Dissertations / Theses on the topic 'Thermal properties; mechanical properties'
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1
Cohen, Ellann. "Thermal properties of advanced aerogel insulation." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/67795.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 74-76).
Buildings consume too much energy. For example, 16.6% of all the energy used in the United States goes towards just the heating and cooling of buildings. Many governments, organizations, and companies are setting very ambitious goals to reduce their energy use over the next few years. Because the time periods for these goals are much less than the average lifetime of a building, existing buildings will need to be retrofitted. There are two different types of retrofitting: shallow and deep. Shallow retrofits involve the quickest and least expensive improvements often including reducing infiltration around windows, under doors, etc and blowing more insulation into the attic. Deep retrofits are those that involve costly renovation and typically include adding insulation to the walls and replacing windows. A new, easily installable, inexpensive, and thin insulation would move insulating the walls from the deep retrofit category to the shallow retrofit category and thus would revolutionize the process of retrofitting homes to make them more energy efficient. This thesis provides an overview of a concept for a new, easily installable, inexpensive, thin aerogel-based insulation and goes into detail on how the thermal properties of the aerogel were measured and validated. The transient hot-wire method for measuring the thermal conductivity of very low thermal conductivity silica aerogel (1 0mW/m K at 1 atm) along with a correction for end effects was validated with the NIST (National Institute of Standards and Technology) Standard Reference Material 1459, fumed silica board to within 1 mW/mK. Despite the translucence of the aerogel at certain wavelengths, radiation is not an issue through the aerogel during the hot-wire test but may be an issue in actual use as an insulation. The monolithic aerogel thermal conductivity drops significantly with slightly reduced pressure (3.2 mW/m K at 0.1atm). For the final composite insulation, the new silica aerogel formula is a great choice and it is recommended to reduce the pressure around the aerogel to 1 / 1 0 th. In the future, a prototype of an insulation panel combining a 3-D truss structure, monolithic or granular silica aerogel, and reduced pressure will be constructed and tested.
by Ellann Cohen.
S.M.
2
Skow, Erik (Erik Dean). "Processing and thermal properties of molecularly oriented polymers." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/40368.
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Thesis (S.M. in Mechanical Engineering and Naval Architecture and Marine Engineering)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.Includes bibliographical references (p. 61-63).
High molecular weight polymers that are linear in molecular construction can be oriented such that some of their physical properties in the oriented direction are enhanced. For over 50 years polymer orientation and processing has been extensively studied to improve the mechanical properties of polymers. In more recent history the anisotropic thermal properties of oriented polymers have been studied. This thesis investigates the thermal properties of Ultra High Molecular Weight Polyethylene (UHMW-PE) and explores applications for the same. This thesis details an effective means of aligning the molecules in bulk polyethylene sheets through stretching in the gel state. Tests have shown that bulk UHMW-PE can be stretched 50-80 times in xylene. The thermal conductivity of bulk UHMW-PE is 0.3 W/mK, while that of a sample stretched 20-25 times is over 4.5 W/mK.
by Erik Skow.
S.M.in Mechanical Engineering and Naval Architecture and Marine Engineering
3
Curran, J. A. "Thermal and mechanical properties of plasma electrolytic oxide coatings." Thesis, University of Cambridge, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.598226.
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A critical review of the current knowledge of PEO coating characteristics and properties is made, and several areas requiring more accurate or more detailed investigations are identified. A leading commercial product – the KeroniteTM coating for aluminium alloys – is the used as a basis for the investigation of the microstructure and properties of PEO coatings. Coating structure and morphology are studied quantitatively to investigate their growth mechanism. Composition is accurately determined for the first time, allowing predictions of physical, mechanical and thermal properties to be made. Particular attention is also paid to the presence of amorphous material and fine-scale porosity – properties which had previously been neglected. The latter is critical to the understanding of coating formation and the capacity for coating impregnation, and is measured and characterised using numerous porosimetry techniques. Mechanical properties of the coatings are characterised using indentation and macroscopic techniques such as beam bending. Correlations are established between the observed structure and measured physical properties such as hardness, local modulus and global stiffness. It is found that wear resistance can also be explained on the basis of the measured mechanical properties and structure. The discovery of low coating stiffness means that high-temperature applications, which had previously been dismissed on the basis of thermal expansion mismatch between the coating and substrate, may indeed be possible. The thermal stability of the coatings is therefore investigated and their stability up to 800°C is demonstrated. Residual stresses are measured and explained in terms of the postulated coating growth mechanism.
4
Johnson, Jeremy A. (Jeremy Andrew). "Optical characterization of complex mechanical and thermal transport properties." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/68543.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2011.Page 176 blank. Cataloged from PDF version of thesis.
Includes bibliographical references (p. 163-175).
Time-resolved impulsive stimulated light scattering (ISS), also known as transient grating spectroscopy, was used to investigate phonon mediated thermal transport in semiconductors and mechanical degrees of freedom linked to structural relaxation in supercooled liquids. In ISS measurements, short optical pulses are crossed to produce a periodic excitation profile in or at the surface of the sample. Light from a probe beam that diffracts off the periodic material response is monitored to observe the dynamics of interest. A number of improvements were put into practice including the ability to separate so-called amplitude and phase grating signal contributions using heterodyne detection. This allowed the measurement of thermal transport in lead telluride and gallium arsenide-aluminum arsenide superlattices, and also provided the first direct observation of the initial crossover from diffusive to ballistic thermal transport in single crystal silicon and gallium arsenide at room temperature. Recent first-principles calculations of the thermal conductivity accumulation as a function of phonon mean free path allowed direct comparison to our measured results. In an effort to test theoretical predictions of the prevailing first principles theory of the glass transition, the mode coupling theory (MCT), photoacoustic measurements throughout much of the MHz acoustic frequency range were conducted in supercooled liquids. Longitudinal and shear acoustic waves were generated and monitored in supercooled liquid triphenyl phosphite in order to compare the dynamics. An additional interferometric technique analogous to ISS was developed to probe longitudinal acoustic waves at lower frequencies than was typically accessible with ISS. Lower frequency acoustic data were collected in supercooled tetramethyl tetraphenyl trisiloxane in conjunction with piezotransducer, ISS, and picosecond ultrasonics measurements to produce the first truly broadband mechanical spectra of a viscoelastic material covering frequencies continuously from mHz to hundreds of GHz. This allowed direct testing of the MCT predicted connection between fast and slow relaxation in supercooled liquids. Measurements of the quasi-longitudinal speed of sound in the energetic material cyclotrimethylene trinitramine (RDX) were also performed with ISS and picosecond ultrasonics from 0.5 to 15 GHz in order to resolve discrepancies in published low and high frequency elastic constants.
by Jeremy A. Johnson.
Ph.D.
5
Wain, Susan Elizabeth. "Thermal and mechanical properties of pulverised fuel boiler slags." Thesis, Imperial College London, 1991. http://hdl.handle.net/10044/1/8209.
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Hovell, Ian. "Dynamic mechanical thermal properties of moulded poly(vinylchloride) swollen with organic liquids." Thesis, Loughborough University, 1987. https://dspace.lboro.ac.uk/2134/33149.
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Compression-moulded unplasticised poly(vinylchloride) (uPVC) was swollen with various organic liquids at two temperatures, 60°C and 30°C, both temperatures being below the glass transition temperature of uPVC. Liquids were chosen to give a range of solubility parameters, molecular sizes and ability to form hydrogen bonds. It was hoped to find a PVC–liquid system which behaved similarly to PVC swollen with vinyl chloride monomer (VCM).
7
Othuman, Mydin Md Azree. "Lightweight foamed concrete (LFC) thermal and mechanical properties at elevated temperatures and its application to composite walling system." Thesis, University of Manchester, 2010. https://www.research.manchester.ac.uk/portal/en/theses/lightweight-foamed-concrete-lfc-thermal-and-mechanical-properties-at-elevated-temperatures-and-its-application-to-composite-walling-system(5a13ec7f-d460-4354-a296-6d1ffecff971).html.
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LFC is cementatious material integrated with mechanically entrained foam in the mortar slurry which can produce a variety of densities ranging from 400 to 1600 kg/m3. The application of LFC has been primarily as a filler material in civil engineering works. This research explores the potential of using LFC in building construction, as non-load-bearing partitions of lightweight load-bearing structural members. Experimental and analytical studies will be undertaken to develop quantification models to obtain thermal and mechanical properties of LFC at ambient and elevated temperatures. In order to develop thermal property model, LFC is treated as a porous material and the effects of radiant heat transfer within the pores are included. The thermal conductivity model results are in very good agreement with the experimental results obtained from the guarded hot plate tests and with inverse analysis of LFC slabs heated from one side. Extensive compression and bending tests at elevated temperatures were performed for LFC densities of 650 and 1000 kg/m3 to obtain the mechanical properties of unstressed LFC. The test results indicate that the porosity of LFC is mainly a function of density and changes little at different temperatures. The reduction in strength and stiffness of LFC at high temperatures can be predicted using the mechanical property models for normal weight concrete provided that the LFC is based on ordinary Portland cement. Although LFC mechanical properties are low in comparison to normal weight concrete, LFC may be used as partition or light load-bearing walls in a low rise residential construction. To confirm this, structural tests were performed on a composite walling system consisting of two outer skins of profiled thin-walled steel sheeting with LFC core under axial compression, for steel sheeting thicknesses of 0.4mm and 0.8mm correspondingly. Using these test results, analytical models are developed to calculate the maximum load-bearing capacity of the composite walling, taking into consideration the local buckling effect of the steel sheeting and profiled shape of the LFC core. The results of a preliminary feasibility study indicate that LFC can achieve very good thermal insulation performance for fire resistance. A single layer of 650 kg/m3 density LFC panel of about 21 mm would be able to attain 30 minutes of standard fire resistance rating, which is comparable to gypsum plasterboard. The results of a feasibility study on structural performance of a composite walling system indicates that the proposed panel system, using 100mm LFC core and 0.4mm steel sheeting, has sufficient load carrying capacity to be used in low-rise residential construction up to four-storeys.
8
Kulamarva, Arun. "Rheological and thermal properties of sorghum dough." Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=98740.
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Sorghum is a gluten free cereal and forms the staple diet of a majority of the populations living in the semi-arid tropics dough. It is usually consumed in the form of bread made from the grain flour. Dough made with sorghum flour has poor viscoelastic properties compared to wheat dough and mechanical methods for production of sorghum roti are scarce. This study was conducted to elucidate the rheological and thermal properties of sorghum dough to establish its behavior. The temperature and amount of water used for preparation of the dough and the composition of the flour were varied. Wheat, soya and black gram flours were used to prepare the composite doughs. Sensory characteristics of roti made with these dough samples by the traditional method and mechanical compression were studied. The results are presented and their implications are discussed.
9
Dames, Christopher Eric. "Thermal properties of nanowires and nanotubes : modeling and experiments." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/38259.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.Includes bibliographical references.
Nanowires and nanotubes have drawn a great deal of recent attention for such potential applications as lasers, transistors, biosensors, and thermoelectric energy converters. Although the thermal properties of nanowires can differ greatly from their bulk counterparts, the theoretical and experimental understanding of these differences is still limited. Thermal performance is especially important for nanowire thermoelectrics, which are expected to have energy conversion efficiencies far superior to bulk materials. This efficiency increase may lead to a broad range of applications for reliable, solid-state energy conversion, including household refrigeration and waste heat scavenging for power generation. In this thesis, the fundamental thermal properties of nanowires and nanotubes are explored from both theoretical and experimental perspectives. Modeling and experiments on titanium dioxide nanotubes confirm that quantum size effects can cause enhancements in the specific heat at low temperature, while modeling of classical size effects in nanowires and superlattice nanowires shows that the thermal conductivity can be reduced by several orders of magnitude compared to bulk, in agreement with available experimental data.
(cont.) To facilitate further experimental studies of individual nanowires, the "3-omega" methods for thermal properties measurements were made more rigorous, simpler to implement, and generalized to 1-omega and 2-omega methods which may be advantageous for nanoscale systems. These methods are used to deduce the thermal properties of a system from its electrical response at the first, second, or third harmonic of a driving current. Finally, a detailed design and preliminary measurements are presented for a new type of hot-wire probe based on Wollaston wire and used to measure the thermoelectric properties of individual nanowires and nanotubes inside a transmission electron microscope.
by Christopher Eric Dames.
Ph.D.
10
Aksel, Cemail. "Thermal shock behaviour and mechanical properties of magnesia-spinel composites." Thesis, University of Leeds, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.275609.
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Barlow, Lyndsey J. "Thermal, mechanical and electrical properties of liquid crystalline polymer electrolytes." Thesis, University of Aberdeen, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.401497.
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It is generally accepted that ion transport in polymer electrolytes is strongly coupled to the local viscosity of the host polymer and that, in most cases, appreciable ionic conductivity below the glass transition temperature is not observed. Recent literature suggests that this may not always be the case and examples of polymer electrolytes exhibiting ionic conductivity decoupled from the polymeric motions have been reported. This thesis investigates one such system, a liquid crystalline polymer electrolyte, which has been reported to show measurable conductivity in the sold phase. The aim is to investigate such decoupled behaviour, how it may be optimised and to understand the conductivity mechanism. The thermal, mechanical and electrical properties of lithium perchlorate and lithium triflate complexes of a liquid crystalline polymer and its non-liquid crystalline analogue have been investigated. These studies suggest that the conductivity is not in fact decoupled from the local motions of the polymer. Selected complexes are then examined further and conductivities measured under variable pressure. From these data, activation energies, volumes and decoupling constants are calculated. These results show that, although not fully coupled, these complexes cannot be considered to exhibit decoupled conductivity and, in fact, the non-liquid crystalline electrolytes actually show a greater tendency towards decoupled behaviour than their liquid crystalline counterparts. In the final chapter, the two polymers are complexed with lithium trifluoromethanesulphonyl imide, a salt that has been reported to give enhanced conducivities. It is found that using this salt does indeed raise conductivities, but also reduces tendencies towards decoupled behaviour.
12
Kamani, Sandeep Kumar. "Influence of defects on thermal and mechanical properties of metals." [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-2901.
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Cerezo, Frances Therese, and francestherese_cerezo@hotmail com. "Thermal stability and mechanical property of polymer layered graphite oxide composites." RMIT University. Applied Sciences, 2006. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20080627.161157.
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Polymer composites formed from layered fillers with high surface volume ratio show enhanced reinforcement. Graphite oxide is a high modulus material that can be separated into thin layers with high surface area. The aim of this study is to prepare polymer layered graphite oxide composites using functionalised polyolefin to enhance compatibility with various forms of layered graphite oxide in varying concentration. Functionalised polyolefins reinforced with layered graphite oxides and expanded graphite oxides were prepared using solution blending and melt blending methods. Three different mixing methods with varying shear intensity were employed to prepare polymer layered graphite oxide composites. The crystalline structure, thermal and mechanical properties of the prepared polymer layered graphite oxide composites was studied. Oxidised graphite prepared from the Staudenmaier method and its exfoliated form were dispersed in poly(ethylene-co-methyl acrylate-co-acrylic acid) (EMAA) via solution blending to prepare EMAA layered composites. The thermal stability was determined using thermogravimetric analysis. The EMAA layered composites showed higher thermal stability in comparison with pure EMAA. The mechanical properties of these EMAA layered composites were determined through dynamic mechanical analysis. Shear modulus, yield stress and storage modulus of EMAA in the presence of graphite oxide fillers decreased. A solution blending method was used to prepare poly(propylene-grafted-maleic anhydride) layered expanded graphite oxide composites (PPMA-EGO). Two types of PPMA-EGO were prepared using different mixing methods - low and high shear were employed. The effects of preparative mixing methods on the PPMA-EGO properties were investigated. The mechanical properties of PPMA-EGO obtained from dynamic mechanical analysis indicated that EGO had a reinforcing effect on the elastic behaviour of PPMA-EGO. This is due to strong interfacial adhesion between PPMA and EGO as a result of hydrogen bonding. The elastic behaviour of PPMA-EGO was affected by the surface area of graphite flakes. Low sheared PPMA-EGO elastic behaviour was found to be higher compared with that of high sheared PPMA-EGO. A melt blending method was used to prepare PPMA-EGO with varying EGO concentration. The interconnected network structure of EGO in the PPMA-EGO was not observed as shown by its scanning electron microscopy images. Thermogravimetric analysis of PPMA-EGO indicates increased decomposition temperature of the PPMA matrix. Dynamic mechanical analysis showed enhanced storage modulus of PPMA-EGO. The maximum elastic modulus of PPMA-EGO was observed at 3 %wt of EGO. The electrical conductivity of PPMA-EGO was measured only for EGO concentrations above 2 %wt. The EGO concentration was found to be the most critical factor in the enhancement of the electrical conductivity of PPMA-EGO. Wide angle X-ray diffraction analysis of all polymer layered graphite oxide composites revealed no change in interlayer spacing of graphite layers, indicating the absence of EMAA intercalation in the graphite layers. The crystallisation temperature and crystallinity of all polymer layered graphite oxide composites were determined using differential scanning calorimetry. The results indicated that graphite oxide and expanded graphite oxides acted as nucleating agents in inducing the crystallisation of functionalised polyolefin in the layered composites. However, the degree of crystallinity of functionalised polyolefin decreased in the layered composites.
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El-Khoja, Amal M. N. "Mechanical, thermal and acoustic properties of rubberised concrete incorporating nano silica." Thesis, University of Bradford, 2019. http://hdl.handle.net/10454/18351.
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Very limited research studies have been conducted to examine the behaviour
of rubberised concrete (RuC) with nano silica (NS) and addressed the acoustic
benefits of rubberised concrete. The current research investigates the effect of
incorporating colloidal nano silica on the mechanical, thermal and acoustic
properties of Rubberised concrete and compares them with normal concrete
(NC).
Two sizes of rubber were used RA (0.5 – 1.5 mm) and RB (1.5 – 3 mm). Fine
aggregate was replaced with rubber at a ratio of 0%, 10%, 20% and 30% by
volume, and NS is used as partial cement replacement by 0%, 1.5% and 3%.
A constant water to cement ratio of 0.45 was used in all concrete mixes.
Various properties of rubberised concrete, including the density, water
absorption, the compressive strength, the flexural strength, splitting tensile
strength and the drying shrinkage of samples was studied as well as thermal and acoustic properties.
Experimental results of compressive strength obtained from this study together
with collected comprehensive database from different sources available in the
literature were compared to five existing models, namely Khatib and Bayomy- 99 model, Guneyisi-04 model, Khaloo-08 model, Youssf-16 model, and
Bompa-17 model. To assess the quality of predictive models, influence of
rubber content on the compressive strength is studied. An artificial neural
network (ANN) models were developed to predict compressive strength of
RuC using the same data used in the existing models. Three ANN sets namely
ANN1, ANN2 and ANN3 with different numbers of hidden layer neurons were
constructed. Comparison between the results given by the ANN2 model and
the results obtained by the five existing predicted models were presented. A
finite element approach is proposed for calculating the transmission loss of
concrete, the displacement in the solid phase and the pressure in the fluid
phase is investigated. The transmission loss of the 50mm concrete samples is
calculated via the COMSOL environment, the results from the simulation show
good agreement with the measured data.
The results showed that, using up to 20% of rubber as fine aggregate with the
addition of 3% NS can produce a higher compressive strength than the NC.
Experimental results of this research indicate that incorporating nano silica into
RuC mixes enhance sound absorption and thermal conductivity compared to
normal concrete (NC) and rubberised concrete without nano silica. This work
suggests that it is possible to design and manufacture concrete which can
provide an improvement to conventional concrete in terms of the attained
vibro-acoustic and thermal performance.Libyan Ministry of Higher Education
15
Deshpande, Girish Nilkanth. "Effect of polysiloxane side groups on chemistry and kinetics of degradation and evolution of pores in the resultant polymer." Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/11845.
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Gauthier, Sylvie 1955. "Synthesis and physical properties of styrene-vinylpyridinium ionomers of various architectures." Thesis, McGill University, 1985. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=72029.
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Styrene-4-vinylpyridinium ionomers of different architectures, random and ABA blocks, were synthesized and their thermal and dynamic mechanical properties investigated.The Tg's of the random ionomers were found to increase regularly with increasing ion content, at a rate of about 3.5(DEGREES)C per mole % of ions. In contrast with other ionomeric systems studied before, however, these materials showed only one peak in their tan delta curves, associated with the Tg of the matrix. The absence of a second, high temperature peak suggests the absence of clusters in these vinylpyridinium ionomers, at least at temperatures above their Tg. The storage modulus curves were in agreement with this conclusion.
An elaborate polymerization line was constructed for the production of the block copolymers by living anionic polymerization; a basic design was modified considerably and two new units were completely designed in this laboratory. Only one Tg, associated with the Tg of the polystyrene phase, was observed in DSC measurements for the resulting ionomers. The glass transition of the ionic domains was detected in dynamic mechanical measurements as a shoulder on the low temperature side of the polystyrene transition. This unexpected low value for the Tg of the ionic domains was attributed to plasticization by water.
17
Bailey, Jacob (Jacob S. ). "Experimental determination of the thermal properties of multi-layered surfaces." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/83683.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (page 23).
This paper outlines a project which aims to use Certified Reduced Basis and General Empirical Interpolation Methods to conduct rapid, inexpensive, computationally simple thermal property estimation for the purpose of material identification. In this specific case, thermal conductivity and diffusivity were the parameters of interest. Towards this end, an experimental apparatus was constructed which applied a thermal load to various materials and observed their thermal responses. Bugs in the experimental apparatus were compensated for by way of a MATLAB script, until the data produced by individual tests became highly repeatable. Software was developed which simulated these thermal responses for given thermal loads and "true" parameter values. The materials were put through multiple tests (Laser Flash Test, Transient Plane Source) to independently identify possible values for these thermal properties. The "true" values were then chosen from these possible values based on how well they allowed the simulated response to fit the measured response. It was found that implementation of the CRB and GEIM allowed for an accurate estimate of these "true values," and did so without exhaustively carrying out a finite element analysis for every possible combination of parameters, creating an exponential increase in performance.
by Jacob Bailey.
S.B.
18
Yun, Tae Sup. "Mechanical and Thermal Study of Hydrate Bearing Sediments." Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7247.
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Gas hydrate is a naturally occurring crystalline compound formed by water molecules and encapsulated gas molecules. The interest in gas hydrate reflects scientific, energy and safety concerns - climate change, future energy resources and seafloor stability. Gas hydrates form in the pore space of sediments, under high pressure and low temperature conditions. This research focuses on the fundamental understanding of hydrate bearing sediments, with emphasis on mechanical behavior, thermal properties and lens formation. Load-induced cementation and decementation effects are explored with lightly cemented loose and dense soil specimens subjected to ko-loading; the small-strain stiffness evolution inferred from shear wave velocity measurement denounces stiffness loss prior to structural collapse upon loading. Systematic triaxial tests address the intermediate and large strain response of hydrate bearing sediments for different mean particle size, applied pressure and hydrate concentration in the pore space; hydrate concentration determines elastic stiffness and undrained strength when Shyd>45%. A unique sequence of particle-level and macro-scale experiments provide new insight into the role of interparticle contact area, coordination number and pore fluid on heat transfer in particulate materials. Micro-mechanisms and necessary boundary conditions are experimentally analyzed to gain an enhanced understanding of hydrate lens formation in sediments; high specific surface soils and tensile stress fields facilitate lens formation. Finally, a new instrumented high-pressure chamber is designed, constructed and field tested. It permits measuring the mechanical and electrical properties of methane hydrate bearing sediments recovered from pressure cores without losing in situ pressure (~20MPa).
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Rummel, Nicholas J. "Dynamic mechanical analysis of magnetic tapes at ultra-low frequencies." Scholarly Commons, 2011. https://scholarlycommons.pacific.edu/uop_etds/773.
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The purpose of this thesis is to investigate the correlated effects of temperature and frequency on the viscoelastic behavior of magnetic tapes, using a custom, ultra-low frequency, dynamic mechanical analyzer. The long-term mechanical and thermal properties of magnetic tapes can be simulated using high temperature and low frequency dynamic mechanical analysis (DMA) experiments. These experiments investigate how the viscoelastic characteristics of tape samples influence the extent to which the tape deforms. The experiments and analyses implemented in this paper examine the influence of the molecular structure on the viscoelasticity of magnetic tapes. Experiments were performed on a variety of magnetic tapes, including poly( ethylene terephthalatc) (PET), poly( ethylene naphthalate) (PEN), metallized poly( ethylene terephthalate) (MPET), and metallized Spaltan (M-SPA). To determine characteristic relating to the magnetic tape substrates, additional experiments examined PEN and PET substrates by removing the front and back magnetic layers from the tape sample. Due to the viscoelastic behavior of the tapes, a time delay was present between the strain and stress signals, which was determined using a Fourier transform program. The elastic modulus (E), storage modulus (E'), loss modulus (E"), and loss tangent (tan 8) were obtained from the time delay for each of the DMA experiments
20
Weisenberger, Matthew Collins. "APPLICATIONS OF MULTIWALL CARBON NANOTUBE COMPOSITES: MECHANICAL, ELECTRICAL AND THERMAL PROPERTIES." Lexington, Ky. : [University of Kentucky Libraries], 2007. http://hdl.handle.net/10225/738.
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Thesis (Ph. D.)--University of Kentucky, 2007.Title from document title page (viewed on March 24, 2008). Document formatted into pages; contains: ix, 97 p. : ill. (some col.). Includes abstract and vita. Includes bibliographical references (p. 91-95).
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Ghazinezami, Ali. "Fire retardancy, thermal stability and mechanical properties of polymeric based nanocomposites." Thesis, Wichita State University, 2013. http://hdl.handle.net/10057/10631.
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Polymeric materials have a wide variety of applications in many manufacturing industries. However, because of the molecular structures and chemical compositions of polymeric materials, they have considerably low resistances against fire or heat. Although these materials are highly flammable, their flame retardancy can be improved significantly by incorporating the flame retardant nanomaterials. Nanoclay, nanotalc and graphene are some of the examples of the flame retardant nanomaterials. These are highly cost effective and environmentally friendly for these applications. These inclusions have a great potential to improve thermal, electrical, and mechanical properties of the new materials. This study is mainly focused on the effects of nanoparticle additions in the polyvinyl chloride (PVC) in terms of the flame retardancy. Five sets of nanocomposite materials were prepared using the solvent casting method at different weight percentages of the nanomaterials. The flame retardancy values of the resultant nanocomposite samples were determined using the ASTM UL 94 standard tests. The results of the experiment were also supported by the thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Surface characterization of the resultant materials was carried out using scanning electron microscopy (SEM), while mechanical properties were determined through a tensile test method. Test results showed that the flame retardancy values of the new nanostructured materials were significantly enhanced in the presence of nanoscale inclusions, which may be useful for various industrial applications. This study may open up new possibilities of using many nanoscale inclusions in various polymers as flame retardant materials for different industrial applications.Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Mechanical Engineering
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O'Reilly, Michael Patrick. "Mechanical properties of granular materials for use in thermal energy stores." Thesis, University of Nottingham, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.353925.
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Deszczynski, Marcin. "Effects of sugars on the mechanical and thermal properties of biopolymers." Thesis, University of Nottingham, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.289482.
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Pan, Deng. "Mechanical properties of diffusion aluminide bond coats for thermal barrier coatings." Available to US Hopkins community, 2003. http://wwwlib.umi.com/dissertations/dlnow/3080741.
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Plunkett, Richard. "Assessment of residual composite properties as influenced by thermal mechanical aging." Thesis, This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-11072008-063142/.
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Thompson, Ian. "Mechanical properties in liquid environments and thermal shock resistance of aluminas." Thesis, Imperial College London, 1989. http://hdl.handle.net/10044/1/47686.
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Shin, Hyun Doug. "Expanding ultrafast photoacoustics for investigation of mechanical properties and thermal transport." Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/122716.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 2019Cataloged from PDF version of thesis.
Includes bibliographical references (pages 123-135).
To address the need for broadband mechanical spectroscopy, femtosecond laser pulses were used to generate and detect acoustic waves. To expand the acoustic phonon frequency bandwidth and range, a thin metal film, a strongly magnetostrictive galfenol film, and strained piezoelectric InGaN/GaN multiple quantum wells were used as transducers. Acoustic wave detection methods included monitoring of optical transmittance/ reflectance, polarization, and diffraction over time. A magnetostrictive material galfenol (Fe₁₋[subscript x] Ga[subscript x]) with 80 percent iron and 20 percent gallium was used as an acoustic transducer using demagnetostriction effect. Galfenol showed great potential as an optimal transducer for the ultrafast magnetostriction in both longitudinal and shear modes. Strained piezoelectric InGaN/GaN semiconductor superlattices were used to generate and to study longitudinal THz acoustic phonons in GaN based structures. During the investigation of the lifetime of up to a 1.4 THz frequency acoustic phonons, specular reflection from an air/GaN free surface was observed. The photo-excitation of THz acoustic phonons in layered structures was introduced as an effective noninvasive tool to investigate the integrity of the fabrication process. This study opened many possibilities for studying mechanical properties and thermal phonons. Next, thermal conductivity reduction due to carrier-phonon interactions was presented. Phonon contributions are critical in heat transport in semiconductors and insulators. To isolate the carrier contributions to the scattering events, photo-excited carriers were generated in silicon through pulsed laser excitation. To measure thermal conductivity changes, time-domain thermoreflectance and transient thermal grating techniques were employed with a, carefully timed additional excitation pulse for carrier generation.
by Hyun Doug Shin.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Chemistry
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Zhao, Yang. "Evaluation and characterisation of thermal barrier coatings." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/evaluation-and-characterisation-of-thermal-barrier-coatings(b6b8d5ef-0cd3-4257-9563-6a6b1626cb49).html.
Full textAbstract:
Evaluation and characterisation of thermal barrier coatings (TBCs) have been conducted correlating microstructure with physical and mechanical properties, to further understand TBC failure mechanisms and performances in this thesis. A modified four-point bending test was employed to investigate the interfacial toughness of atmospheric plasma sprayed TBCs. The delamination of the TBCs occurred mainly within the topcoat. The energy release rate increased from ~50 J/m-2 for as-sprayed conditions to ~120 J/m-2 after annealing at 1150 ºC for 200 hours with a loading phase angle about 42º. Micro X-ray tomography revealed how various types of imperfections developed near the interface and the 3D interface was characterised. Stress measurements by photoluminescence piezospectroscopy (PLPS) and analytical solutions were combined to investigate the local stress around spherically symmetrical portions of a TGO layer formed on Fecralloy. Spherical indenters were used to create curvature with different curvature radii and depths on alloys. The effect of curvature radius on stress was found to be more significant than the depth of local curved area. TGO stress as a function of oxidation time at the curved areas was also discussed. Electron beam physical vapour deposited (EBPVD) TBCs with a β-(Ni,Pt)Al bond coat on CMSX4 substrate were investigated by micro X-ray computed tomography (XCT). The 3D microstructures evolution and damage accumulation were studied. 3D interfacial roughness was calculated and compared to scanning electron microscope image analysis. The calculated interfacial roughness did not change much even after 200 thermal cycles, indicating there was not obvious rumpling in this TBCs sample. Commercial simple and Pt-modified aluminide coatings were studied and compared. Both coatings consisted mainly of β-NiAl phase. Thermogravimetric analysis (TGA) tests indicated that the Pt-modified aluminide coating was much more resistive for oxidation than simple aluminide coating. Instrumented indentation was used to measure the mechanical properties, showing the coatings had similar young’s modulus around 130 GPa while Pt-modified aluminide coating was more ductile and had a higher fracture toughness than simple aluminide coating. The Raman spectra of yttria-stabilised zirconia (YSZ) in the temperature range of 25-1100 ºC were investigated. The peak shift and broadening were carefully analysed. The thermal mismatch stress was found to have a negligible effect on the Raman shift. The dependence can be used to monitor the temperature in YSZ without contact.
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Manisha. "Evaluation of thermal stresses in planar solid oxide fuel cells as a function of thermo-mechanical properties of component materials." Texas A&M University, 2008. http://hdl.handle.net/1969.1/86039.
Full textAbstract:
Fuel cells are the direct energy conversion devices which convert the chemical energy of a
fuel to electrical energy with much greater efficiency than conventional devices. Solid Oxide
Fuel Cell (SOFC) is one of the various types of available fuel cells; wherein the major
components are made of inherently brittle ceramics. Planar SOFC have the advantages of
high power density and design flexibility over its counterpart tubular configuration.
However, structural integrity, mechanical reliability, and durability are of great concern for
commercial applications of these cells. The stress distribution in a cell is a function of
geometry of fuel cell, temperature distribution, external mechanical loading and a mismatch
of thermo-mechanical properties of the materials in contact. The mismatch of coefficient of
thermal expansion and elastic moduli of the materials in direct contact results in the
evolution of thermal stresses in the positive electrode/electrolyte/negative electrode (PEN)
assembly during manufacturing and operating conditions (repeated start up and shut down
steps) as well. It has long been realized and demonstrated that the durability and reliability of
SOFCs is not only determined by the degradation in electrochemical performance but also
by the ability of its component materials to withstand the thermal stresses.
In the present work, an attempt has been made to evaluate the thermal stresses as a function
of thermal and mechanical properties of the component materials assuming contribution
from other factors such as thermal gradient, mechanical loading and in-service loading
conditions is insignificant. Materials used in the present study include the state of art anode (Ni-YSZ), electrolyte(YSZ) and cathode materials(LM and LSM) of high temperature SOFC
and also the ones being suggested for intermediate temperature SOFC Ni-SCZ as an anode,
GDC and SCZ as electrolyte and LSCF as the cathode. Variation of thermo-mechanical
properties namely coefficient of thermal expansion, and elastic and shear moduli were
studied using thermo-mechanical analyzer and resonant ultrasound spectroscope respectively
in 25-900°C temperature range. A non-linear variation in elastic and shear moduli- indicative
of the structural changes in the studied temperature range was observed for most of the
above mentioned materials. Coefficient of thermal expansion (CTE) was also found to
increase non-linearly with temperature and sensitive to the phase transformations occurring
in the materials. Above a certain temperature (high temperature region- above 600°C), a
significant contribution from chemical expansion of the materials was also observed.
In order to determine thermal stress distribution in the positive electrode, electrolyte,
negative electrode (PEN) assembly, CTE and elastic and shear moduli of the component
materials were incorporated in finite element analysis at temperature of concern. For the
finite element analysis, anode supported configuration of PEN assembly (of 100mm x
100mm) was considered with 1mm thick anode, 10μm electrolyte and 30μm cathode. The
results have indicated that cathode and anode layer adjacent to cathode/electrolyte and
electrolyte/anode interface respectively are subjected to tensile stresses at the operating
temperature of HT-SOFC (900°C) and IT-SOFC (600°C). However, the magnitude of
stresses is much higher in the former case (500MPa tensile stress in cathode layer) when
compared with the stress level in IT-SOFC (178MPa tensile stress in cathode layer). These
high stresses might have been resulted from the higher CTE of cathode when compared with
the adjacent electrolyte. However, it is worth mentioning here that in the present work, we
have not considered any contribution from the residual stresses arising from fabrication and
the stress relaxation from softening of the glass sealant.
30
Masmoudi, Radhouan A. "Modeling and control of geometric and thermal properties in arc welding." Thesis, Massachusetts Institute of Technology, 1993. http://hdl.handle.net/1721.1/12336.
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Xu, Shuangyan. "Evaluating Thermal and Mechanical Properties of Electrically Conductive Adhesives for Electronic Applications." Diss., Virginia Tech, 2002. http://hdl.handle.net/10919/27112.
Full textAbstract:
The objective of this study was to evaluate and gain a better understanding of the short-term impact performance and the long-term durability of electrically conductive adhesives for electronic interconnection applications. Three model conductive adhesives, designated as ECA1, ECA2 and ECA3, supplied by Emerson & Cuming, were investigated, in conjunction with printed circuit board (PCB) substrates with metallizations of Au/Ni/Cu and Cu, manufactured by Triad Circuit Inc.
Effects of environmental aging on the durability of conductive adhesives and their joints were evaluated. All the samples for both mechanical tests and thermal tests were aged at 85%, 100%RH for periods of up to 50 days. Studies of bulk conductive adhesives suggested that both plasticization, which is reversible and further crosslinking and thermal degradation, which are irreversible, might have occurred upon exposure of ECAs to the hot/wet environment. The durability of electrically conductive adhesive joints was then investigated utilizing the double cantilever beam (DCB) test. It was observed that the conductive adhesive joint was significantly weakened following hydrothermal aging, and there was a transition from cohesive failure to interfacial failure as aging continued. A comparative study of the durability of different conductive adhesive and substrate metallization combinations suggested that the resistance of the adhesive joints to moisture attack is related to the adhesive properties, as well as the substrate metallizations. It was noted that the gold/adhesive interface had better resistance to moisture attack than the copper/adhesive interface. A reasonable explanation of this phenomenon was given based upon the concept of surface free energy and interfacial free energy. XPS analysis was performed on the fractured surfaces of DCB samples. For adhesive joints with copper metallization, copper oxide was detected on the failed surfaces upon exposure of the conductive adhesive joints following aging. XPS analysis on the fractured surfaces of adhesive joints with Au metallization suggested that diffusion of Cu to the Au surface might have happened on the Au/Ni/Cu plated PCB substrates during aging.
The impact performance of conductive adhesives was quantitatively determined using a falling wedge test. This unique impact resistance testing method could serve as a useful tool to screen conductive adhesives at the materials level for bonding purpose. Moreover, this test could also provide some useful information for conductive adhesive development. This study revealed that the viscoelastic energy, which is a result of the internal friction created by chain motions within the adhesive material, played an important role in the impact fracture behavior of the conductive adhesives. This study also demonstrated that the loss factor, evaluated at the impact environment conditions, is a good indicator of a conductive adhesive's ability to withstand impact loading.Ph. D.
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DeVincent, Sandra Marie. "Interfacial effects on the thermal and mechanical properties of graphite/copper composites." Case Western Reserve University School of Graduate Studies / OhioLINK, 1994. http://rave.ohiolink.edu/etdc/view?acc_num=case1061300766.
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Larsson, Karl. "Influence of nitrocarburization on the thermomechanical fatigue properties of ductile iron for exhaust components : Analysis and comparisons of TMF-properties." Thesis, Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-72033.
Full textAbstract:
New stricter environmental legislation requires lower emissions and fuel consumption of automotive engines. Therefore the fuel efficiency must be increased but this leads to higher loads in the engine. As for the exhaust system it is affected by higher thermomechanical loads. Until today the turbo manifold has been nitrocarburized in order to increase the wear resistance in slip joints with other exhaust components. The problem is that there is no knowledge of how the nitrocarburizing affects the thermomechanical properties of the material. The purpose of this thesis work is to examine the difference in thermomechanical properties with and without nitrocarburizing on the three different ductile irons High Silicon, SiMo51 and SiMo1000 intended for exhaust components. Thermo-mechanical fatigue (TMF) experiments were performed on test rods to evaluate difference in number of cycles to failure. In each cycle the test-rod was affected by a combination of mechanical loads and thermal loads resembling those found on exhaust components. Light optical microscopy, scanning electron microscopy and x-ray radiography were used to examine microcracks and damage mechanisms of the materials. It was found that the nitrocarburizing did not affect the number of cycles to failure in any large extent. Further, it was also found that SiMo1000 on average has the longest lifetime followed by SiMo51 and High Silicon. Although, the difference is small for many loadings and taking a 95% confidence band into account the curves overlap for many loading cases.
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Trojanowski, Albin S. "Thermomechanical properties of polymers at high rates of strain." Thesis, University of Oxford, 1997. http://ora.ox.ac.uk/objects/uuid:a2c20a83-094d-4293-8c5f-665640c1ce5a.
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-1 were achieved when testing specimens and this rate was obtained using a split Hopkinson pressure bar. A substantial number of preliminary tests were conducted in order to obtain a suitable specimen size which was then used in the temperature measurement process. Quasistatic, intermediate and high strain-rate tests were performed; the last utilised the radiometer for temperature measurement. An Eyring plot was constructed from which fundamental values for activation volumes and enthalpies were obtained. Full descriptions of the testing techniques used have been included and a brief photoelastic analysis has been carried out on a partially deformed specimen which shows molecular alignment.
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Sheng, Nuo 1977. "Multiscale micromechanical modeling of the thermal/mechanical properties of polymer/clay nanocomposites." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/38264.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.Includes bibliographical references (leaves 210-217).
Polymer/clay nanocomposites have been observed to exhibit enhanced thermal/mechanical properties at low weight fractions (We) of clay. Continuum-based composite modeling reveals that the enhanced properties are strongly dependent on particular features of the second-phase "particles"; in particular, the particle volume fraction (f,), the particle aspect ratio (L/t), and the ratio of particle thermal/mechanical properties to those of the matrix. These important aspects of as-processed nanoclay composites require consistent and accurate definition. A multiscale modeling strategy is employed to account for the hierarchical morphology of the nanocomposite: at a lengthscale of thousands of microns, the structure is one of high aspect ratio particles within a matrix; at the lengthscale of microns, the clay particle structure is either (a) exfoliated clay sheets of nanometer level thickness or (b) stacks of parallel clay sheets separated from one another by interlayer galleries of nanometer level height, and the matrix, if semi-crystalline, consists of fine lamella, oriented with respect to the polymer/nanoclay interfaces. Here, quantitative structural parameters extracted from XRD patterns and TEM micrographs (the number of silicate sheets in a clay stack, N, and the silicate sheet layer spacing, d(ool)) are used to determine geometric features of the as-processed clay "particles", including L/t and the ratio of fp to We.
(cont.) These geometric features, together with estimates of silica lamina elastic and thermal expansion properties obtained from molecular dynamics simulations, provide a basis for modeling effective thermal/mechanical properties of the clay particle. In the case of the semi-crystalline matrices (e.g., nylon 6), the transcrystallization behavior induced by the nanoclay is taken into account by modeling a layer of matrix surrounding the particle to be highly textured and therefore mechanically anisotropic. Micromechanical models (numerical as well as analytical) based on the "effective clay particle" were employed to calculate the overall anisotropic elastic constants, anisotropic coefficient of thermal expansion (CTE), and anisotropic yield surface of the amorphous and semi-crystalline polymer-clay nanocomposites and to compute their dependence on the matrix and clay properties as well as internal clay structural parameters. The proposed modeling technique captures the strong modulus enhancements observed in elastomer/clay nanocomposites as compared with the moderate enhancements observed in glassy and semi-crystalline polymer/clay nanocomposites.
(cont.) For the case where the matrix is semi-crystalline, the enhancements of composite modulus and strength are found to rely on different functions of the clay: while the modulus enhancement can be explained by the conventional role of "stiff filler", the strength enhancement of the nanocomposite mainly lies in the improvements of the matrix property achieved through the matrix transcrystallization induced by nanoclay the "nucleation sites". When the nanocomposite experiences a morphological transition from intercalated to completely exfoliated, an abrupt jump in the composite initial yield strength, as opposed to the moderate increase in the overall composite modulus, was predicted. The elastic moduli and anisotropic CTE for MXD6-clay and nylon 6-clay nanocomposites predicted by the micromechanical models are in excellent agreement with experimental data. In summary, continuum-based micromechanical models can provide robust predictions of the overall thermal/mechanical properties of polymer/clay nanocomposites, with the employment of a reliable method to account for the intrinsically hierarchical morphology of the nanoclay, and for the special matrix morphology and properties adjacent to the nanoclay.
by Nuo Sheng.
Ph.D.
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Appiah, Kwadwo Ampofo. "Microstructural and microanalytical characterization of laminated (C-SiC) matrix composites fabricated by forced-flow thermal-gradient chemical vapor infiltration (FCVI)." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/14910.
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Duerr, Joachim Karl Wilhelm. "Finite element analysis of thermal stresses in semiconductor devices." PDXScholar, 1990. https://pdxscholar.library.pdx.edu/open_access_etds/4215.
Full textAbstract:
The failure of integrated circuit due to Silicon fracture is one of the problems associated with the production of a semiconductor device. The thermal stresses, which result in die cracking, are for the most part induced during the cooling process after attaching the die with Gold-Silicon solder. Major factors for stress generation in material systems are commonly large temperature gradients and substantial difference in coefficients of thermal expansion.
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Xie, Weidong. "Thermo-mechanical evaluation of interfacial integrity in multilayered microelectronic packages." Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/17380.
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Sharma, Bed P. "Effect of sonication on thermal, mechanical, and thermomechanical properties of epoxy resin /." Available to subscribers only, 2009. http://proquest.umi.com/pqdweb?did=1966551531&sid=3&Fmt=2&clientId=1509&RQT=309&VName=PQD.
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Razavi, Nouri Mohammed. "The thermal and mechanical properties of polypropolene metallocene polyethylenes and their blends." Thesis, University of Birmingham, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269781.
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Nicholson, E. D. "The mechanical and thermal properties of protective thin films for infrared applications." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319866.
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Eliason, Jeffrey Kristian. "Optical transient grating measurements of micro/nanoscale thermal transport and mechanical properties." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/98819.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 109-119).
The laser-based transient grating technique was used to study phonon mediated thermal transport in bulk and nanostructured semiconductors and surface wave propagation in a monolayer of micron sized spheres. In the transient grating technique two picosecond pulses are crossed to generate a spatially periodic intensity profile. The spatially periodic profile generates a material excitation with a well-defined wave vector. The time dependence of the spatially periodic material response is measured by monitoring the diffracted signal of an incident probe beam. Non-diffusive thermal transport was observed in thin Si membranes as well as bulk GaAs at relatively short (micron) transient grating periods. First-principles calculations of the phonon mean free paths in Si and GaAs were compared with experimental results and showed good agreement. Preliminary measurements on promising thermoelectric materials such as PbTe and Bi2Te3 are presented showing evidence of non-diffusive transport at short length scales. The transient grating technique was used to measure the thermal conductivity of Si membranes with thickness ranging from 15 nm to 1518 nm. Using the Fuchs-Sondheimer suppression function along with first-principles results, the thermal conductivity as a function of membrane thickness was calculated. The calculations showed excellent agreement with experimental measurements. A convex optimization algorithm was employed to reconstruct the phonon mean free path distribution from experimental measurements. This marks the first experimental determination of the mean free path distribution for a bulk material. Thermal conductivity measurements at low temperatures in a 200 nm Si membrane indicate the breakdown of the diffuse boundary scattering approximation. The transient grating technique was used to generate surface acoustic waves and measure their dispersion in a monolayer of 0.5 - 1 [mu]m diameter silica spheres. The measured dispersion curves show "avoided crossing" behavior due to the interaction between an axial contact resonance of the microspheres and the surface acoustic wave at a frequency of -200MHz for the 1 [mu]m spheres and -700 MHz for the 0.5 [m spheres. The experimental measurements were fit with an analytical model in which the contact stiffness was the only fitting parameter. Preliminary results of surface acoustic wave propagation in microsphere waveguides, transmission through a microsphere strip, and evidence of a nonlinear response in a 2D array of microspheres are presented.
by Jeffrey Kristian Eliason.
Ph. D.
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Mariano, Marcos. "Applications of cellulose nanocrystals : thermal, rheological and mechanical properties of new materials." Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAI046/document.
Full textAbstract:
Malgré ces propriétés intéressantes et l'abondance du matériau brut dont on peut les extraire, les applications des CNC pour des produits commerciaux restent limitées en raison des limitations liées à l’utilisation de procédés industriels. En effet, les matériaux produits à base de CNC sont généralement préparés par la technique de coulée/évaporation. Ce procédé permet de bien contrôler les propriétés comme l’humidité, la dispersion des particules et aussi d’assurer la formation d'un réseau tridimensionnel des particules. Cependant, ce procédé n'est pas facilement transposable à l'industrie. Une alternative à la technique de coulée/évaporation serait l'application du procédé d'extrusion et/ou de moulage par injection. Ces n'utilisent pas de solvants et peuvent donc être considérés comme des procédés plus verts que la coulée/évaporation. Il y a cependant des points négatifs. Ils sont essentiellement associés à des problèmes de dispersion, de dégradation thermique et de propriétés mécaniques plus faibles. Dans ce contexte, la thèse développée ici présente quelques études qui cherchent à combler quelque unes des lacunes décrites ci-dessus.Le Chapitre 1 présente une revue de la littérature et des concepts de base utilisés pendant la thèse. Dans le Chapitre 2, les particules de caoutchouc présentes dans la suspension de latex ont été oxydées en surface par addition de KMnO4 en conditions contrôlées. L’objectif était d’induire l’oxydation des doubles liaisons présentes dans la structure du caoutchouc naturel (NR). Les essais de traction cycliques ont montré que pour ces échantillons, les interactions interfaciales entre les nanoparticules et le polymère sont plus fortes. Cependant, quand le taux d’oxydation augmente, l’hydrophilie des chaînes de caoutchouc est observable.Dans le Chapitre 3, des composites à base de polycarbonate (PC) et de CNC ont été obtenus par la technique d’extrusion. Ce procédé implique de hautes températures (200oC) et la dégradation thermique devient alors un problème pendant la préparation des matériaux. Pour limiter cette dégradation, un mélange maître (masterbatch) contenant environ 30% de CNC a été produit et utilisé comme base pour la préparation des films. La dispersion des CNC entre les chaînes de PC permet probablement d’éviter la dégradation en raison de la protection physique des nanoparticules. Malheureusement, la présence des CNC semble réduire la stabilité thermique du polymère et accélérer sa dépolymérisation. Le chapitre 4 est dédié aux systèmes à base de polybutyrate-adipate-téréphtalate (PBAT) et de nanocristaux de cellulose. Le chapitre est divisé en deux parties. La première partie est focalisée sur l’influence de la cristallisation que les nanocristaux peuvent induire sur la matrice polymère après le processus d’extrusion. Trois sources différentes de CNC ont été choisies pour permettre l’obtention de nanoparticules avec différents facteurs de forme L/d. Des nanocomposites ont été préparés par extrusion en utilisant un taux de particules correspondant au seuil de percolation. Cela a créé une sorte de compétition entre la taille de la particule et sa fraction volumique. Dans cette étude, les nanocristaux avec plus grand rapport longueur/diamètre et sont, également, responsables de la cristallisation la plus significative.Dans la deuxième partie, des nanocomposites ont également été préparés par extrusion/injection puis caractérisés en termes d’organisation structurale. Les résultats de SAOS ont montré un changement de viscosité et de la valeur de G’, ainsi que dans la pente de la courbe G’ x ω, suggérant une modification de la structure des particules après conditionnement. Grâce à les tests de rheologie 2D, il a été possible d’observer une modification de la structure des particules qui suggère une plus grande dispersion. Cependant, il est clair que les particules ne sont pas complètement réorganisées sous forme de réseau 3DThe preparation of composites based on cellulose nanocrystals (CNC) is normally performed using techniques such as melt processing or casting/evaporation. In the last one, impressive mechanical properties can be reached due to the creation of a particle 3D network that is based on new hydrogen bonds between the cellulose nanorods. This process of new H-bond formation normally takes time and is dependent of the nanoparticle size and its volume fraction. Besides, the quality of filler dispersion into the polymeric matrix is also an important parameter to provide the highest surface area and provides an ideal structure for the rigid structure. In this work, we tried to propose different preparation methods and characterizations to obtain nanocomposites with a simple preparation either by casting/evaporation or melt processing.First, we improve the compatibility between an hydrophobic matrix and CNC by the chemical modification of the former. This approach tried to be an alternative to standard modification process, normally performed on nanoparticle surface by –OH groups substitution. As a good model for the study of composite mechanical properties, a natural rubber matrix was used with double bonds oxidized by the use of a strong oxidant aiming to introduce new hydroxyl groups on the isoprene chains. These new groups seem to interact with the cellulose surface, creating new supramolecular interactions between particle and matrix. It was observed that the increase in the degree of oxidation can first increase the compatibility between the polymer and the filler, increasing the mechanical properties. Later, over-oxidation starts to cause the plasticization of the system.In sequence, we had use melt processing for produce nanocomposites at high temperatures by using amorphous and semi-crystalline polymers. In a first approach, CNC were coated with the matrix polymer (polycarbonate) by a system of dilution/precipitation in suitable solvents. The coated nanocrystals are extruded with polycarbonate at 230ºC thanks to the coating approach, that allows an increase in the processing temperature of CNCs. Also, this technique improves its dispersion in the matrix due to entanglement of the polymer chains and the individual nanocrystals. The thermal analyzes shows that the CNC presence and coating masterbatch preparation reduces the polycarbonate Activation Energy (Ea) causing an acceleration in its thermal degradation and a molecular weight (Mv) reduction. As consequence, an increase in the crystallinity of the material occurs. Mechanical characterizations (DMA) show that nanocrystals presence and Mv reduction incresed the mechanical properties of the materials. The modulus (E') values, after the Tg, are higher than theoretical values calculated by Halpin−Kardos model for all studied compositions.The last part of this work is focused on investigate the influence of extrusion and thermal history of the material on its mechanical and rheological properties.In a first approach, we investigated the role of CNCs with different sizes on the material’s final properties (i.e. crystallinity and mechanical properties). Different sources were used to obtain CNCs with different percolation volume fractions, aiming to investigate its capacity on crystallization of a semi crystalline thermoplastic matrix. The results showed that crystallinity and mechanical properties are, indeed, strongly affected by the aspect ratio of the nanorod. In fact, longer CNC particles seem to be more capable to create crystalline domains and reinforce the polymer despite the lower total number of particles. In a second step, the rheological properties of the materials were investigated to characterize the effect of particle micro-structure. The composite internal organization seems to be dependent of the system viscosity and filler volume fraction, what can bring strong impact on the mechanical properties of the material
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Sharma, Bed Prasad. "Effect of sonication on thermal, mechanical, and thermomechanical properties of epoxy resin." OpenSIUC, 2009. https://opensiuc.lib.siu.edu/theses/113.
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Epoxy resin is an important engineering material in many industries such as electronics, automotive, aerospace, etc not only because it is an excellent adhesive but also because the materials based on it provide outstanding mechanical, thermal, and electrical properties. Epoxy resin has been proved to be an excellent matrix material for the nanocomposites when including another phase such as inorganic nanofillers. The properties of a nanocomposite material, in general, are a hybrid between the properties of matrix material and the nanofillers. In this sense, the thermal, mechanical, and electrical properties of a nanocomposite may be affected by the corresponding properties of matrix material. When the sonication is used to disperse the nanofillers in the polymer matrix, with the dispersal of the nanofillers, there comes some modification in the matrix as well and it finally affects the properties of nanocomposites. In this regard, we attempted to study the thermal, mechanical, and dynamic properties of EPON 862 epoxy resin where ultrasonic processing was taken as the effect causing variable. Uncured epoxy was subjected to thermal behavior studies before and after ultrasonic treatment and the cured epoxies with amine hardener EPICURE 3223 (diethylenetriamine) after sonications were tested for mechanical and dynamic properties. We monitored the ultrasonic processing effect in fictive temperature, enthalpy, and specific heat capacity using differential scanning calorimetry. Fictive temperature decreased whereas enthalpy and specific heat capacity were found to increase with the increased ultrasonic processing time. Cured epoxy rectangular solid strips were used to study the mechanical and dynamic properties. Flexural strength at 3% strain value measured with Dillon universal testing machine under 3-point bending method was found to degrade with the ultrasonic processing. The storage modulus and damping properties were studied for the two samples sonicated for 60 minutes and 120 minutes. Our study showed that the 60 minutes sonicated sample has higher damping or loss modulus than 120 minutes sonicated sample.
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Tanrikulu, Ahmet Alptug. "Microstructure and Mechanical Properties of Additive Manufacturing Titanium Alloys After Thermal Processing." PDXScholar, 2017. https://pdxscholar.library.pdx.edu/open_access_etds/4088.
Full textAbstract:
Titanium alloys are widely used for aerospace and biomaterial applications since their high specific strength, and high corrosion resistivity. Besides these properties, titanium is an excellent biocompatible material widely used for internal body implants. Because the products have complex geometries in both applications, Additive Manufacturing (AM) methods have been recently applied for production. AM methods can process a direct 3-D shape of the final product, decrease total production time and cost. However, high residual stress of the final product limits the application of AM components, especially the ones that are exposed to cyclic loading. In the present study, the initial microstructures and impact toughness of Ti6Al4V processed by EBM and CMT, and CP:Ti processed by SLM were experimented. In addition to initial microstructure and impact toughness, their response to different heat treatments were examined. Gleeble® 3500 was used for rapid heat treatment process. The change of mechanical properties due to different heat treatments were monitored with impact tests. Phase transformation kinetics of CP:Ti and Ti6Al4V were investigated with a Differential Scanning Calorimeter at slow heating and cooling rates. Microstructure examination was done with a scanning electron microscope. EBSD data was used to analyze the microstructure behavior. It is observed that toughness of the samples that are produced by powder-based AM methods were improved. Overall, residual stress, strain values, and grain orientation are the key elements that affected impact toughness AM produced components.
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Sperling, Evan Andrew. "Processing, mechanical properties, and thermal stability of nickel-aluminide multilayered thin films." The Ohio State University, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=osu1409231969.
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Woodmansee, Michael W. "Thermal cycling and rate-dependent stress relaxation behavior of solders." Thesis, Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/17301.
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Surya, Ramakrishna. "Synthesis and Characterization of Polyimide/Polyacrylonitrile Blend." University of Cincinnati / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1574417741513506.
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Lankford, Maggie E. "Measurement of Thermo-Mechanical Properties of Co-Sputtered SiO2-Ta2O5 Thin Films." University of Dayton / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1627653071556618.
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Bonin, Michael. "An investigation into the properties of starch-based foams." Thesis, Brunel University, 2010. http://bura.brunel.ac.uk/handle/2438/6872.
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This thesis reports research to investigate the mechanical, thermal and acoustic properties of biodegradable foams in block forms based on wheat starch and developed at Brunel University's School of Engineering & Design, in order to exploit the potential environmental benefits of this renewable and biodegradable class of materials. Two emergent novel technologies have been developed based on a combination of the extrusion foaming of starch in conjunction with the natural adhesive characteristics of moistened starch to produce block foams. Regular Packing & Stacking (RPS), and Compression Bonded Loosefill (CBL), are foam fabrication technologies which have both demonstrated the potential to produce bulk foams based on wheat starch with unique structures and properties - a new class of foam materials in the form of macro-composites reinforced by a network of high-density bonding interfaces. This thesis, as part of a Department of Trade & Industry/Technology Strategy Board funded project, reports an investigation into the following areas to address the scientific and technical issues involved in the further development of the materials and their applications. - The basic properties of the raw materials used in the manufacture of CBL and RPS foams are outlined and the fabrication and preparation of these starch-based foams are described. The limitations of these production techniques are discussed with preliminary work and suggestions made for their enhancement. - Research into the mechanical properties of the CBL and RPS foams includes compression, tensile, creep and dynamic impact tests, whilst the mechanical behaviour of the foams subject to high temperature and high humidity conditions is also reported. - Research into the thermal properties of CBL and high density RPS foams includes testing of the material's thermal conductivity. This aspect of the research also involved a case study detailing the use of RPS in a commercial thermal insulation application. - Research into the acoustic properties of CBL and RPS foams includes tests for sound absorption coefficient and sound transmission loss. - Data obtained from these tests are benchmarked against data pertaining to the mechanical, thermal and acoustic properties of conventional polymer foams in order to provide a basis on which to identify the potential cushioning, thermal insulation and acoustic insulation applications of the starch-based materials. The research has demonstrated the following: - Potential cushioning applications include those limited to the range of static loads within the capabilities of the materials, taking into account the resilience of CBL and RPS which is likely to be compromised by successive impacts. - Tensile forces tend to exploit weaknesses in the macrostructure of these materials. By implication the behaviour of the materials under shear forces would be expected to be similarly compromised. - CBL and RPS exhibited dimensional shrinkage, density increase and significantly reduced mechanical properties under conditions of high temperature and humidity. This suggests that neither CBL nor RPS foams would be suitable for applications in regions where tropical conditions may be encountered unless used in conjunction with other protective materials which would not acutely increase the environmental burden of the products. - Low-density RPS and CBL foams exhibit lower thermal conductivities and hence higher thermal insulation properties compared to many commercially available polymer foams of similar densities. As such these foams have the potential to be used in applications in which a measure of thermal insulation is required. A case study based on an existing commercial application in which the temperature of chilled products must be maintained over a 24 hour period reinforced these findings. - The performance of CBL and RPS starch foams would not provide sufficient functionality to be employed in applications in which dedicated acoustic performance is required, although their sound absorption capabilities may facilitate overall marketability for applications in which a degree of acoustic performance is required if used in conjunction with other materials which demonstrate good acoustic performance. It is anticipated that this work will make significant contributions toward advances in the development of these novel technologies, specifically in terms of establishing an understanding of the properties of the starch-based materials and in identifying potential applications. The research results should thus provide a fundamental element in the basis for the industrial development of these renewable and biodegradable materials.