Dissertations / Theses: 'Stress and Strain (Materials)'

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Julian, Michael Robert. "Material characterization of viscoelastic polymeric molding compounds." Connect to resource, 1994. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1137616726.

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Thesis (M.S.)--Ohio State University, 1994.
Advisors: Vernal H. Kenner and Carl H. Popelar, Dept. of Engineering Mechanics. Includes bibliographical references (leaf 106). Available online via OhioLINK's ETD Center

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Soediono, Andy H. "Near tip stress and strain fields for short elastic cracks." Diss., Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/19557.

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Kyriazopoulos, Antonios. "Mechanical stress induced electrical emissions in cement based materials." Thesis, Brunel University, 2009. http://bura.brunel.ac.uk/handle/2438/4037.

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This work deals with the underlying physical mechanisms and processes that dominate the fracture of cement based materials and their electrical properties. Electric current emissions were recorded when hardened cement pastes and cement mortars suffered mechanical loading in various modes. Such electric current emissions are known as Pressure Stimulated Currents (PSC) when the applied loading is compressional while they are mentioned as Bending Stimulated Currents (BSC) when the material suffers bending loadings. The physical mechanism responsible for the PSC and BSC emissions can be interpreted in terms of the Moving Charged Dislocations model that correlates mechanical deformation and electric charge distortions in the sample bulk. Laboratory experiments were designed based on the mechanical and physical properties of cement. To conduct the experiments all the background material concerning cement fracture mechanics, the microstructure of the hardened cement paste and the Interfacial Transition Zone of cement mortar were taken into consideration. Additionally, the experience of the PSC technique when it was applied on marble samples was used to guide the experimental procedures and compare qualitatively and quantitatively the experimental results. The relationship between the emitted PSC and the strain was established for the very first time for cement based materials in the present work. When the material was stressed within the range where stress and strain are linearly related a linear relation between PSC and stress rate (d/dt) was observed. Deviation from this linearity appeared when the applied stress was in the range where the applied stress and the yielded strain were not linearly related. Slightly before fracture, intense, non-linear PSC emissions were detected. The damage of the sample structure due to excessive loading in the plastic region significantly affected the recorded phenomena. Bending tests proved that similar electric current emissions are detected when a sample beam suffers 3 Point Bending Tests. The dependence of the emitted electric current on the way of fracture (i.e. compressional or tensional) was proved. It was also shown that the magnitude of the emitted electric current is directly related to the magnitude of damage due to the external loading. Thus, as it was expected, the electric current emitted from the tensed zone is significantly greater than the corresponding emitted from the compressed zone.

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Jones, Eric James Ph D. Massachusetts Institute of Technology. "Nanoscale quantification of stress and strain in III-V semiconducting nanostructures." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/98578.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 142-149).
III-V semiconducting nanostructures present a promising platform for the realization of advanced optoelectronic devices due to their superior intrinsic materials properties including direct band gap energies that span the visible light spectrum and high carrier mobilities. Additionally, the inherently high surface-to-volume ratio of nanostructures allows for the efficient relaxation of stress enabling the realization of defect free heterostructures between highly mismatched materials. As a result, nanostructures are being investigated as a route towards the direct integration of III-V materials on silicon substrates and as platforms for the fabrication of novel heterostructures not achievable in a thin film geometry. Due to their small size, however, many of the methods used to calculate stress and strain in 2D bulk systems are no longer valid as free surface effects allow for relaxation creating more complicated stress and strain fields. These inhomogeneous strain fields could have significant impacts on both device fabrication and operation. Therefore, it will be vital to develop techniques that can accurately predict and measure the stress and strain in individual nanostructures. In this thesis, we demonstrate how the combination of advanced transmission electron microscopy (TEM) and continuum modeling techniques can provide a quantitative understanding of the complex strain fields in nanostructures with high spatial resolutions. Using techniques such as convergent beam electron diffraction, nanobeam electron diffraction, and geometric phase analysis we quantify and map the strain fields in top-down fabricated InAlN/GaN high electron mobility transistor structures and GaAs/GaAsP core-shell nanowires grown by a particle-mediated vapor-liquid-solid mechanism. By comparing our experimental results to strain fields calculated by finite element analysis, we show that these techniques can provide quantitative strain information with spatial resolutions on the order of 1 nm. Our results highlight the importance of nanoscale characterization of strain in nanostructures and point to future opportunities for strain engineering to precisely tune the behavior and operation of these highly relevant structures.
by Eric James Jones.
Ph. D.

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Moseson, Alexander J. Barsoum M. W. Barsoum M. W. "Spherical nanoindentation : insights and improvements, including stress-strain curves and effective zero point determination /." Philadelphia, Pa. : Drexel University, 2007. http://hdl.handle.net/1860/1868.

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Seki, Wataru. "Analysis of strain localization in hyperelastic materials, using assumed stress hybrid elements." Diss., Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/19088.

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Falola, Adekunle Samuel. "MECHANICAL CHARACTERIZATION – MONOTONIC MICRO-TENSILE, STRESS RELAXATION, AND STRAIN-CONTROLLED CYCLIC STRESS-STRAIN RESPONSES OF SINGLE ELECTROSPUN PVDF NANOFIBERS." University of Akron / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=akron1564557199987647.

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Basu, Sandip Barsoum M. W. "On spherical nanoindentation stress-strain curves, creep and kinking nonlinear elasticity in brittle hexagonal single crystals /." Philadelphia, Pa. : Drexel University, 2008. http://hdl.handle.net/1860/2904.

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Qiu, Pei. "Stress-strain behaviour of cold-worded materials in cold-formed stainless steel sections." Thesis, University of Macau, 2011. http://umaclib3.umac.mo/record=b2493011.

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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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Earhart, Elizabeth Jane. "Experimental investigation of stress and strain fields in a ductile matrix surrounding an elastic inclusion." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/10359.

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Locke, Christopher William. "Stress-Strain Management of Heteroepitaxial Polycrystalline Silicon Carbide Films." Scholar Commons, 2011. http://scholarcommons.usf.edu/etd/3211.

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Silicon carbide (SiC) is one of the hardest known materials and is also, by good fortune, a wide bandgap semiconductor. While the application of SiC for high-temperature and high-power electronics is fairly well known, its utility as a highly robust, chemically-inert material for microelectrical mechanical systems (MEMS) is only beginning to be well recognized. SiC can be grown on both native SiC substrates or on Si using heteroepitaxial growth methods which affords the possibility to use Si micromachining methods to fabricate advanced SiC MEMS devices. The control of film stress in heteroepitaxial silicon carbide films grown on polysilicon-on-oxide substrates has been investigated. It is known that the size and structure of grains within polycrystalline films play an important role in determining the magnitude and type of stress present in a film, i.e. tensile or compressive. Silicon carbide grown on LPCVD polysilicon seed-films exhibited a highly-textured grain structure and displayed either a positive or negative stress gradient depending on the initial thickness of the polysilicon seed-layer. In addition a high-quality (111) oriented 3C-SiC on (111)Si heteroepitaxial process has been developed and is reported. SiC MEMS structures, both polycrystalline (i.e., poly-3C-SiC) and monocrystalline (i.e., 3C-SiC) were realized using micromachining methods. These structures were used to extract the stress properties of the films, with a particular focus on separating the gradient and uniform stress components.

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Leung, Janet (Janet H. ). "Effect of volume fraction of solids on the compressive stress-strain behavior of collagen-glycosaminoglycan scaffolds." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/35062.

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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006.
Includes bibliographical references (leaf 35).
This thesis aims to examine the effect of volume fraction of solids in collagen-glycosaminoglycan (GAG) scaffolds on the compressive-strain behavior of the structure and compare these results to the open-cell foam model. Collagen-GAG (CG) scaffolds have been used for regenerating skin, conjunctiva, and peripheral nerves with varying levels of success. In these uses, the temporary scaffolds are often deployed with a non-degradable support structure such as a waterproof film or a silicone neural tube which are removed after healing is complete if it is outside the body (for skin regeneration) or are expected to remain permanently in the body (for nerve regeneration). Unfortunately, leaving non-degradable implants in the body could provoke immune responses. At the same time, to remove supports that have been implanted in the body after healing has been completed would result in more injury to the site and other medical complications. For a truly temporary implant, the scaffold must in its entirety be degradable. Thus, the bulk mechanical properties of the scaffold are important to study. Previous research has concentrated on the effects of cells on the scaffolds on a microlevel. However, the scaffold must also be able to bear mechanical stress from surrounding tissues to keep the wound open and provide mechanical support for the body, if, for example, collagen or bone is being regenerated. Here, the bulk mechanical properties of the scaffold are tested under uniaxial, unconfined compression. The Young's modulus and critical stress are calculated from the experimental data and compared to the values predicted by the open-celled foam model. There is very good agreement between the low density scaffolds, with variability in the results increasing with increasing density and with hydration of the specimens. Further research should focus on the
(cont.) However, the scaffold must also be able to bear mechanical stress from surrounding tissues to keep the wound open and provide mechanical support for the body, if, for example, collagen or bone is being regenerated. Here, the bulk mechanical properties of the scaffold are tested under uniaxial, unconfined compression. The Young's modulus and critical stress are calculated from the experimental data and compared to the values predicted by the open-celled foam model. There is very good agreement between the low density scaffolds, with variability in the results increasing with increasing density and with hydration of the specimens. Further research should focus on the origins and the effects of heterogeneities observed in the scaffold structures on the mechanical behavior.
by Janet Leung.
S.B.

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14

Keller, Michael Scott. "A novel approach to predict current stress-strain response of cement-based materials in infrastructure." Diss., The University of Arizona, 2001. http://hdl.handle.net/10150/289742.

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This report describes the experimental and analytical results for the development of a methodology for predicting the stress-strain response of simulated concrete (mortar) in infrastructure. Lamb wave analysis is used to predict material properties of mortar specimens, which are used in the initial research as a substitute for concrete. The mortar specimens are tested to measure their stress-strain response under uni-axial compression. The results of the nondestructive and mechanical stress-strain testing are correlated to develop the model based on the Disturbed State Concept (DSC), a unified approach for modeling material behavior. This information can be used to design rehabilitation strategies, and can also lead to the development of new computer based equipment that can be used in the field for defining the remaining life. At this time, the research involved one-dimensional testing. The proposed methodology can, however, be extended and improved by conducting two- and three-dimensional testing of concrete specimens, along with laboratory and field validations.

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Owens, Anthony Taylor Tippur Hareesh V. "Development of a split Hopkinson tension bar for testing stress-strain response of particulate composites under high rates of loading." Auburn, Ala., 2007. http://repo.lib.auburn.edu/Send%2002-04-08/OWENS_ANTHONY_54.pdf.

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Wu, Xianping Kalidindi Surya Doherty R. D. "Prediction of crystallographic texture evolution and anisotropic stress-strain response during large plastic deformation in alpha-titanium alloys /." Philadelphia, Pa. : Drexel University, 2006. http://hdl.handle.net/1860/1122.

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Zhao, Yixiang. "Effects of Laser Shock Peening on Residual Stress, Texture and Deformation Microstructure of Ti-6Al-4V Alloy." University of Cincinnati / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1353343745.

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Kaya, Mustafa. "A Study On The Stress-strain Behavior Of Railroad Ballast Materials By Use Of Parallel Gradation Technique." Phd thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/3/12605026/index.pdf.

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The shear strength, elastic moduli and plastic strain characteristics of scaled-down ballast materials are investigated by use of the parallel gradation technique. Uniformly graded ballast materials chosen for the investigation are limestone, basalt and steel-slag. Steel-slag is a byproduct material of Eregli Iron and Steel Works, which is suitable to meet the durability test requirements as well as the electrical resistivity and the waste contaminants regulatory level. Conventional triaxial testing at a strain rate of 0.4 mm/min is used to obtain these characteristics for the scaled-down materials with a diameter of 100 mm specimen under a confining stress of 35 kPa, 70 kPa and 105 kPa
whereas that of only 35 kPa is used to characterize the accumulated plastic strain. The angle of internal friction, f, and the apparent cohesion, c, may be conservatively taken to be 42o and 35 kPa for all materials. The elastic moduli values for all materials may be predicted within an adequate estimate for the engineering purposes by using the power law parameters, K and n, determined for L-9.5 (D50 = 12.7 mm), the coarsest gradation tested for limestone. K with a reference pressure, pr = 1 kPa and n values for L-9.5, respectively, are 4365 and 0.636 for initial
8511 and 0.419 for secant
25704 and 0.430 for unloading-reloading elastic moduli. The unloading-reloading moduli increased, as the number of cycles increased. An increase in unloading-reloading modulus at N = 20 obtained was roughly 15% for scaled-down limestone
10% for the basalt
and 5% for the steel-slag. The plastic strain after first cycle, &
#949
1, and the plastic strain coefficient, C can be represented as a function of mean particle size for each material type. For the limestone, basalt and steel-slag prototype size, D50 = 45 mm, &
#949
1 values of 0.59, 0.43 and 0.75 and C values of 0.54, 1.42 and 0.74 are predicted, respectively.

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Deibler, Lisa Anne. "Effects of Temperature, Stress State, and Strain Rate on Flow and Fracture of Mg Metallic Glass and Viscous Fluids." Cleveland, Ohio : Case Western Reserve University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=case1238707832.

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Hu, Ruilong. "Scale and stress effects on the behavior of ferromagnetic materials." Click to view the E-thesis via HKUTO, 2007. http://sunzi.lib.hku.hk/hkuto/record/B38943232.

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Hu, Ruilong, and 胡瑞龍. "Scale and stress effects on the behavior of ferromagnetic materials." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2007. http://hub.hku.hk/bib/B38943232.

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Noriega, Motta Julio Amilcar. "Portable transparent indenter instrumentation for material surface characterization." Morgantown, W. Va. : [West Virginia University Libraries], 2006. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=4765.

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Thesis (Ph. D.)--West Virginia University, 2006.
Title from document title page. Document formatted into pages; contains xiii, 105 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 97-98).

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Oatway, Wayne Brian. "Time resolved study of the deformation of polyethylene at high strain rates using X-ray diffraction and stress-strain techniques." Thesis, Keele University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263196.

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Pryce, A. W. "Matrix cracking and stress/strain behaviour of continuous fibre ceramic composite laminates." Thesis, University of Surrey, 1991. http://epubs.surrey.ac.uk/843150/.

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Matrix damage and its effects on mechanical properties have been examined for SiC (Nicalon1) fibre reinforced glass and glass ceramic matrix composites under quasi-static and fatigue loading conditions. Nicalon/Pyrex laminates of different lay-ups have been tested under quasi-static tension. The elastic moduli have been measured and matrix damage monitored as a function of applied strain. The mechanical properties are strongly influenced by the presence of crystalline regions in the matrix which promote microcracking. Laminated plate theory is used to provide bounds to the moduli of the laminates. For unidirectional and simple crossply Nicalon/CAS2 laminates the quasi-static stress/strain behaviour and associated matrix damage accumulation have been examined in detail. The damage development with applied stress was quantified by counts of crack density (in both longitudinal and transverse plies), stiffness loss and cumulative residual strain. The quasi static stress/strain behaviour during continuous tests (accumulating damage) and discontinuous tests (constant damage) have been modelled using a stress analysis based on Aveston, Cooper and Kelly (ACK) theory. The continuous stress/strain behaviour of (0/90) crossply laminates has been modelled using a shear-lag analysis developed previously to describe the transverse ply cracking behaviour of polymer matrix composites. The analysis is modified to account for longitudinal ply cracking. Matrix damage development in unidirectional and (0/90) crossply laminates under quasistatic cycling and high frequency fatigue loading have been studied. For unidirectional laminates stable stress/strain hysteresis loops were obtained during quasi-static cycling, corresponding to stable matrix damage states. These and similar loops obtained after high frequency fatigue are modelled using, the discontinuous stress/strain analysis. It is suggested that the effect of high frequency fatigue is to decrease the interfacial shear strength.

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Seong, Jinwook. "Inhibition of Corrosion and Stress Corrosion Cracking of Sensitized AA5083." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1429701294.

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Zhao, Huyue. "Stress Analysis of Tapered Sandwich Panels with Isotropic or Laminated Composite Facings." Fogler Library, University of Maine, 2002. http://www.library.umaine.edu/theses/pdf/ZhaoH2002.pdf.

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CIONE, FRANCISCO C. "Medidas de tensões residuais por extensiometria em componentes usados no setor da mobilidade." reponame:Repositório Institucional do IPEN, 2012. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10163.

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Made available in DSpace on 2014-10-09T12:35:29Z (GMT). No. of bitstreams: 0
Made available in DSpace on 2014-10-09T14:05:35Z (GMT). No. of bitstreams: 0
Dissertação (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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Sheikh, Amiri Meisam [Verfasser], and Christian [Akademischer Betreuer] Boller. "On the microstructural stress and strain behavior determination of metallic materials based on electromagnetic phenomena / Meisam Sheikh Amiri. Betreuer: Christian Boller." Saarbrücken : Saarländische Universitäts- und Landesbibliothek, 2015. http://d-nb.info/1109790201/34.

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Dunford, Kristin Marie. "Effect of Postmortem Time and Preservation Fluid on the Tensile Material Properties of Bovine Liver Parenchyma." Thesis, Virginia Tech, 2017. http://hdl.handle.net/10919/90179.

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The liver is one of the most frequently injured abdominal organs in motor vehicle collisions. Although previous studies have quantified the tensile failure properties of human liver parenchyma at 48hrs postmortem, it is currently unknown how the material properties change between time of death and 48hrs postmortem. Therefore, the purpose of this study was to quantify the effects of postmortem degradation on the tensile material properties of bovine liver parenchyma when stored in DMEM or saline. Fourteen fresh bovine livers were obtained from a local slaughter house and stored in either DMEM or saline as large blocks, small blocks, or slices of tissue. Multiple parenchyma dog-bone samples from each liver were tested once to failure at three time points: ~6hrs, ~24hrs, and ~48hrs postmortem. The data were then analyzed to determine if there were significant changes in the material properties with respect to postmortem time. The results showed that the failure strain decreased significantly between 6hrs and 48hrs after death when stored as large blocks in saline. Conversely, neither the failure stress nor failure strain changed significantly with respect to postmortem time when stored as large blocks in DMEM. The modulus did not significantly change for tissue stored as large blocks in either fluid. Preliminary results indicated that reducing the tissue storage size had a negative effect on the material properties and cellular architecture. Overall, this study illustrated that the effects of postmortem liver degradation varied with respect to the preservation fluid, storage time, and storage block size.
MS

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Richardson, Ian R. "The stress-strain behaviour of dry granular material subjected to repeated loading in a hollow cylinder apparatus." Thesis, University of Nottingham, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287191.

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Martin, Diaz Ulises. "STRESS CORROSION CRACKING OF AUSTENITIC STAINLESS STEEL REBAR IN SIMULATED CONCRETE PORE SOLUTION INFLUENCED BY STRAIN-INDUCED MARTENSITIC TRANSFORMATION." University of Akron / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=akron1626520184452948.

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Yamashita, Tatsuya. "Analysis of anisotropic material." Ohio : Ohio University, 1996. http://www.ohiolink.edu/etd/view.cgi?ohiou1177700236.

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Angelides, Michael. "Stress compatible finite elements for bimaterial interface problems." Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=63808.

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Kemper, Andrew Robb. "Material Properties of Human Rib Cortical Bone from Dynamic Tension Coupon Testing." Thesis, Virginia Tech, 2005. http://hdl.handle.net/10919/43709.

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The purpose of this study was to develop material properties of human rib cortical bone using dynamic tension coupon testing. This study presents 117 human rib cortical bone coupon tests from six cadavers, three male and three female, ranging in age from 18 to 67 years old. The rib sections were taken from the anterior, lateral, and posterior regions on ribs 1 through 12 of each cadaver's rib cage. The cortical bone was isolated from each rib section with a low speed diamond saw, and milled into dog bone shaped tension coupons using a small computer numerical control machine. A high-rate servo-hydraulic Material Testing System equipped with a custom slack adaptor, to provide constant strain rates, was used to apply tension loads to failure at an average rate of 0.5 strains/sec. The elastic modulus, yield stress, yield strain, ultimate stress, ultimate strain, and strain energy density were determined from the resulting stress versus strain curves. The overall average of all cadaver data gives an elastic modulus of 13.9 GPa, a yield stress of 93.9 MPa, a yield strain of 0.883 %, an ultimate stress of 124.2 MPa, an ultimate strain of 2.7 %, and a strain energy density of 250.1 MPa-strain. For all cadavers, the plastic region of the stress versus strain curves was substantial and contributed approximately 60 strain % to the overall response and over 80 strain % in the tests with the 18 year old cadaver. The rib cortical bone becomes more brittle with increasing age, shown by an increase in the modulus (p < 0.01) and a decrease in peak strain (p < 0.01). In contrast to previous three-bending tests on whole rib and rib cortical bone coupons, there were no significant differences in material properties with respect to rib region or rib level. When these results are considered in conjunction with the previous three-point bending tests, there is regional variation in the structural response of the human rib cage, but this variation appears to be primarily a result of changes in the local geometry of each rib while the material properties remain nearly constant within an individual.
Master of Science

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Pietrzak, Magdalena. "Analysis of strain and stress fields within granular material in active earth pressure state : PhD thesis summary." Rozprawa doktorska, [s.n.], 2013. http://dlibra.tu.koszalin.pl/Content/1082.

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Dong, Xudong. "Stress distribution and failure mode of dental ceramic structures under Hertzian indentation." Hong Kong : University of Hong Kong, 2001. http://sunzi.lib.hku.hk/hkuto/record.jsp?B22989560.

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Santos, André Pereira dos. "Strain effect on the properties of K0.5Na0.5NbO3 films." Master's thesis, Universidade de Aveiro, 2017. http://hdl.handle.net/10773/22592.

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Mestrado em Engenharia de Materiais
Este trabalho é sobre materiais cerâmicos isentos de chumbo destinados a aplicações electromecânicas e candidatos à substituição de electrocerâmicos à base de chumbo. O titanato zirconato de chumbo (PZT) é o cerâmico piezoeléctrico mais utilizado em todo o mundo. No entanto, contém mais de 60 % de chumbo que é um elemento tóxico para os seres humanos e para o ambiente. Em 2003, a União Europeia aprovou uma directiva que proíbe e restringe o uso de elementos potencialmente perigosos, tais como o chumbo. Devido à inexistência de materiais aptos para a substituição do PZT, foi feita uma exceção até ser encontrado um material alternativo competitivo. O niobato de potássio e sódio (KNN), devido à sua elevada temperature de Curie e propriedades piezoeléctricas moderadas, é um dos materiais isentos de chumbo mais promissores para substituição do PZT. No entanto, a sua efetiva adopção industrial requer, entre outros aspectos, a optimização das suas propriedades. A maioria da literatura está focada em materiais cerâmicos densos com base em KNN. Recentemente, os filmes de KNN receberam bastante atenção, pois é uma das alternativas mais promissoras para várias aplicações, como por exemplo, sensores, atuadores, sistemas de colheita de energia e sistemas microelectromecânicos (MEMS). Essa atenção deve-se às altas propriedades piezoelétricas nas suas contrapartidas cerâmicas. No entanto, duas questões principais ainda impedem a fabricação de filmes de KNN de alta qualidade: tensão exercida entre o filme de KNN e o substrato e a perda de óxidos alcalinos durante a sua preparação. Neste contexto, este trabalho tem como objectivo o estudo da influência de tensões existentes nos filmes de KNN nas propriedades elétricas. Para este fim, filmes de KNN com i) 20% de excesso de potássio e sódio e uma concentração molar de 0,4; ii) 20% de excesso de potássio e sódio e concentração molar de 0,2; iii) 5% de potássio com concentração molar de 0,4 e iv) 5% de potássio e concentração molar de 0,2 foram depositados em substratos de Si/SiO2, Al2O3 policristalino, Si/SiO2/TiO2/Pt, Al2O3/Pt e SrTiO3/Pt. Verificou-se que os filmes finos de KNN têm uma estrutura perovskita sem fases secundárias. Os filmes finos de KNN com 20% de excesso de potássio e sódio depositado nos substratos de Al2O3/Pt e SrTiO3/Pt mostram uma orientação preferencial ao longo do pico (100), tendo um fator de Lottering maior que 38% (f100> 38%) Os filmes finos de KNN depositados nos substratos de Si/SiO2/TiO2/Pt encontram-se sob uma tensão de tracção, enquanto que os filmes finos de KNN depositados nos substratos de SrTiO3/Pt e Al2O3/Pt estão sob uma tensão compressiva. Entre os filmes finos de KNN com 20% de excesso de potássio e sódio e concentração de 0,2 M, o filme que apresenta a permitividade mais elevada (ε´ = 585 (10 kHz) with tanδ = 0.182) é filme depositado no subtrato de SrTiO3/Pt e o filme depositado em Si/SiO2/TiO2/Pt é o que apresenta as perdas mais baixas (ε' = 382 (10 kHz) com tanδ = 0,093). O ultimo filme, apresenta valores de polarização remanescente mais elevados (Pr = 9,57 μC/cm2 (a 50 Hz) com Ec = 36 kV/cm). Os filmes finos de KNN com 5% de excesso de potássio com uma concentração molar de 0,2 têm o Pr mais elevado nos filmes depositados nos substratos de SrTiO3/Pt (Pr = 4,55 μC/cm2 (a 50 Hz) com Ec = 34 kV/cm). Os filmes depositados em Al2O3/Pt têm a menor permitividade e polarização moderada, mas são os que mais sustentam altos campos elétricos, mostrando “loops” de histerese quadrados. As imagens de PFM mostram que os filmes finos de KNN com uma concentração molar de 0,4 depositados nos substratos de Al2O3/Pt e SrTiO3/Pt têm domínios bem definidos, com um tamanho médio que varia entre os 75 e os 100 nm, sendo separados por paredes com um domínio de 180o. Para os filmes com uma concentração molar de 0,2, são observados domínios com escala micrométrica e obtidas curvas de histerese piezoeléctricas locais. Os resultados deste estudo contribuem definitivamente para o conhecimento no campo dos materiais piezoelétricos sem chumbo.
This work is about lead-free piezoelectric materials intended for electromechanical and energy harvesting applications. One of the most widely used piezoelectric ceramics is lead zirconate titanate (PZT). However, it contains more than 60% of lead that is toxic for humans and environment. In 2003, a directive from European Union has prohibited the use of potentially hazardous elements as lead. Due to the lack of competitive materials for PZT replacement an exception was created until a competitive alternative be found. Potassium and sodium niobate (KNN) due to its high Curie temperature and moderate piezoelectric properties is currently one of the most promising lead-free materials for PZT substitution. However, its effective industrial adoption requires, among others, optimization of its properties. Most literature is focused on KNN-based bulk materials. Recently, KNN based films have received more attention as one of the promising alternatives in various applications, such as sensors, actuators, energy harvesting systems and microelectromechanical systems (MEMS). This attention is due to the high piezoelectric properties in their bulk counterparts. However, two main issues still inhibit the fabrication of high-quality KNN-based films: stress/strain exerted between the KNN film and the substrate and the loss of alkali oxides during its preparation. In this context, in this work the influence of stress/strain applied to KNN films on the electrical properties is studied. For this purpose, KNN films with i) 20% excess of potassium and sodium and 0.4 M concentration, ii) 20% excess of potassium and sodium and 0.2 M concentration, iii) 5% of potassium and 0.4 M concentration and iv) 5% of potassium and 0.2 M concentration were deposited on: Si/SiO2, polycrystalline Al2O3, Si/SiO2/TiO2/Pt, Al2O3/Pt and SrTiO3/Pt substrates. It was found that KNN thin films have a perovskite structure without secondary phases. KNN thin films with 20% excess of potassium and sodium deposited on Al2O3/Pt and SrTiO3/Pt substrates show a preferential orientation along (100) direction and have Lottering factor higher than 38% (f100 > 38%). KNN thin films deposited on Si/SiO2/TiO2/Pt substrates are found to be under a tensile strain, while the KNN films deposited on SrTiO3/Pt and Al2O3/Pt substrates are under a compressive strain. Among the KNN thin films with 20% excess of potassium and sodium and 0.2 M concentration, the film that show the highest permittivity (ε´ = 585 (10 kHz) with tanδ = 0.182) is that on SrTiO3/Pt, while the one deposited on Si/SiO2/TiO2/Pt substrate possesses the lowest losses (ε´ = 382 (10 kHz) with tanδ = 0.093). The later film shows as well the highest values of remnant polarization (Pr = 9.57 μC/cm2 (at 50 Hz) with Ec = 36 kV/cm). However, the KNN thin films with 5% excess of potassium and 0.2 M concentration that has the highest Pr is the film deposited on SrTiO3/Pt substrates (Pr = 4.55 μC/cm2 (at 50 Hz) with Ec= 34 kV/cm). The films deposited on Al2O3/Pt have the lowest permittivity and moderate polarization, but they are the most sustainable to high electric field, showing square-like hysteresis loops. The PFM images shows that the KNN thin films with 0.4 M concentration deposited on SrTiO3/Pt and Al2O3/Pt substrates have well defined domains with average size between 75 and 100 nm, separated by 180o domain walls. For the films with 0.2 M concentration micrometre scale domains are observed and local piezoelectric loops are obtained. The results of this study definitely contribute to the knowledge in the field of lead-free piezoelectric materials.

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38

Gonzales, Manny. "The mechanochemistry in heterogeneous reactive powder mixtures under high-strain-rate loading and shock compression." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54393.

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This work presents a systematic study of the mechanochemical processes leading to chemical reactions occurring due to effects of high-strain-rate deformation associated with uniaxial strain and uniaxial stress impact loading in highly heterogeneous metal powder-based reactive materials, specifically compacted mixtures of Ti/Al/B powders. This system was selected because of the large exothermic heat of reaction in the Ti+2B reaction, which can support the subsequent Al-combustion reaction. The unique deformation state achievable by such high-pressure loading methods can drive chemical reactions, mediated by microstructure-dependent meso-scale phenomena. Design of the next generation of multifunctional energetic structural materials (MESMs) consisting of metal-metal mixtures requires an understanding of the mechanochemical processes leading to chemical reactions under dynamic loading to properly engineer the materials. The highly heterogeneous and hierarchical microstructures inherent in compacted powder mixtures further complicate understanding of the mechanochemical origins of shock-induced reaction events due to the disparate length and time scales involved. A two-pronged approach is taken where impact experiments in both the uniaxial stress (rod-on-anvil Taylor impact experiments) and uniaxial strain (instrumented parallel-plate gas-gun experiments) load configurations are performed in conjunction with highly-resolved microstructure-based simulations replicating the experimental setup. The simulations capture the bulk response of the powder to the loading, and provide a look at the meso-scale deformation features observed under conditions of uniaxial stress or strain. Experiments under uniaxial stress loading reveal an optimal stoichiometry for Ti+2B mixtures containing up to 50% Al by volume, based on a reduced impact velocity threshold required for impact-induced reaction initiation as evidenced by observation of light emission. Uniaxial strain experiments on the Ti+2B binary mixture show possible expanded states in the powder at pressures greater than 6 GPa, consistent with the Ballotechnic hypothesis for shock-induced chemical reactions. Rise-time dispersive signatures are consistently observed under uniaxial strain loading, indicating complex compaction phenomena, which are reproducible by the meso-scale simulations. The simulations show the prevalence of shear banding and particle agglomeration in the uniaxial stress case, providing a possible rationale for the lower observed reaction threshold. Bulk shock response is captured by the uniaxial strain meso-scale simulations and is compared with PVDF stress gauge and VISAR traces to validate the simulation scheme. The simulations also reveal the meso-mechanical origins of the wave dispersion experimentally recorded by PVDF stress gauges.

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39

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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40

Mathiesen, Danielle Samone. "Experiments, Constitutive Modeling, and Multi-Scale Simulations of Large Strain Thermomechanical Behavior of Poly(methyl methacrylate) (PMMA)." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1415694651.

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41

Katzenberger, Jr Michael J. "Effects of Sex, Strain Rate, and Age on the Tensile and Compressive Material Properties of Human Rib Cortical Bone." Thesis, Virginia Tech, 2019. http://hdl.handle.net/10919/102889.

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The objective of this study was to evaluate the effects of sex, loading rate, and age on the tensile and compressive material properties of human rib cortical bone over a wide range of subject demographics. Tension coupons were tested from sixty-one (n = 61) subjects (M = 32, F = 29) ranging in age from 17 to 99 years of age (Avg. = 56.4 +/- 26.2 yrs.). Compression samples were tested from thirty (n = 30) subjects (M = 19, F = 11) ranging in age from 18 to 95 years of age (Avg. = 49.0 +/- 23.9 yrs.). For each subject, one coupon/sample was tested to failure on a material testing system at a targeted strain rate of 0.005 strain/s, while a second coupon/sample was tested at 0.5 strain/s. A load cell was used to measure axial load for both the tension coupons and compression samples. An extensometer was used to measure displacement within the gage length of the tension coupons and a deflectometer was used to measure displacement of the compression samples. Tension data were obtained from fifty-eight (n = 58) coupons at 0.005 strain/s and fifty-eight (n = 58) coupons at 0.5 strain/s, with fifty-five (n = 55) matched pairs. Compression data were obtained from thirty (n = 30) compression samples at 0.005 strain/s and thirty (n = 30) samples at 0.5 strain/s. The elastic modulus, yield stress, yield strain, ultimate stress, elastic strain energy density (SED), plastic SED, and total SED were then calculated for each tensile and compression test. In addition, failure stress and failure strain were calculated for each tension test. There were no significant differences in the tensile material properties between sexes and no significant interactions between age and sex for either method of loading. In regard to the differences in tensile material properties with respect to loading rate, yield stress, yield strain, failure stress, ultimate stress, elastic SED, plastic SED, and total SED were significantly lower at 0.005 strain/s compared to 0.5 strain/s. All material properties were significantly lower at 0.005 strain/s compared to 0.5 strain/s in compression. Spearman correlation analyses showed that all tensile material properties had significant negative correlations with age at 0.005 strain/s except modulus. At 0.5 strain/s, all tensile material properties except yield strain had significant negative correlations with age. No significant correlations were observed in material properties with respect to advanced age in compression at either loading rate. Although the results revealed that the tensile material properties of human rib cortical bone varied significantly with respect to chronological age, the R2 values only ranged from 0.15 - 0.62, indicating that there may be other underlying variables that better account for the variance within a given population. Overall, this is the first study to analyze the effects of sex, loading rate, and age on tensile material properties of human rib cortical bone using a reasonably large sample size and the first study to test the compressive material properties of human rib cortical bone. The results of this study provide data that allows FEMs to better assess thoracic injury risk for all vehicle occupants. Additionally, this study provides the necessary data to more accurately model and assess differences in the material response of the rib cage for nearly all vehicle occupants of driving age.
Master of Science

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42

Doudican, Bradley M. "Modeling Repair of Fiber Reinforced Polymer Composites Employing a Stress-Based Constitutive Theory and Strain Energy-Based Progressive Damage and Failure Theory." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1373926827.

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43

Bisplinghoff, Jill Aliza. "Biomechanical Response of the Human Eye to Dynamic Loading." Thesis, Virginia Tech, 2009. http://hdl.handle.net/10919/31880.

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Blindness due to ocular trauma is a significant problem in the United States considering that each year approximately 500,000 years of eyesight are lost. The most likely sources of eye injuries include sports related impacts, automobile accidents, consumer products, and military combat. Out of the 1.9 million total eye injuries in the country, more than 600,000 sports injuries occur each year and 40,000 of them require emergency care. In 2007, approximately 66,000 people suffered from vehicle related eye injuries in the United States. Of the vehicle occupants sustaining an eye injury during a crash, as many as 15% to 25% sustained severe eye injuries and it was shown that within these severe eye injuries as many as 45% resulted in globe rupture.

The purpose of this thesis is to characterize the biomechanical response of the human eye to dynamic loading. A number of test series were conducted with different loading conditions to gather data. A drop tower pressurization system was used to dynamically increase intraocular pressure until rupture. Results for rupture pressure, stress and strain were reported. Water streams that varied in diameter and velocity were developed using a customized pressure system to impact eyes. Intraocular pressure, normalized energy and eye injury risk were reported. A Facial and Ocular Countermeasure Safety (FOCUS) headform was used to measure the force applied to a synthetic eye during each hit from projectile shooting toys. The risk of eye injury for each impact was reported. These data provide new and significant research to the field of eye injury biomechanics to further the understanding of eye injury thresholds.
Master of Science

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董旭東 and Xudong Dong. "Stress distribution and failure mode of dental ceramic structures under Hertzian indentation." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2001. http://hub.hku.hk/bib/B31241621.

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Anyanwu, Ezechukwu John. "Low Alloy Steel Susceptibility to Stress Corrosion Cracking in Hydraulic Fracturing Environment." University of Dayton / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1398948610.

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Tsai, Ming-Yi. "Application of localized hybrid methods of stress analysis to some problems in the mechanics of composites." Diss., Virginia Tech, 1990. http://hdl.handle.net/10919/39697.

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47

Åberg, Jonas. "On the Experimental Determination of Damping of Metals and Calculation of Thermal Stresses in Solidifying Shells." Doctoral thesis, KTH, Materialvetenskap, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4038.

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This thesis explores experimentally and theoretically two different aspects of the properties and behaviour of metals: their ability to damp noise and their susceptibility to crack when solidifying. The first part concerns intrinsic material damping, and is motivated by increased demands from society for reductions in noise emissions. It is a material’s inherent ability to reduce its vibration level, and hence noise emission, and transform its kinetic energy into a temperature increase. To design new materials with increased intrinsic material damping, we need to be able to measure it. In this thesis, different methods for measurement of the intrinsic damping have been considered: one using Fourier analysis has been experimentally evaluated, and another using a specimen in uniaxial tension to measure the phase-lag between stress and strain has been improved. Finally, after discarding these methods, a new method has been developed. The new method measures the damping properties during compression using differential calorimetry. A specimen is subjected to a cyclic uniaxial stress to give a prescribed energy input. The difference in temperature between a specimen under stress and a non-stressed reference sample is measured. The experiments are performed in an insulated vacuum container to reduce convective losses. The rate of temperature change, together with the energy input, is used as a measure of the intrinsic material damping in the specimen. The results show a difference in intrinsic material damping, and the way in which it is influenced by the internal structure is discussed. The second part of the thesis examines hot cracks in solidifying shells. Most metals have a brittle region starting in the two-phase temperature range during solidification and for some alloys this region extends as far as hundreds of degrees below the solidus temperature. To calculate the risk of hot cracking, one needs, besides knowledge of the solidifying material’s ability to withstand stress, knowledge of the casting process to be able to calculate the thermal history of the solidification, and from this calculate the stress. In this work, experimental methods to measure and evaluate the energy transfer from the solidifying melt have been developed. The evaluated data has been used as a boundary condition to numerically calculate the solidification process and the evolving stress in the solidifying shell. A solidification model has been implemented using a fixed-domain methodology in a commercial finite element code, Comsol Multiphysics. A new solidification model using an arbitrary Lagrange Eulerian (ALE) formulation has also been implemented to solve the solidification problem for pure metals. This new model explicitly tracks the movement of the liquid/solid interface and is much more effective than the first model.
QC 20100929

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48

Zhalehjoo, Negin. "Characterisation of the deformation behaviour of unbound granular materials using repeated load triaxial testing." Thesis, Federation University of Australia, 2018. http://researchonline.federation.edu.au/vital/access/HandleResolver/1959.17/166953.

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Unbound Granular Materials (UGMs) are used in the base/subbase layers of flexible pavements for the majority of roads around the world. The deterioration of pavements increases with the increase of traffic loadings. To ensure the long-term performance and serviceability of pavement structures through a realistic design, the precise evaluation and comprehensive characterisation of the resilient and permanent deformation behaviour of pavement materials are essential. The present PhD study aims to investigate the characterisation of the resilient and permanent deformation behaviour of four road base UGMs sourced from quarries in Victoria, Australia, using Repeated Load Triaxial (RLT) testing. The triaxial system used in this study is instrumented with four axial deformation measurement transducers to achieve highly precise measurements and to evaluate the effect of instrumentation on the resilient modulus of UGMs. The resilient Poisson’s ratio of the studied UGMs is also determined using a radial Hall-Effect transducer. Moreover, a series of permanent deformation tests is performed to precisely characterise the axial and radial permanent deformation behaviour of UGMs and investigate the factors that may significantly influence the accumulated axial and radial permanent deformations. Finally, three permanent deformation models incorporated with a time-hardening procedure are employed to predict the magnitude of permanent strain for multiple stress levels of the RLT test. The predictions using the employed models are then compared against the measured values to evaluate the suitability of the models and to identify the model that best predicts the strain accumulation behaviour of the tested UGMs. While this study focuses on the resilient and permanent deformation behaviour of four Victorian UGMs under repeated loading, the knowledge generated from this comprehensive investigation will contribute towards the global development of more reliable methods for evaluating the long-term performance of pavement structures and minimising road maintenance and repair costs.
Doctor of Philosophy

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49

Erdil, Baris. "Behavior Of Cfrp Confined Concrete Specimens Under Temperature Cycles And Sustained Loads." Phd thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614137/index.pdf.

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The application of carbon fiber reinforced polymers (CFRP) is one of the effective retrofitting and strengthening methods that is used worldwide and is starting to be used in Turkey as well because they have high strength and high modulus in the fiber direction, have very low coefficient of thermal expansion when compared to concrete and steel and are known not to corrode. Since FRPs are lightweight, their mass can be neglected when compared to concrete and steel. However, before proposing this material as an alternative for strengthening and retrofitting applications their long-term behavior should be understood because they are applied on to concrete by several layers of epoxy-based adhesives, which can be affected by change in humidity, temperature and load. Therefore, behavior of CFRP-strengthened structures in varying temperature and humidity conditions must be investigated. In this dissertation, behavior of CFRP confined cylindrical and prismatic concrete specimens having square cross-section were investigated under sustained compressive loads, dry and wet heating-cooling cycles, and outdoor exposures under direct sunlight, to determine the possible changes in their mechanical properties. Sustained loads were applied as the 40% and 50% of their confined axial load capacity. In addition to the sustained loads, specimens were subjected to 200 heating-cooling cycles between -10°
C to 50°
C. In order to understand the change in behavior of CFRP confined concrete specimens better, they were divided in six groups. A single effect was investigated in each group. After aging tests mechanical properties of the specimens were recorded via monotonic uniaxial loading. It was observed that temperature cycles had little effect on behavior but sustained loads changed the shape of the axial stress-strain diagram and resulted in a dramatic decrease in ultimate strain. Based on the test results and also using the data of similar studies available in the literature, strength and strain models considering the exposures as independent parameters were established and finally axial stress-strain curve was tried to be predicted.

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50

Harrison, Peter Newton. "Interlaminar stress analysis of dropped-ply laminated plates and shells by a mixed method." Diss., Virginia Tech, 1994. http://hdl.handle.net/10919/39735.

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A mixed method of approximation based on Reissner's variational principle is developed for the linear analysis of interlaminar stresses in laminated composites, with special interest in laminates that contain terminated internal plies (dropped-ply laminates). Two models are derived, one for problems of generalized plane deformation and the other for the axisymmetric response of shells of revolution. A layerwise approach is taken in which the stress field is assumed with an explicit dependence on the thickness coordinate in each layer. The dependence of the stress field on the thickness coordinate is determined such that the three-dimensional equilibrium equations are satisfied by the approximation. The solution domain is reduced to one dimension by integration through the thickness. Continuity of tractions and displacements between layers is imposed. The governing two-point boundary value problem is composed of a system of both differential and algebraic equations (DAEs) and their associated boundary conditions. Careful evaluation of the system of DAEs was required to arrive at a form that allowed application of a one-step finite difference approximation. A two-stage Gauss implicit Runge-Kutta finite difference scheme was used for the solution because of its relatively high degree of accuracy. Patch tests of the two models revealed problems with solution accuracy for the axisymmetric model of a cylindrical shell loaded by internal pressure. Parametric studies of dropped-ply laminate characteristics and their influence on the interlaminar stresses were performed using the generalized plane deformation model Eccentricity of the middle surface of the laminate through the ply drop-off was found to have a minimal effect on the interlaminar stresses under longitudinal compression, transverse tension, and in-plane shear. A second study found the stiffness change across the ply termination to have a much greater influence on the interlaminar stresses. Correlations between the stiffness ratio of the thick to the thin sections of the laminates and the magnitude of a parameter based on a quadratic delamination criterion were found to be surprisingly good for longitudinal compression and in-plane shear loadings. For laminates with very stiff terminated plies loaded in longitudinal compression, inclusion of a short insert of softer composite material at the end of the dropped plies was found to significantly reduce the interlaminar stresses produced.
Ph. D.

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Dissertations / Theses on the topic 'Stress and Strain (Materials)'

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