the results and the evaluation. The so determined parameters can beused in e.g. finite element models for the design of load bearing timber glasscomposites.
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Iqbal, Shaheer. "Characterization of Viscoelastic Properties of a Material Used for an Additive Manufacturing Method." Thesis, University of North Texas, 2013. https://digital.library.unt.edu/ark:/67531/metadc407787/.
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Recent development of additive manufacturing technologies has led to lack of information on the base materials being used. A need arises to know the mechanical behaviors of these base materials so that it can be linked with macroscopic mechanical behaviors of 3D network structures manufactured from the 3D printer. The main objectives of my research are to characterize properties of a material for an additive manufacturing method (commonly referred to as 3D printing). Also, to model viscoelastic properties of Procast material that is obtained from 3D printer. For this purpose, a 3D CAD model is made using ProE and 3D printed using Projet HD3500. Series of uniaxial tensile tests, creep tests, and dynamic mechanical analysis are carried out to obtained viscoelastic behavior of Procast. Test data is fitted using various linear and nonlinear viscoelastic models. Validation of model is also carried out using tensile test data and frequency sweep data. Various other mechanical characterization have also been carried out in order to find density, melting temperature, glass transition temperature, and strain rate dependent elastic modulus of Procast material. It can be concluded that melting temperature of Procast material is around 337°C, the elastic modulus is around 0.7-0.8 GPa, and yield stress is around 16-19 MPa.
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Kashani, Pooria Sharif. "An ex-situ material state monitoring of curing based on viscoelastic properties in polymer composites." Thesis, Wichita State University, 2007. http://hdl.handle.net/10057/1563.
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It is well known that time and temperature are not direct measurements of either material state during cure or mechanical properties after cure in polymer composites. Rather, in current practice, the viscoelastic properties and mechanical properties during cure are merely assumed based on an extensive statistical data of time and temperature history of the material. This practice is time-consuming and costly. In this study, an ex-situ estimation of the actual material states using advanced analytical instruments has been proposed and validated. An encapsulated sample rheometer was used as the main ex-situ instrument capable of measuring with high repeatability and robustness necessary for the validation of viscoelastic curing models of composites (especially prepregs) at production level. This rheometer was coupled with Differential Scanning Calorimetry (DSC) to obtain a correlation of the key variables of curing and the actual material states. Experimental and analytical modeling studies of the viscoelastic properties and thermal properties of four commercial prepregs were conducted using these instruments. These key cure variables were directly correlated with the viscoelastic states of the material during cure. The viscoelastic properties such as storage modulus, loss modulus, and tanδ and the glass transition temperature of the Advanced Composite Group (ACG) MTM45 and MTM45-1 prepregs and Cytec 977-2 PW and 977-2 UD prepregs were measured using the rheometer during different isothermal cure cycles below the final glass transition temperature (g∞ T). Thermal analysis of 977-2 PW and 977-2 UD prepregs was obtained using the DSC and these thermal results were correlated to the rheometry measurements. Glass transition temperatures (g T) of the cure cycles were measured using both rheometry and DSC techniques. A semi-empirical curing model, based on the viscoelastic properties of prepregs, was developed and compared with the experimental data collected at a constant frequency. A process engineer could use this curing model to monitor, control, and optimize a cure process, and to aid in the curing of parts that have time and temperature history discrepancies. This model can be statistically correlated to critical composite properties and can be validated with time and temperature feedback. Therefore, temperature sensors, such as thermocouples, would remain as the primary in-situ sensors and there would be no need for material state sensors inside the autoclave or other processing units.<br>Thesis (M.S)-- Wichita State University, College of Engineering, Dept. of Mechanical Engineering<br>"December 2007."
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Kashani, Pooria Sharif Minaie Bob. "An ex-situ material state monitoring of curing based on viscoelastic properties in polymer composites /." Thesis, A link to full text of this thesis in SOAR, 2007. http://hdl.handle.net/10057/1563.
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Fincan, Mustafa. "Assessing Viscoelastic Properties of Polydimethylsiloxane (PDMS) Using Loading and Unloading of the Macroscopic Compression Test." Scholar Commons, 2015. https://scholarcommons.usf.edu/etd/5480.
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Polydimethylsiloxane (PDMS) mechanical properties were measured using custom-built compression test device. PDMS elastic modulus can be varied with the elastomer base to the curing agent ratio, i.e. by changing the cross-linking density. PDMS samples with different crosslink density in terms of their elastic modulus were measured. In this project the PDMS samples with the base/curing agent ratio ranging from 5:1 to 20:1 were tested. The elastic modulus varied with the amount of the crosslinker, and ranged from 0.8 MPa to 4.44 MPa. The compression device was modified by adding digital displacement gauges to measure the lateral strain of the sample, which allowed obtaining the true stress-strain data. Since the unloading behavior was different than the loading behavior of the viscoelastic PDMS, it was utilized to asses viscoelastic properties of the polymer. The thesis describes a simple method for measuring mechanical properties of soft polymeric materials.
6
Farukh, Farukh. "Experimental and numerical analysis of deformation and damage in thermally bonded nonwoven material." Thesis, Loughborough University, 2013. https://dspace.lboro.ac.uk/2134/12812.
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Senan, Anish Sen. "Determination of the Viscoelastic Properties of General Anisotropic Materials." Fogler Library, University of Maine, 2003. http://www.library.umaine.edu/theses/pdf/SenanAS2003.pdf.
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Eskandari, Hani. "On the identification of mechanical properties of viscoelastic materials." Thesis, University of British Columbia, 2009. http://hdl.handle.net/2429/6051.
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Commonly used medical imaging techniques can render many properties of the anatomy or function, but are still limited in their ability to remotely measure tissue mechanical properties such as elasticity and viscosity. A remote and objective palpation function would help physicians in locating possible tumors or malignancies. The branch of medical imaging that characterizes tissues mechanical properties in a non-invasive manner has enjoyed increasing interest in the past two decades. The basic principle is to apply an excitation, such as tissue compression, to a region of interest and measure the resulting tissue deformation. Tissue mechanical properties can then be inferred from the observed deformation at multiple locations in the region, and the properties can be displayed as an image. If the excitation is dynamic, the deformation is considered as a motion field that varies in time and location over the region of interest. Ultrasound is particularly well suited for measuring motion fields due to its ability to image in real-time, low cost, low risk and ease-of-accessibility. The focus of this thesis is the estimation of the viscoelastic parameters such as Young's modulus, viscosity and relaxation-time. For this purpose, a motion estimation method is proposed to measure axial tissue displacements from the peak of the ultrasound radio frequency signals. The displacements can be further processed to identify the mechanical properties. Two methods were developed: the first one is based on a one dimensional Voigt's model of soft tissue and the second one is based on a finite element model. In the first method, a single frequency or wide-band excitation is applied to the tissue and the local relaxation-time is recovered from the phase difference between the strains or displacements. In this method, the elasticity can also be reconstructed from the magnitudes of the spectra. In the second approach, a novel dynamic finite element model is proposed for the incompressible soft materials. An inverse problem of viscoelasticity is solved iteratively to reconstruct the viscosity and elasticity based on a two or three dimensional model. The theoretical aspect of compressional elastography and longitudinal wave propagation is investigated. It is shown to be feasible to apply dynamic or transient compressional excitation to recover the dynamic properties of soft tissue.
9
Biesel, Van Brian. "Experimental measurement of the dynamic properties of viscoelastic materials." Thesis, Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/19249.
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Saber-Sheikh, Kambiz. "The viscoelastic properties of some dental soft lining materials." Thesis, Queen Mary, University of London, 1997. http://qmro.qmul.ac.uk/xmlui/handle/123456789/1709.
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The viscoelastic properties of soft lining materials are of enormous interest and importance as they clearly govern the biomechanical function of these materials. Forced vibration (Non-resonant) dynamic mechanical analysis was used to characterise the viscoelastic properties of a wide range of commercial (8 brands) as well as experimental soft liners (7 formulations). Forced vibration DMA is the ideal way of studying these materials as it can closely and accurately mimic physiological temperatures and frequencies under which they operate. The materials were studied as processed, and subsequently after simulated ageing for time periods up to twelve months. The water absorption and the subsequent changes in the viscoelastic behaviour of these materials are important as they spend a large part of their working lifetime immersed in solution. The results, where possible, were compared with the work of other researchers, and any sources of discrepancy examined. It was noted that the materials whose glass to rubber transition (Tg) was near their operating temperature (i.e. the acrylics) were particularly prone to any changes in the time and temperature domain of the experiment. A large variation was observed in the properties of the commercial materials available. At 37°C and 1 Hz a seven fold range was seen in the real part of the modulus (2.79-19.7 MPa), and a fifty fold range was observed in the loss tangent (0.029-1.52). Given this wide disparity it is surprising that a universally recommended range of properties does not exist, although there is some speculation in the literature. The study of the ageing behaviour of these materials in water showed that the traditional hardening of the acrylics has been overcome. A heat cured silicone material was seen to be virtually unaffected by time, while for a cold cured competitor the opposite was true. New and experimental materials showed a wide range of behaviour after immersion in water.
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Poisl, William Howard III. "Mechanical and viscoelastic properties of materials by instrumented indentation." Diss., The University of Arizona, 1995. http://hdl.handle.net/10150/187224.
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The mechanical properties of small volumes of material have received increasing attention in the past decade due to the extensive use of films and coatings in microelectronic devices and as protection against wear and corrosion. The mechanical properties of thin films of a given material are often substantially different from those of the identical bulk material. Instrumented, or ultra-low load, indentation instruments are capable of measuring the elastic, plastic and time-dependent properties of small volumes of materials. A two stage area model has been developed to predict the variation in measured hardness with depth of penetration for soft films on hard substrates. The model is able to predict the variation for depths of penetration less than and greater than the film thickness. The model incorporates constraints on the film hardness based on the uniaxial compression of a flat cylindrical disk. Friction, or adhesion, at the film/substrate interface causes the film hardness to increase as the depth of penetration increases. However, the film hardness is not allowed to increase beyond the substrate hardness. The model is compared to experimental hardness versus depth data for three different film/substrate systems with different levels of adhesion. Time-dependent properties of materials are obtainable from instrumented indentation tests by measuring the force and displacement as a function of time. Indentation creep experiments on a linear viscoelastic material, amorphous selenium, were used to establish the relationship between indentation strain rate and the strain rate measured in conventional creep tests. Equations for determining viscosity from indentation tests were also obtained. Finally, it was shown that stress relaxation functions for viscoelastic materials may be obtainable from indentation creep experiments.
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Tsardaka, Ekaterini D. "Viscoelastic properties and compaction behaviour of pharmaceutical particulate materials." Thesis, University of Bath, 1990. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319666.
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Li, Zhuang. "Vibration and acoustical properties of sandwich composite materials /." Auburn, Ala., 2005. http://repo.lib.auburn.edu/2005%20Fall/Dissertation/LI_ZHUANG_26.pdf.
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Wu, Lei. "The dynamic properties of voided polymers." Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/16968.
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Suphadon, Nutthanun. "The viscoelastic properties of rubber under a complex loading." Thesis, Queen Mary, University of London, 2010. http://qmro.qmul.ac.uk/xmlui/handle/123456789/410.
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This thesis aims to explore the effect of pre-strain on the viscoelastic behaviour of rubber materials. There are various conflicting theories in the literature regarding the strain dependence and resulting anisotropy of the viscoelastic behaviour. This thesis seeks to measure the behaviour and to study the possibility of using Finite Element Analysis (FEA) to predict the static behaviour of a rubber cylinder in combined torsion-tension and also the viscoelastic behaviour of rubber under various complex loadings using a Bergstrom-Boyce model1-4. To measure the induced anisotropy, a rubber test piece is subjected to a simple extension l and then it is subjected to small strain oscillations in the direction of the pre-extension or in shear. These two different deformations will allow the extent of the anisotropy in the viscoelastic behaviour induced by the pre-extension to be measured. Kuhn and Kunzle5 found that the loss factor resulting from a small oscillation decreased as a function of the static pre-strain. They and many others have interpreted this as a lowering of internal viscosity due to chain orientation. However, a simple analysis shows that this effect is due to geometric changes alone and that the essential viscoelastic behaviour expressed in terms of the deformed dimension after the application of the pre-strain as the loss modulus for an unfilled rubber is constant with strain up to an extension ratio of 2. It is also isotropic in behaviour for filled rubber compounds such as carbon black. For fumed silica filled rubber, the picture is more complex. For a moderately carbon black (25 phr) filled rubber, the loss modulus is still independent of the pre-strain for normal working strains but at highly filler contents (above 50 phr), the loss modulus increases with pre-strain at extension ratios somewhat less than 2. With silica, the coupling agent dominates the viscoelastic behaviour. For filled rubber, the change in loss modulus with strain can in part be explained by strain amplification, slippage of rubber around the filler, and shape factor effects. This approach can help to further understand the mechanism of filler reinforcement in rubber materials. Another complex loading is also used to validate these results with a static pure shear superimposed with simple shear oscillation. The results confirm the loss modulus is independent of the pre-strain for unfilled rubber and lightly filled rubber but for the most highly filled rubber, the test is unsuitable as the smallest oscillating strains were too great for linear viscoelastic behaviour. The Finite Element Analysis (FEA) shows that a rubber cylinder in combined torsion-tension test can be modelled accurately as an elastic component provided that the appropriate strain energy function (SEF) and geometry are used in the model. The correct torque and the second order effect whereby a reduction in the axial force resulting from the torsion of a pre-strained rod can both be accurately represented. The viscoelastic behaviour under various complex loadings was modelled using the Bergstrom and Boyce model1. The results show that this model can predict behaviour for uniaxial but in a complex loading the model was inappropriate.
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Reiniati, Isabela. "Chemical, physical, and viscoelastic properties of hotpressed hybrid poplar." Pullman, Wash. : Washington State University, 2009. http://www.dissertations.wsu.edu/Thesis/Summer2009/i_reiniati_061209.pdf.
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Thesis (M.S. in chemical engineering)--Washington State University, August 2009.<br>Title from PDF title page (viewed on July 15, 2009). "School of Chemical Engineering and Bioengineering." Includes bibliographical references.
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Abba, Mohammed Tahir. "Spherical nanoindentation protocols for extracting microscale mechanical properties in viscoelastic materials." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54359.
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Nanoindentation has a high load resolution, depth sensing capabilities, and can be used to characterize the local mechanical behavior in material systems with heterogeneous microstructures. Recently nanoindentation has been used to extract useful stress-strain curves, primarily in hard materials such as metals and ceramics. To apply these indentation stress-strain methods to polymer composites, we have to first develop analysis techniques for materials that exhibit viscoelasticity. In a lot of current research the viscoelastic material properties are extracted after the material has been deformed enough to initiate plasticity and in some cases the time dependence of the deformation is ignored. This doesn’t give an accurate representation of the material properties of the undeformed sample or the local deformation behavior of the material. This dissertation develops analysis protocols to extract stress-strain curves and viscoelastic properties from the load-displacement data generated from spherical nanoindentation on materials exhibiting time-dependent response at room temperature. Once these protocols are developed they can then be applied, in the future, to study viscoelastic and viscoplastic properties of various mesoscale constituents of composite material systems. These new protocols were developed and tested on polymethyl methacrylate, polycarbonate, low-density polyethylene, and the bio-polymer chitosan. The properties extracted were consistent under different conditions and we were able to produce stress-strain curves for different loading rates and different indenter tip sizes. This dissertation demonstrates that a set of protocols can be used to reliably investigate the mechanical properties and deformation behavior of time-dependent materials using nanoindentation.
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Doane, John William. "Measurements on the condition of compliant coatings for prediction of acoustic performance." Thesis, Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/17588.
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Tabakci, Alican. "Mechanical Properties Identification Of Viscoelastic / Hyperelastic Materials Based On Experimental Data." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612634/index.pdf.
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Mechanical simulation of viscoelastic materials and assigning a viscoelastic
material to the modeled parts in the simulations are difficult task. For the
simulations, material model should be well chosen and material coefficients of the
chosen models should be known.
In order to obtain accurate simulations, hyperelastic characteristics of the
viscoelastic materials should be investigated and hyperelastic model should be
incorporated in the solutions. Material models and material model&rsquo<br>s coefficients are
chosen with the help of mechanical tests/experiments for these situations.
The main goal of this thesis is to optimize material model&rsquo<br>s coefficients by using an
indenter test setup results and inverse finite element modeling. To achieve this,
firstly by using a haptic device and other required equipments an indenter setup was
prepared to test the materials mechanically. Inverse finite element modeling method
is used in order to model the materials according to their viscoelastic and hyperelastic characteristics. The model obtained from analysis was optimized by
using the results obtained from indenter setup according to experimental test data.
By doing this, the correctness of the model chosen by inverse finite element
modeling was proved for the tested material and material model coefficients were
calculated correctly.
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Stone, Thomas Shannon. "A numerical/experimental method for evaluating the bulk and shear complex dynamic moduli of viscoelastic polymers in the kilohertz range." Thesis, Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/17038.
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Mahaffy, Rachel Elaine. "The quantitative characterization of the viscoelastic properties of cells and polymer gels /." Full text (PDF) from UMI/Dissertation Abstracts International, 2000. http://wwwlib.umi.com/cr/utexas/fullcit?p3004328.
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Wang, Lei. "Study on the characterization of mechanical properties of viscoelastic-plastic materials by nanoindentation." Thesis, University of Warwick, 2014. http://wrap.warwick.ac.uk/67680/.
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The aim of this PhD work is to develop a novel and effective instrument to characterize the mechanical properties of viscoelastic material. The principle of this system is based on nanoindentation technique, which is widely used in recent years to explore the mechanical properties of various materials. However, quite a few studies demonstrated that the determination of mechanical properties of viscoelastic material by using the standard Oliver Pharr method would lead to incorrect results. Based on this issue, a new improved tribological probe microscopy (TPM) system was established to carry out the investigation of mechanical properties of viscoelastic materials. Materials including polytetrafluoroethylere (PTFE), styrene rubber and nitrile rubber were measured under quasi-static mode of nanoindentation. The inaccurate results proved that static indentation analyzed by the Oliver Pharr method is not suitable for current work. In addition, dynamic indentation was performed to measure these samples. The results demonstrated that it is a good approach to explore time-dependent properties of polymer samples. The dynamic method offers more abundant viscous information. Moreover, another measurement function was added in this facility to perform creep nanoindentation on viscoelastic samples. It enables to generate instant and infinite modulus as well as time constant. The comparison between the results obtained by dynamic and creep indentation reveals that the more physical element should be considered to bridge the gap between these two approaches. Extra works focus on the relationship between surface topography and its mechanical properties. Finite element simulation as well as actual experiments were performed to investigate the tilt effect on the results of mechanical properties. The results revealed that the standard Oliver Pharr method underestimated the contact area, which will result in overestimating the hardness and elastic modulus of engineering materials. Above all, this study proved the ability of our home made facility to further explore the viscoelastic material. More importantly, it will pave a new way for the investigation of the relationship between the surface topography and viscous property of soft matter including various biomaterials in the near future.
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Lee, Hyuk. "Mechanical and viscoelastic properties of cementitious materials using statistical analysis tools and nanoindentation." Thesis, Curtin University, 2016. http://hdl.handle.net/20.500.11937/1439.
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The research presents an investigation of mechanical and nanostructure characteristics of alternative cementitious materials such as blended and alkali-activated cements using nanoindentation technology and statistical analysis tools. Findings show that the properties of the reaction products of the tested cementitious materials determined in nanoscale enable an assessment of the long-term macroscopic behaviour. Statistical analysis of these mechanical and nano characteristics of cementitious materials results in materials properties which are useful in structural engineering application.
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Zhang, Lizhong. "Physical, mechanical, thermal, and viscoelastic properties of water-blown rigid polyurethane foam containing soy flours /." free to MU campus, to others for purchase, 1998. http://wwwlib.umi.com/cr/mo/fullcit?p9924871.
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Willis, Richard Lance. "Non-invasive characterization of microvoided polymers under controlled static pressure and temperature using laser doppler vibrometry." Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/17248.
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Sullivan, Rani W. "An analytical method to determine the mechanical properties of linear viscoelastic solids." Diss., Mississippi State : Mississippi State University, 2003. http://library.msstate.edu/etd/show.asp?etd=etd-09022003-112225.
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Lai, Erica L. "Deciphering how the viscoelastic properties of mussel-inspired metal-coordinate hydrogels dictate their adhesive and interfacial mechanics." Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/127698.
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This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.<br>Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2020<br>Cataloged from student-submitted PDF of thesis.<br>Includes bibliographical references (pages 75-79).<br>In the world of adhesives, tunable viscoelasticity and adhesion to wet surfaces are two highly desirable properties. Mussels have already mastered both of these properties within the threads they create to anchor themselves in harsh intertidal conditions (collectively called the byssus). The key to both the mussel's ability to stick to a wide variety of surfaces and the highly energy-dissipative viscoelastic behavior of its byssal threads is a type of reversible bonding called metal-ligand coordination, which is comprised of amino acid functional groups binding to metal ions. Recently, researchers have incorporated metal-coordinate cross-links into various types of polymeric networks to improve their mechanical properties, particularly toughness, self-healing, and adhesion. However, there is not as much fundamental understanding of how the linear viscoelastic properties of these networks dictate adhesive behavior, both cohesively and at an interface.<br>In this thesis, we use shear rheology, tack tests, and spherical probe indentation tests to explore correlations between linear viscoelastic properties (i.e., plateau modulus, G[subscript p], and characteristic relaxation time, [tau][subscript c]) and adhesive behavior (e.g., peak stress, energy dissipation per volume or work of debonding per area) of transiently cross-linked hydrogels comprised of histidine-functionalized 4-arm PEG coordinated with Ni². It is important to note that this fully transient model system is technically a viscoelastic fluid even if it has gel-like behavior on the timescales studied. To control the viscoelastic properties of the transient networks, we varied the Ni²+-histidine ratio, the polymer wt %, or the choice of buffer; in a case study, we also added Co²+ for a second relaxation timescale. The experimental conditions of pull rate and substrate choice were also varied.<br>From our tack results, a strong dependence of peak stress on G[subscript p] and [tau][subscript c] was observed, and this correlation between network dynamics and mechanics under tensile load is in good quantitative agreement with our theoretical framework for peak stress, which includes the linear viscoelastic properties as parameters. Energy dissipation per volume is also influenced by G[subscript p] and [tau][subscript c], with an additional dependence on the polymer wt % at higher strains when the network is remodeling. These findings are consistent with previously proposed molecular mechanics of reversible His[subscript x]Ni²+ cross-links. From our ongoing spherical probe indentation tests, we have demonstrated that metal-ligand coordination at the interface can be a dominant contributor to adhesion, and we are starting to provide quantitative information about how that contribution is modulated by probe material choice and buffer-influenced timescales.<br>In addition to the adhesive studies, we also replicated the effect of the macroscopic byssal thread structure - a stiff metal-coordinate coating surrounding a compliant core - on its mechanical behavior. To do so, we mimicked the thread structure by coating PDMS fibers with dried 4-arm PEG that was end-functionalized with Dopa or nitroDopa and coordinated with Fe³⁺, and performed tensile tests on these coated fibers. From these studies, we demonstrated that the coating allowed for improved toughness, with the magnitude dependent on the coating composition (i.e. pH and covalent cross-linking content). Collectively, these findings provide us with new insights into the correlations between bulk mechanics and adhesive dynamics of gels with transient metal-coordinate cross-links, as well as ways to tune the toughness of mussel-inspired materials during larger extensions under tensile load.<br>by Erica L. Lai.<br>Ph. D.<br>Ph.D. Massachusetts Institute of Technology, Department of Materials Science and Engineering
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Mahiuddin, Md. "Mechanical characterizing and drying simulation of plant-based food materials: The fractional model approach." Thesis, Queensland University of Technology, 2020. https://eprints.qut.edu.au/204285/1/Md_Mahiuddin_Thesis.pdf.
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Food processing industry is one of the largest manufacturing sectors in Australia. Drying is one of the major processes in food industry that reduces food waste by increasing shelf-life. However, drying is highly energy-intensive lengthy process and results in significant quality deterioration. To retain the fresh like quality and reduce the energy consumption, a comprehensive understanding of transport process during drying is essential. To overcome the limitations of current mathematical models, this study introduced new fractional differential models for mechanical characterising and drying simulation of food materials. These models can be applied in many areas outside food drying.
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Sutton, Michael Philip. "Quantifying the viscoelastic properties of treated and untreated Pseudomonas aeruginosa and Staphylococcus epidermidis biofilms using a rheological creep analysis." Thesis, Montana State University, 2008. http://etd.lib.montana.edu/etd/2008/sutton/SuttonM0508.pdf.
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Microbial biofilms are quite difficult to kill and control, and present many problems to industry and medicine. The ability to alter the mechanical properties of biofilms could aid in the control of biofilm. The goal of this research project was to develop techniques for measuring the mechanical properties of biofilms so that the effects of chemical treatments could be assessed. Constitutive material models were developed and applied to assist in this effort to quantify the effects. Biofilms are viscoelastic in nature, therefore, rheological testing techniques were utilized for this research. Creep testing was performed on a parallel plate rheometer to determine biofilm mechanical properties. The rheometer is a mechanical device that can accurately measure and apply shear stress and strain on viscoelastic samples. The Burger material model closely approximated material behavior of most chemical treatments. This model was used for determining constitutive properties. Pseudomonas aeruginosa (FRD1) and Staphylococcus epidermidis colony biofilms were used for testing. Several treatment methods were used to investigate their effect on biofilm mechanical properties. As a source of different cations, solutions of NaCl, FeCl3, AlCl3, MgCl2, CaCl2, FeCl2 were used for testing. Multivalent cation treatments stiffened the FRD1 biofilm, but weakened the S. epidermidis. Urea treatments weakened both biofilm species. Glutaraldehyde treatments weakened the FRD1 biofilm, but had little effect on the S. epidermidis. Several treatments - EDTA, Barquat, chlorine, antibiotics (rifampin, and ciprofloxacin) - weakened biofilms of both species. The effect of the same chemical treatment between the two species of biofilm sometimes had nearly opposite effects on the biofilms mechanical properties. This research illustrated that it is possible to alter the mechanical properties of biofilm through chemical addition. Further, there are significant differences between the ways that the material properties of biofilms of different species of bacteria will be affected by a chemical treatment. Finally, it was observed that the 4-parameter Burger model for constitutive mechanical properties of biofilms fit the vast majority of the collected data, so that this model proves useful in comparing properties of biofilms grown or treated under various conditions.
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Debnath, Dibyendu. "SYNTHESIS AND VISCOELASTIC PROPERTIES OF GELS OBTAINED FROM LINEAR AND BRANCHED POLYMERS." University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1525400236218684.
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Debnath, Dibyendu Debnath. "SYNTHESIS AND VISCOELASTIC PROPERTIES OF GELS OBTAINED FROM LINEAR AND BRANCHED POLYMERS." University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1525398351097978.
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Salisbury, S. T. Samuel. "The mechanical properties of tendon." Thesis, University of Oxford, 2008. http://ora.ox.ac.uk/objects/uuid:97b73cf6-53bc-4606-b974-a1cdc662e9e8.
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Although the tensile mechanical properties of tendon have been well characterised, the viscoelastic and anisotropic properties remain uncertain. This thesis addresses the anisotropic and viscoelastic material properties of tendon. A method to characterise the three-dimensional shape of tendon is reported and experiments to characterise the fibre-aligned and fibre-transverse viscoelastic properties of tendon are presented. The cross-sectional profiles of bovine digital extensor tendons were determined by a laser-slice method. Linear dimensions were measured within 0.15 mm and cross-sectional areas within 1.7 mm². Tendons were compressed between two glass plates in creep loading at multiple loads. Compression was then modelled in a finite element environment. Tendon was found to be nearly incompressible and reproduction of its isochronal load-displacement curve was achieved with a neo-Hookean material model (E ≃ 0.3 MPa). The fibre-aligned tensile mechanical properties were described using a Quasi-Linear Viscoelastic model. The model was effective at reproducing cyclic loading; however, it was ineffective at predicting stress relaxation outside the scope of data used to fit the model. When all experimental results are considered together, two significant conclusions are made: (1) tendon is much stiffer in fibre-aligned tension than in fibre-transverse compression and (2) the fibre-aligned tensile response is strain dependant, while the transverse response is not.
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De, Paoli Federico. "Measuring Polydimethylsiloxane (PDMS) Mechanical Properties Using Flat Punch Nanoindentation Focusing on Obtaining Full Contact." Scholar Commons, 2015. http://scholarcommons.usf.edu/etd/5881.
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In this research, the materials used were the Polydimethylsiloxane (PDMS) polymers. PDMS mechanicals properties were measured using a customized version of the nanoindentation test using a flat punch tip. The method is proposed in Chapter 3 and it is used to calculate the elastic modulus of different PDMS samples. The samples tested were both produced specifically for this research and available in the laboratory’s storage. They all present different levels of cross-linking degree.
It is quite common to not have full contact between the cylindrical flat punch and the sample because of the unavoidable tilt. The new method guarantees establishing full contact between the sample and the tip. The tip used for this purpose is a flat punch tip. The Young’s moduli of the following samples were calculated: 10:1, 30:1 and 50:1. The Young’s moduli found were: 2.85±0.001 MPa for the 10:1 sample, 0.34±0.001 MPa for the 30:1 sample and 0.15±0.002 MPa for the 50:1 sample. All the experiments were repeated at least three times to assure the validity and the repeatability of the method. The results were then compared with values available in the literature.
The same method was applied to analyze the viscosity of the samples. Even if a mathematical result was not obtained, data and analysis through graphical representations are available in this thesis. The sample tested was a PDMS sample with a cross-linking degree of 30:1. The experiment has been repeated three times
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Claudino, Mauro. "Thiol−ene Coupling of Renewable Monomers : at the forefront of bio-based polymeric materials." Licentiate thesis, KTH, Ytbehandlingsteknik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-40267.
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Plant derived oils bear intrinsic double-bond functionality that can be utilized directly for the thiol–ene reaction. Although terminal unsaturations are far more reactive than internal ones, studies on the reversible addition of thiyl radicals to 1,2-disubstituted alkenes show that this is an important reaction. To investigate the thiol–ene coupling reaction involving these enes, stoichiometric mixtures of a trifunctional propionate thiol with monounsaturated fatty acid methyl esters (methyl oleate or methyl elaidate) supplemented with 2.0 wt.% Irgacure 184 were subjected to 365-nm UV-irradiation and the chemical changes monitored. Continuous (RT– FTIR) and discontinuous (NMR and FT–Raman) techniques were used to follow the progress of the reaction and reveal details of the products formed. Experimental results supported by numerical kinetic simulations of the system confirm the reaction mechanism showing a very fast cis/trans-isomerization of the alkene monomers (<1.0 min) when compared to the total disappearance of double-bonds, indicating that the rate-limiting step controlling the overall reaction is the hydrogen transfer from the thiol involved in the formation of final product. The loss of total unsaturations equals thiol consumption throughout the entire reaction; although product formation is strongly favoured directly from the trans-ene. This indicates that initial cis/trans-isomer structures affect the kinetics. High thiol–ene conversions could be easily obtained at reasonable rates without major influence of side-reactions demonstrating the suitability of this reaction for network forming purposes from 1,2-disubstituted alkenes. To further illustrate the validity of this concept in the formation of cross-linked thiol–ene films a series of globalide/caprolactone based copolyesters differing in degree of unsaturations along the backbone were photopolymerized in the melt with the same trithiol giving amorphous elastomeric materials with different thermal and viscoelastic properties. High thiol–ene conversions (>80%) were easily attained for all cases at reasonable reaction rates, while maintaining the cure behaviour and independent of functionality. Parallel chain-growth ene homopolymerization was considered negligible when compared with the main coupling route. However, the comonomer feed ratio had impact on the thermoset properties with high ene-density copolymers giving networks with higher glass transition temperature values (Tg) and a narrower distribution of cross-links than films with lower ene composition. The thiol–ene systems evaluated in this study serve as model example for the sustainable use of naturally-occurring 1,2-disubstituted alkenes at making semi-synthetic polymeric materials in high conversions with a range of properties in an environment-friendly way.<br>Vegetabiliska oljor som innehåller dubbelbindningar kan användas direkt för thiolene reaktioner. Trots att terminala dubbelbindningar är mycket mer reaktiva än interna visar dessa studier att den reversibla additionen av thiyl radikaler till 1,2-disubstituerade alkener är en viktig reaktion. För att undersöka tiol–ene reaktionerna, som ivolverar dessa alkener förbereddes stökiometriska blandningar av en trifunktionell propionat tiol och enkelomättade fettsyrametylestrar (metyloleat eller metyl elaidat) samt 2.0 vikt.% Irgacure 184. Dessa blandningar utsattes för 365-nm UV strålning och de kemiska förändringarna studerades. De kemiska förändringarna analyserades med olika kemiska analysmetoder; realtid RT–FTIR, NMR och FT–Raman. Dessa användes för att analysera de kemiska reaktionerna i realtid och följa bildandet av produkterna. Reaktionsmekanismen bekräftades med hjälp av experimentella data och beräkningar av numeriska och kinetiska simuleringar för systemet. Resultaten visar en mycket snabb cis/trans-isomerisering av alkenmonomeren (<1.0 min) jämfört med den totala förbrukningen av dubbelbindningarna, vilket indikerar att det hastighetsbegränsande steget kontrolleras av väteförflyttningen från tiolen till slutprodukten. Förbrukningen av den totala omättade kolkedjan är lika med tiolförbrukningen under hela reaktionen, även om bildandet av produkten gynnas från trans-enen. Detta indikerar att den första cis/trans-isomerstrukturen påverkar kinetiken. Höga tiol-ene utbyten kan enkelt erhållas relativt snabbt utan inverkan av sidoreaktioner. Detta innebär att denna reaktion kan användas som nätverksbildande reaktion för flerfunktionella 1,2-disubstituted alkenmonomerer. Vidare användes fotopolymerisation i smälta på en serie globalid/kaprolaktonbaserade sampolyestrar med varierad grad av omättnad med samma tritiol vilket resulterade i bildandet av amorfa elastomeriska material med olika termiska och viskoelastiska egenskaper. Hög omsättning (>80%) uppnåddes relativt enkelt för samtliga blandningar oberoende av den initiala funktionaliteten. Homopolymerisation av alkenen var försumbar i jämförelse med den tiol–en-reaktionen. Mängden alkengrupper har inverkan på härdplastsegenskaperna där en hög andel alken ger en nätstruktur med högre glastransitionstemperatur (Tg). Tiol–ene reaktionen utvärderades i modellsystem baserade på naturlig förekommande 1,2-disubstituterade alkener för att demonstrera konceptet med tiol-förnätade halvsyntetiska material.<br>QC 20110915
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Tunn, Isabell [Verfasser], Kerstin G. [Akademischer Betreuer] Blank, Silke [Akademischer Betreuer] Leimkühler, and Markus [Akademischer Betreuer] Linder. "From single molecules to bulk materials: tuning the viscoelastic properties of coiled coil cross-linked hydrogels / Isabell Tunn ; Kerstin G. Blank, Silke Leimkühler, Markus Linder." Potsdam : Universität Potsdam, 2020. http://d-nb.info/121999037X/34.
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Silva, Oberdan Martins. "Avaliação do efeito ambiental nas propriedades mecânicas do compósito de peek/fibra de carbono processado via moldagem por compressão a quente." Universidade de Taubaté, 2011. http://www.bdtd.unitau.br/tedesimplificado/tde_busca/arquivo.php?codArquivo=262.
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A utilização de compósitos com matrizes termoplásticas na indústria aeronáutica aparece com forte tendência de utilização na construção de aeronaves, dado o seu potencial de produção a baixo custo, a sua possibilidade de reciclagem e a facilidade na execução de reparos. Dentre os polímeros termoplásticos utilizados em compósitos, o PEEK (poli(éter-éter-cetona)) tem atraído considerável interesse como um polímero avançado de engenharia, devido ao seu desempenho mecânico, que reforçado com fibras de carbono apresenta características de resistência mecânica desejáveis para serem utilizadas em estruturas de alto desempenho. Entretanto, os compósitos poliméricos podem apresentar mecanismos de degradação quando expostos a ambientes agressivos como a elevada temperatura e umidade e também, a radiação ultravioleta. Neste sentido, o objetivo do presente trabalho é avaliar a influência do condicionamento higrotérmico e da radiação ultravioleta na propriedade mecânica de resistência ao cisalhamento interlaminar (ILSS) e no comportamento viscoelástico (DMTA) do compósito termoplástico de PEEK/fibra de carbono, assim como, avaliar a influência dos parâmetros de processamento na obtenção do compósito via moldagem por compressão a quente. Os resultados mostram que no processamento, a utilização constante de pressão durante a etapa de resfriamento do compósito é fundamental para a sua consolidação, refletindo no ensaio de resistência ao cisalhamento interlaminar (18,4 MPa). As análises viscoelásticas das amostras submetidas aos condicionamentos ambientais (higrotérmico e ultravioleta) mostram que o condicionamento que mais afetou o compósito foi o higrotérmico. As análises demonstraram que a temperatura de transição vítrea das amostras ensaiadas por condicionamento higrotérmico (Tg=115 C) foi muito afetada, comparativamente as amostras não condicionadas (Tg=147 C), indicando o efeito deletério do condicionamento higrotérmico nas amostras.<br>The use of thermoplastic matrix composites in the aerospace industry comes up with a strong tendency to use in airplane applications, because of potential low cost production, recyclability and making repairs facilities. Among the thermoplastic polymers used in composites, PEEK (poly(ether ether ketone)) has attracted considerable interest as an advanced engineering polymer due to its mechanical performance which reinforced with carbon fibers, provides mechanical strength characteristics desirable for use in high performance structures. However, polymeric composites can present degradation mechanisms when exposed to aggressive atmosphere such as high temperature and moisture, also ultraviolet (UV) radiation. This way, the aim of this study is to evaluate the influence of hygrothermal conditioning and ultraviolet radiation on the interlaminar shear strength (ILSS) mechanical property and the viscoelastic behavior (DMTA) of the PEEK/carbon fiber thermoplastic composite, and also to evaluate the processing parameters influence to make the composite via hot compression molding. The results show in this method that, the use of constant pressure is critical to its consolidation during the composite cooling step, reflecting the shear strength testing (18.4 MPa). The samples viscoelastic analysis subjected to the environmental conditioning (hygrothermal and UV) show that the hygrothermal conditioning the most affected the composite. Analysis showed that the samples glass transition temperature tested by hygrothermal conditioning (Tg=115 C) was very affected compared to non-conditioned samples (Tg=147 C), indicating the hygrothermal conditioning deleterious effect on the samples.
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Yu-TiWu and 吳育迪. "Linear viscoelastic properties of soft material." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/95492506106170777822.
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碩士<br>國立成功大學<br>土木工程學系碩博士班<br>100<br>Soft materials, which have an elastic modulus on the order of few kPa up to few MPa, are experimentally studied to determine their linear viscoelastic properties. Both of loss tangent and the magnitude of dynamic modulus are determined in a frequency and temperature range. In this work, silicone rubber, silicone gel, hydrogel and other soft materials are tested with the pendulum-type viscoelastic spectroscopy (PVS), dynamic mechanical analyzer (DMA) and the TA rheometer. For hydrogel, the tests were conducted under the wet conditions to maintain the moisture on the sample surface during the tests. Data form the commercial devices, DMA and TA, are limited to low frequency, but with some temperature changes. The PVS, at the cruet stage of design, is not able to produce data at elevated temperature, but the frequency range is up to 20 kHz. The PVS adopts a laser-based displacement measurement system to measure the deformation of the sample under torsion or bending. Applied force is generated by the magnetic interaction between a permanent magnet and a set of Helmholtz coil. It is found that smallest resolved applied stress on the specimen is on the order of 1 Pa. Loss tangent of the tested materials is on the order of 0.1, and dynamic modulus on the order of few kPa for softer samples; few MPa for less soft samples.
Through the experimental work, we tested five kinds of soft materials. They are PDMS, silicone rubber and three kinds of silicone gel. The Young's modulus and shear modulus of the materials are, respectively, about 4~7 MPa and 1.2 MPa, and their tanδ is 0.047~0.065 and 0.07, respectively, from bending and torsion tests. Specifically, Young's modulus and shear modulus of silicone rubber is 370~590 kPa, tanδ from bending and torsion test is 0.05~0.07 and 0.048~0.055. Young's modulus of silicone gel (AB), transparent silicone gel and silicone gel (orange) is 8.2~20.7 kPa, 27.5~82.6 kPa and 63.7~90.4 kPa, shear modulus is 2.6~6 kPa, 14~2 kPa and 13~28 kPa. tanδ of silicone gel (AB), transparent silicone gel and silicone gel (orange) from bending test is 0.2~0.263, 0.09~0.057 and 0.071~0.081 from torsion test is 0.21~0.3, 0.048~0.065 and 0.047~0.067.
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Shen, Wei-hsin, and 沈維信. "Nanoindentation applied to Measurement of Viscoelastic Properties of Polymer Material." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/63869965865939059474.
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碩士<br>國立成功大學<br>機械工程學系碩博士班<br>95<br>The topical subject in this study is to investigate the polymer’s time-dependent behaviors. Through the arrangements of the applied load for nanoindentation tests, the experimental results of polymers varying with time arising in the loading, unloading, dwelling, and oscillating load processes are obtained. These indentation responses offer the help to establish the mechanical model for the load-depth behavior in polymers. Based on this model, the depth solutions are solved for these applied load conditions. The PMMA and PU materials are adopted as the typical examples with a low and a high recovery respectively in polymers. The experimental results of these two materials are fitted well if the coefficients used in this model are properly given. The phase lag exhibited between the responding depth and the oscillating load is investigated to be linear proportional to frequency. The residual cavity profile of the PMMA scanned by an atomic force microscope gives the validity of accommodation assumption. The effect of the overshooting occurring in the dwelling process is also discussed.
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Ting-WeiHsu and 許庭維. "Discriminating the Viscoelastic Properties from Flow-Dependent Behavior in Porous Material." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/t56ng2.
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碩士<br>國立成功大學<br>土木工程學系<br>102<br>The porous material is a biphasic material composed of a solid skeleton and a fluid (liquid or gas) filled the voids. In addition to the effect of the rate-dependent interaction between two phases, the solid phase may exhibit intrinsic viscoelastic behavior. The physical mechanisms are different in that flow-dependent behavior varies with specimen size while viscoelastic behavior does not. Strange et al. (2013) offer an approximate model in which the poroviscoelastic load-relaxation is the product of the poroelastic and viscoelastic responses, based on constant intrinsic Poisson's ratio. The present research extends the Strange’s approximate model to include the poroviscoelastic material with time-dependent intrinsic Poisson’s ratio. We simulate three common experiments by finite element software ABAQUS and use the numerical data of different specimens to characterize the poroviscoelasticity of porous material. For poroviscoelastic materials with time-dependent intrinsic Poisson’s ratios, the characterizations are carried out by two methods: one is based on the modified approximate model, and the other is based on the solutions obtained from Laplace transform and numerical inverse transform. To obtain the intrinsic viscoelastic behavior including Poisson’s ratio without prior assumption, we suggest to measure lateral displacements in unconfined compression test or the lateral loads in confined compression tests, when the intrinsic viscoelastic behavior is dominated. Changing the specimen size and using appropriate normalization allow us to separate the poroelastic and viscoelastic responses, and thus determine both properties successfully.
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Chen, Yi-Chan, and 陳億展. "Identification of Mechanical Properties of Viscoelastic Material by a Cantilever beam." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/02001905593293704836.
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碩士<br>國立高雄第一科技大學<br>機械與自動化工程所<br>91<br>The objective of this paper is to formulate the motion equations of the lump- and distributed- parameter systems. We use a cantilever bimorph beam connect with a tip mass in contact with a viscoelastic material which is modeled by springs and dampers. To discretize the distributed parameter system by FEM, then it can be equivalent to the lump parameter system. Using the recursive least square with exponential forgetting and selecting the appropriate input waveform, the values of the parameters will be identified by the concept of error tracking. Compare how the system identification is influenced when we input the different waveforms. Further more, since the cantilever scales with its small geometry, the device can be designed specifically for mechanical measurements of microscopic systems such as living cells and biomaterials.
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Herbert, Erik G. "An experimental investigation of the elastic and viscoelastic properties of small volumes of material." 2008. http://etd.utk.edu/2008/August2008Dissertations/HerbertErikGregory.pdf.
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Palvadi, Naga Sundeep. "Measurement of material properties related to self-healing based on continuum and micromechanics approach." Thesis, 2011. http://hdl.handle.net/2152/ETD-UT-2011-08-4274.
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The ability of an asphalt mix to heal is an important property that influences the overall fatigue performance of the mix in the field. Micro damage healing in an asphalt mix is a function of several factors such as the physical and chemical properties of the binder, properties of the mixture, level of damage prior to the rest period during which healing occurs, duration of the rest period, temperature, and pressure. This thesis presents details from a two-part study that addresses the following aspects. In the first part of this study, a DSR based test method was developed to measure inherent healing in asphalt binder and a modified form of the Avrami equation was used to model it. In the second part of this study, an experimental and analytical method based on viscoelastic continuum damage theory was developed to characterize the healing in an asphalt composite (fine aggregate matrix) as a function of the level of damage prior to the rest period and the duration of the rest period. The intrinsic healing of three different asphalt binders was measured at three different temperatures and two aging conditions and it was further demonstrated to be the sum of two components: instantaneous strength gain immediately upon wetting and time dependent strength gain. The intrinsic healing results obtained from the DSR tests were demonstrated to be in agreement with the hypothesis that time dependent intrinsic healing increases with an increase in temperature and decreases with aging of the asphalt binder. The overall healing was measured in four different fine aggregate matrix (FAM) asphalt mixes and various tests were performed to quantify overall healing at isothermal and short term aged test conditions. Additionally two different verification tests were also conducted to demonstrate that the percentage healing measured using the proposed method are independent of the sequence of loading or rest periods. Finally, the overall healing results were demonstrated to support the hypothesis that the healing characteristics determined using the proposed test method can be treated as a characteristic material property.<br>text
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Palátová, Jana. "Vliv přírodní kosmetiky na změnu mechanických vlastností kůže." Master's thesis, 2016. http://www.nusl.cz/ntk/nusl-345287.
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Charles University in Prague, Faculty of Pharmacy in Hradec Kralove Department of biophysics and physical chemistry Candidate: Bc. Jana Palátová Supervisor: Mgr. Monika Kuchařová, Ph.D. Title of thesis: The effect of natural cosmetics on chase the mechanical properties of the skin This thesis in theoretical part deals with the structure of skin, its biochemistry and functions. Discusses the changes that the skin undergoes during development and aging. It describes the mechanical properties of the skin and the discipline that deals with these characteristics. The practical part deals with the measurement of mechanical parameters of human skin after application of a natural cream. The trial involved a total of ten women were about the same age. Measurements were performed on a dynamic elastomers being developed at the Department of Biophysics and Physical Chemistry of the Faculty of Pharmacy at Charles University in Hradec Kralove. The investigated parameters were Hooke and Newton factor. Hooke's coefficient indicates the elasticity of the skin, Newton coefficient of its viscosity. The results show that the test cream affected as skin elasticity, and its viscosity. In 90 % of the test persons there was a significant increase in the values of the Hooke and Newton coefficient and the resulting effect...
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Fatseyeu, Arkadz. "Determination of properties of viscoelastic materials by nanoindentation." Thesis, 2005. http://spectrum.library.concordia.ca/9160/1/MR20759.pdf.
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The purpose of this work was to explore the possibility of measuring properties of viscoelastic materials by nanoindentation. Indentation is not a common method for determining properties of viscoelastic materials and nanoindentation is a very new, state-of-the art technology. Therefore, this research is one of very few works in this area. This study includes nanoindentation experiments on viscoelastic materials, determining bulk properties of the same materials by conventional rheological techniques, suggesting of physical models to measure properties of viscoelastic solids and viscoelastic liquids by nanoindentation and numerical simulations of the nanoindentation process. The experimental part includes nanoindentation tests of viscoelastic solids and viscoelastic liquids and comparing measured local properties with the bulk ones. The bulk properties were measured with SAOS and Torsion tests. For this investigation polybutadiene was selected as an example of a viscoelastic liquid and silicon cross-linked rubber as a viscoelastic solid. It was found that the local properties of solid polymers vary widely. However, by averaging data collected from various locations, the bulk properties can be determined accurately for the viscoelastic solids. For the physical modeling we validated the Sneddon & Sakai model of indentation of viscoelastic solids and suggested a model for the indentation of viscoelastic liquids, based on Stoke's theory of a potential flow around a sphere. Also nanoindentation of a viscous liquid was simulated using the FLUENT commercial code. It was found that for the indentation of viscoelastic materials with dominantly viscous properties, the indentation model developed from Stoke's theory gives realistic values for shear forces, but predicts a smaller than actual compression force, acting on the surface of the indenter. The comparison of the results of the mentioned above different approaches allowed us to draw conclusions about the advantages and limitation of the technology and theoretical analysis of nanoindentation and its application in rheometry. It was shown that nanoindentation can be successfully used for investigation of viscoelastic materials. Because of its unique abilities nanoindentation will become an irreplaceable tool in such areas as the testing of thin films, study of materials in a transient states, and biomedical research. However, there are number of technical and theoretical issues that need to be addressed. We outlined issues that need to be resolved and suggested direction for further research and development. Among them are: selection of a proper model to simulate behavior of particular viscoelastic material, further improvement of indentation control and data acquisition system, manufacturing new indenters of optimum shape and material
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Lee, Taeyong. "Viscoelastic properties of biological and high-damping composite materials." 2001. http://www.library.wisc.edu/databases/connect/dissertations.html.
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Chih-ChinKo and 柯智欽. "Extreme viscoelastic and coupled-field properties of negative-stiffness composite materials." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/85229302358634018916.
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博士<br>國立成功大學<br>土木工程學系<br>103<br>Negative-stiffness (NS) composite materials consist of inclusions with negative bulk modulus, Young’s modulus or shear modulus, that are embedded in positive matrix. Elastic isotropy is assumed for the inclusion. Experimental evidence from composites having ferroelastic inclusions, such as barium titanate, in the vicinity of solid-solid phase transformation supports the use of negative stiffness in theoretical and numerical modeling. Extreme effective properties, such as extremely large or small effective viscoelastic moduli, damping and coupled-field coefficients, of the composite materials can be realized if negative stiffness in inclusions is allowed, hence bounds of composite materials can be broken. Stability of the NS composites requires considerations in thermodynamics, continuum mechanics and coupled-field theories, as well as the Lyapunov stability analysis. In addition to using the theory of composite materials to predict their effective properties under the effects of negative stiffness in this dissertation, numerical calculations based on finite element methods are employed to study the effective elastic, viscoelastic, thermoelastic, piezoelectric and dielectric properties of the NS composite systems. Furthermore, their stability is determined through monitoring divergence of field variables when the system is under small sinusoidal perturbation on the boundary in the time domain analysis. Connections between material stability and numerical stability are established in the finite element time-domain analysis. Stability boundaries, in terms of allowable amounts of negative stiffness, are identified for all of the studied effective properties, including the coupled-field properties. It is found that all of the extreme properties occur in the unstable regime, except for the piezoelectric and thermal expansion properties. The multiphysics effects in the coupled-field properties may provide a stabilizing mechanisms when inclusion volume fraction is large, and inclusions are electrically insulated. In addition, stability of the NS viscoelastic systems is superior to their purely elastic counterparts due to damping mechanisms. When time-dependent material properties are considered, the divergent rate of the instability phenomena can be controlled by damping in the composite systems. Hence, the extreme properties of the NS composites may be considered as metastable. In addition to research in the negative-stiffness composite materials, conventional composite materials that simultaneously exhibit high stiffness and high damping are studied through the combination of ‘microstructured’ soft metal and polymer. In small deformation, the composite exhibits large damping due to the viscoelasticity of polymer. In large deformation, the soft metal provides energy-dissipation capabilities through plastic deformation. Through suitable design, the viscoelastic composite material may be used as a beam-column connector in civil engineering.
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Cuong, Nguyen Thanh, and 阮清強. "Characterization of Viscoelastic Properties of Composite Polymer Films and Biological Materials." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/10161736177612449620.
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碩士<br>南台科技大學<br>機械工程系<br>97<br>In this study, time dependent mechanical properties of magnetic polymer films, leafstalks of Caladium (Caladium x hortulanun Birdsey) and Giant Taro (Alocasia macrorrhiza) leafstalks were investigated. Firstly, the influence of weight ratios of magnetite nano-particles on the time dependent mechanical properties of hybrid copolymer films was investigated. The viscoelastic properties of these polymer films with 0%, 20% and 40% of magnetite nano particles were studied. Ramp-hold experiments were performed by using a custom-made tension testing apparatus to evaluate the time dependent stress-strain behavior of magnetic polymer films under uniaxial tensile load at different loading strain rates. It can be seen that, the magnetite nano-particles weight percentage of polymer has a strong effect on the stress-strain relations of polymer films. The polymer with a higher weight ratio of magnetite nano-particles can sustain higher stress under the same test condition. Experimental data were fitted into 3, 5 and 7 parameter linear viscoelastic models. It is shown that the 7-parameter Wiechert model leads to better curve-fitting results for the magnetic polymer material under ramp-hold experiments. Secondly, the mechanical properties of Caladium (Caladium x hortulanun Birdsey) and Giant Taro (Alocasia macrorrhiza) leafstalks were investigated. The leafstalk was considered as composite beam consists of Skin (Epidermis and Collenchymas) and Core (Pith and Vascular bundles) parts. In order to classify the mechanical properties of Skin and Core part of leafstalks, three-point bending tests were conducted on the specimens cut from whole leafstalk (Skin and Core) and Core only parts. Linear beam theory was used to convert the time dependent force-displacement relation during the three-point bending tests to the time dependent stress-strain relation. The linear viscoelastic constitutive model was used to describe the time dependent stress-strain behavior of Skin and Core of Caladium and Giant Taro leafstalk.
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Herbert, Erik Gregory. "An Experimental Investigation of the Elastic and Viscoelastic Properties of Small." 2008. http://trace.tennessee.edu/utk_graddiss/446.
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The purpose of this work is to further develop experimental methodologies using flat punch nanoindentation to measure the constitutive behavior of viscoelastic solids in the frequency and time domain. The reference material used in this investigation is highly plasticized polyvinylchloride (PVC) with a glass transition temperature of -17 degrees Celsius. The nanoindentation experiments were conducted using 103 and 983 micron diameter flat punches. For comparative purposes, the storage and loss modulus obtained by dynamic mechanical analysis are also presented. Over the frequency range of 0.01 to 50 Hz, the storage and loss modulus measured using nanoindentation and uniaxial compression are shown to be in excellent agreement. The creep compliance function predicted from nanoindentation data acquired in the frequency domain is also found to be in excellent agreement over two decades in time with the creep compliance function measured using a constant stress test performed in uniaxial compression. A constraint factor of 1.55 is found to overlay the creep compliance function measured by nanoindentation in the time domain with the creep function measured in uniaxial compression.
A new method is proposed to determine the elastic modulus and residual stress of free-standing thin films based on nanoindentation techniques. The experimentally measured stiffness-displacement response is applied to a simple membrane model that assumes the film deformation is dominated by stretching as opposed to bending. Experimental verification of the method is demonstrated for Al/0.5 weight percent Cu films nominally 22 microns wide, 0.55 microns thick, and 150, 300, and 500 microns long. The estimated modulus for the four freestanding films matches the value measured by electrostatic techniques within 2 percent, and the residual stress within 19.1percent. The difference in residual stress can be completely accounted for by thermal expansion and a modest change in temperature of 3 degrees Celsius.
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Brindle, Eric Robert. "The effect of treatments on the mechanical properties of Staphylococcus epidermidis biofilms under fluid shear and mechanical indentation." 2009. http://etd.lib.montana.edu/etd/2009/brindle/BrindleE1209.pdf.
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Phong, Duong The, and 楊世豐. "Investigation of Viscoelastic Properties of Hydrodels and Magnetic Polymer Thin Films materials." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/86690654736600704595.
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碩士<br>南台科技大學<br>機械工程系<br>96<br>Polymers have many applications in the biomedical field. For example, high strength hydrogel has the potential to be used to repair the damaged articular cartilage due to its low friction and high mechanical strength and bio-compatability. Besides, shape memory magnetic polymer films have the potential to be used as active medical devices. In this research, viscoelastic properties of PAA-Alg-Si hydrogels with different silica weight percentages were investigated. The experiments were performed under uniaxial test and the experiment data were fitted into linear viscoelastic constitutive models. it can be seen that the mechanical properties of PAA-Alg-Si hydrogels is strongly dependent on the weight percentage of Silica in PAA-Alg-Si hydrogels. Furthermore, mechanical properties of hybrid poly (MMA-co-MAA-co-BA) copolymer films with different weight ratios of magnetite (Fe3O4) nano particles were also investigated. The influence of weight ratios of magnetite (Fe3O4) nano-particles on the time dependent mechanical properties of hybrid copolymer films was investigated. Linear viscoelastic models have been used to provide proper fits to the time dependent stress strain relations of aforementioned copolymer film material. It can be seen that the magnetite nano-particles weight percentage of polymer films has strong effect on the stress-strain relations of polymer films.