Dissertations / Theses on the topic 'Material and Mechanical Characterization'
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Dixon, Larie Alecia Brandy. "Material characterization of lithium ion batteries for crash safety." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/100106.
Full textAbstract:
Thesis: Nav. E., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015.Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 113-114).
The safety of lithium-ion batteries is extremely important due to their widespread use in consumer products such as laptops and cell phones. Several cases of thermal runaway in lithium ion batteries that resulted in fires have been reported recently. And in the case of vehicle batteries, deformation during a crash event could cause an internal short circuit, leading to thermal runaway, fires, or toxic gas release. While much is understood about lithium-ion batteries, no comprehensive computational models exist to test and optimize these batteries before manufacture. The objective of this research was to characterize the mechanical properties of three types of lithium-ion batteries through cell and interior component mechanical testing. Prismatic, elliptic, and pouch cells were tested using hemispherical punches to obtain load-displacement curves. Elliptic and pouch cells were also compression tested. Uniaxial, biaxial, and compression tests were performed on the interior components of elliptic and pouch cells. The test results were then used by Impact and Crashworthiness Laboratory team members to create, validate, and refine computational models. This research resulted in many conclusions involving the lithium-ion cells, their interior components, and efforts to model the failure of cells. At the cell level, the effect of liquid presence, strain rate, separator type, and test location was studied. The level of experience in sample preparation and testing methods was an important result for interior component material characterization, as was the varied force-displacement results for different cell types. But most importantly, this work demonstrated that the material characterization of lithium-ion battery cells through mechanical testing could be used to create, calibrate, and validate cell numerical simulation models.
by Larie Alecia Brandy Dixon.
Nav. E.
S.M.
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Webster, Matthew R. "Material Characterization of Insect Tracheal Tubes." Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/71708.
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The insect respiratory system serves as a model for both robust microfluidic transport and mate- rial design. In the system, the convective flow of gas is driven through local deformations of the tracheal network, a phenomenon that is dependent on the unique structure and material properties of the tracheal tissue. To understand the underlying mechanics of this method of gas transport, we studied the microstructure and material properties of the primary thoracic tracheal tubes of the American cockroach (Periplaneta americana). We performed quasi-static uniaxial tests on the tissue which revealed a nonlinear stress-strain response even under small deformations. A detailed analysis of the tissue's microstructural arrangement using both light and electron mi- croscopy revealed the primary sources of reinforcement for the tissue as well as heterogeneity on the meso-scale that may contribute to the physiological function of the tracheae during respi- ration. Finally, a custom mechanical testing system was developed with which inflation-extension tests on the tracheae were used to gather data on the biaxial elastic response of the tissue over a wide range of physiologically relevant loading conditions. From information gathered about the material microstructure, a robust constitutive model was chosen to quantify the biaxial response of the tracheae. This model will provide a basis from which to simulate the behavior of tracheal net- works in future computational studies. This study gives the first description of the elastic response of the tracheae which is essential for understanding the mechanics of respiration in insects. Thus it brings us closer to the realization of novel bio-inspired microfluidic systems and materials that utilize mechanical principles from the insect respiratory system.Ph. D.
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Marth, Stefan. "Material Characterization for Modelling of Sheet Metal Deformation and Failure." Licentiate thesis, Luleå tekniska universitet, Material- och solidmekanik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-62477.
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Weight reduction is one possibility to reduce fuel consumption and emission of transportation vehicles. Sheet metals are often used in automotive and aerospace applications and therefore the weight reduction achieved by reducing the sheet metals thickness is an important contribution to weight reduction. Increasing the strength of sheet metal materials gives the opportunity to reduce the total weight while maintaining safety. To prove a maintained safety for parts with a decreased weight Finite Element (FE) simulations are commonly used. This leads to a high demand on the simulation precision of sheet metals, where an accurate prediction of the post-necking behaviour of materials is needed. Improved FE simulations are reducing time and costs during the development processes. One application to improve the strength of sheet metals in the automotive industry is the usage of ultra high strength steels, which has constantly increased in usage during the last decades. The development of the press hardening process, where sheet metal blanks are formed and quenched simultaneously, brings new design opportunities. Using press hardening tools with zones that uses different cooling rates sheet metal parts can be produced with tailored properties, to improve their performance. Simulating materials based on the microstructure demands high precision on the plasticity modelling for high strain values. In this thesis work a method to characterize the elasto plastic post necking behaviour of sheet metal materials, the Stepwise Modelling Method (SMM), is presented. The method uses full field measurements of the deformation field on the surface of tensile specimen. The hardening relation is modelled as a piecewise linear in a step by step procedure. The linear hardening parameter is adapted to reduce the residual between experimental and calculated tensile forces. The SMM is used to characterize the post necking behaviour of a ferritic boron steel and the results are compared with the commonly used inverse modelling method. It is shown that the stepwise modelling method characterizes the true stress, true plastic strain relation in an effective and computational efficient way. Furthermore, the SMM is used to characterize the stress state evolution during tensile testing, which is an important factor for failure and fracture modelling. This method is shown in an aerospace application for the nickel based super alloy Alloy 718. The results shows that the stepwise modelling method is an effective and efficient alternative method to characterize the deformation and failure of sheet metals. Based on the results of this method plasticity and fracture models can be characterized in future work.
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Athale, Madhura Athale. "Elastodynamic Characterization of Material Interfaces Using Spring Models." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1503262542890538.
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Snider, James M. "Zinc pot bearing material wear and corrosion characterization." Morgantown, W. Va. : [West Virginia University Libraries], 2004. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=3716.
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Thesis (Ph. D.)--West Virginia University, 2004.Title from document title page. Document formatted into pages; contains xx, 272 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 207-208).
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Studebaker, Seth. "Material modeling and sensor characterization for optimizing footpad force sensing array." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/112542.
Full textAbstract:
Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017.Cataloged from PDF version of thesis.
Includes bibliographical references (page 54).
with the ultimate goal of assisting the elderly and disabled with fall prevention and mitigation as well as providing athletes with critical data for training. The force sensing footpad, originally developed for use on the MIT Cheetah robot, integrates lightweight pressure sensors and a urethane rubber, Smooth-On's Vytaflex@ 20, to sense force in both the normal and shear directions. In previous work, cylindrical footpads with a single pressure sensor of differing heights and diameters were tested by applying displacements to the material. The experimental force and voltage from the pressure sensor were recorded. The thesis aims to provide a Finite Element Analysis (FEA) model in Abaqus that accurately simulates and models the footpad sensors and is validated by the physical experimental results. While previous work had been done to model and simulate the footpad using FEA, little was known about the properties of the Vytaflex@ material and a Neo-Hookean model based on coefficients for a silicone rubber was used to model the footpad. In order to provide accurate simulations, the thesis seeks to determine the best hyperelastic constitutive model to describe the material. Uniaxial tensile, uniaxial compression, planar tension, and volumetric compression tests were performed to determine the hyperelastic material model of the rubber. The Odgen n=2 material model was determined to be the best fit for the data and was used to describe the material properties in the Abaqus simulations. Abaqus models were created to represent the various cylindrical footpads and simulations were run using Abaqus's dynamic explicit analysis. Stress data from the simulation results was then converted to a voltage using an effective sensitivity and intercept adjustment factor. The effective sensitivity and intercept adjustment factor were adjusted until the simulation results matched that of the experiments. Using these constants, the stresses inside the footpad can now be determined from the voltage readings of the pressure sensor.
by Seth Studebaker.
S.B.
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Meier, Joseph D. (Joseph David). "Material characterization of high-voltage lithium-ion battery models for crashworthiness analysis." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/81586.
Full textAbstract:
Thesis (Nav. E. and S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 59-60).
A three-phased study of the material properties and post-impact behavior of prismatic pouch lithium-ion battery cells was conducted to refine computational finite element models and explore the mechanisms of thermal runaway caused by internal short circuit. In phase one, medium and large sized cells at low state of charge (SOC) were impacted or compressed while measuring punch load, displacement, cell voltage, and surface temperature until an internal short circuit was detected, followed by a rise in surface temperature. Results were used to either refine the constitutive cell properties or validate finite element models. In phase two, an exploratory study into the behavior of lithium-ion prismatic pouch battery cells following surface impacts with hemispherical and conical punches (abuse testing) was conducted for the purpose of observing pouch behavior and adequacy of parameter measurement methods. Cells were impacted by steel punches to loads as high as 500 kN while recording punch load, displacement, and pouch surface temperatures, as well as normal and high-speed video footage. Comparisons of load, surface temperature, and thermal runaway for various states of charge and punch types are presented. In the third and final phase of the study, material characterization of cell components was conducted to further refine computational models and draw conclusions regarding the interactions between impacted cell layers and the physical cause of internal short circuits. Results of uniaxial tension tests for coated and uncoated anode and cathode layers, as well as separator layers are presented, as well as conclusions about the use of digital image correlation (DIC) software in such studies. Much of the data generated was used to further refine and validate prismatic pouch lithium-ion battery cell computational models developed by the MIT Impact and Crashworthiness Laboratory. Physical tests conducted in phase one of this study were compared to model simulations, which showed that the models make close approximations for material displacement, and are good predictors of internal short circuit.
by Joseph D. Meier.
Nav.E.and S.M.
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Souto, Nelson Mineiro. "Computational design of a mechanical test for material characterization by inverse analysis." Doctoral thesis, Universidade de Aveiro, 2015. http://hdl.handle.net/10773/15168.
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Doutoramento em Engenharia MecânicaWith the development of full-field measurements methods, recent material parameters identification strategies call upon the use of heterogeneous tests. The inhomogeneous strain fields developed during these tests lead to a more complete mechanical characterization of the sheet metals, allowing the substantial reduction of the number of tests in the experimental database needed for material parameters identification purposes. In the present work, an innovative design optimization process for the development of heterogeneous tests is presented. The main goal is the design of a mechanical test able to characterize the material behavior of thin metallic sheets under several stress and strain paths and amplitudes. To achieve this aim, the study was carried out with a virtual material, though derived from experimental data. An indicator of the mechanical interest of the test was proposed, and was used in an optimization procedure to design both the boundary conditions and the sample shape. On the one hand, the virtual behavior of a mild steel was characterized using a complex phenomenological model composed by the Yld2004-18p anisotropic yield criterion combined with a mixed isotropic-kinematic hardening law and a macroscopic rupture criterion. An efficient material parameters identification process based on finite element model updating type was implemented and the identified parameters set was validated by performing a deep drawing test leading either to full drawing or rupture of the blank. On the other hand, an indicator which rates the strain field of the experiment by quantifying the mechanical information of the test was formulated. The relevance of the indicator was stressed out by the numerical analysis of already known classical as well as heterogeneous tests and the results obtained were validated by a material parameter sensitivity study. Two different optimization approaches were used for designing the heterogeneous test, namely (i) a one-step procedure designing both specimen shape and loading path by using a tool and (ii) a sequential incremental technique designing the specimen shape and the loading path of the specimen considering local displacements. The results obtained revealed that the optimization approach proposed was very promising for designing a single experiment able to fully characterize the several strain paths and amplitudes encountered in sheet metal forming processes.
Devido ao desenvolvimento de métodos de medição global, recentes estratégias de identificação de parâmetros de material baseiam-se na informação obtida em testes mecânicos heterogéneos. Os campos de deformação desenvolvidos por estes testes permitem uma melhor caracterização mecânica de chapas metálicas, o que possibilita reduzir consideravelmente o número de testes mecânicos necessários num processo de identificação de parâmetros de modelos constitutivos complexos. No presente trabalho, uma metodologia de design recorrendo a optimização para desenvolver testes mecânicos heterógenos é apresentada. O seu principal objectivo consistiu na concepção de um teste mecânico capaz de caracterizar o comportamento mecânico de chapas metálicas para vários estados de tensão e deformação. Para isso, este estudo foi realizado considerando um material virtual obtido a partir de dados experimentais. Além disso, um indicador capaz de caracterizar testes mecânicos foi proposto para ser posteriormente utilizado na metodologia de optimização. Por um lado, o comportamento virtual de um aço macio foi caracterizado através de um modelo fenomenológico complexo composto pelo critério de plasticidade anisotrópico Yld2004-18p, combinado com uma lei de encruamento mista e com um critério macroscópico de ruptura. Para esta caracterização mecânica, um processo eficiente de identificação de parâmetros foi desenvolvido e o conjunto de parâmetros identificado foi validado comparando resultados experimentais e numéricos do processo de embutidura de um copo cilíndrico. Por outro lado, um indicador quantitativo para avaliar a informação do campo de deformação de testes mecânicos foi formulado e a sua performance foi avaliada através da análise numérica tanto de testes mecânicos clássicos como de testes heterogéneos. Relativamente à metodologia de optimização, duas abordagens diferentes foram consideradas para a concepção do teste mecânico heterógeno. A primeira abordagem consistiu num procedimento de etapa única projectando a forma do provete e o carregamento através da utilização de uma ferramenta. A segunda abordagem consistiu numa técnica incremental de varias etapas projectando a forma do provete e o caminho de deformação através da aplicação de carregamento por deslocamentos locais. Os resultados obtidos revelaram que a metodologia de optimização proposta permite a concepção de testes mecânicos capazes de caracterizar toda a gama de estados de deformação e níveis de deformação normalmente observados nos processos de conformação de chapas metálicas.
Grâce au développement des méthodes de mesure de champs, de nouvelles stratégies d’identification de paramètres matériau de lois de comportement mécanique sont proposées, fondées sur l’utilisation d’essais mécaniques hétérogènes. Les champs de déformation hétérogènes développés au cours de ces essais permettent une meilleure caractérisation du comportement mécanique des tôles métalliques et, par conséquent, de réduire considérablement le nombre d’essais nécessaires pour identifier les paramètres matériau de modèles phénoménologiques complexes. Mais comment concevoir ces essais? Dans ce travail, une méthodologie d’optimisation pour le développement d’essais mécaniques hétérogènes est présentée. L’objectif principal est la conception, par analyse inverse et en proposant un indicateur représentatif des états de déformation, d’un essai capable de caractériser le comportement mécanique des tôles métalliques pour plusieurs états de contrainte et déformation. Pour cela, cette étude a été réalisée en considérant un matériau virtuel (acier doux sous forme de tôle mince), obtenu à partir de données expérimentales. En outre, un indicateur qui caractérise les essais mécaniques a été proposé pour être utilisé dans la méthodologie d’optimisation. D’un côté, le comportement mécanique de l’acier doux a été représenté avec un modèle phénoménologique complexe composé du critère anisotrope de plasticité Yld2004-18p, combiné à une loi d’écrouissage mixte et un critère macroscopique de rupture. Pour cette loi de comportement, un procédé d’identification des paramètres du matériau a été développé et le jeu de paramètres identifiés a été validé en comparant des résultats expérimentaux et numériques de l’emboutissage d’un godet cylindrique. D’un autre côté, un indicateur quantitatif pour évaluer l’information du champ de déformation des essais mécaniques a été formulé et sa pertinence a été évaluée à travers l’analyse numérique d’essais classiques et hétérogènes de la littérature. Concernant la méthodologie d’optimisation, deux approches différentes ont été considérées pour la conception de l’essai mécanique hétérogène. La première approche est fondée sur une procédure en une seule étape, où l’optimisation de la forme de l’éprouvette et des conditions aux limites, imposées par un outil, a été effectuée. La seconde approche est fondée sur une technique incrémentale en plusieurs étapes, en optimisant la forme de l’éprouvette et le chemin de déformation, par l’application des déplacements locaux. Les résultats obtenus sont comparés et un essai est retenu pour identifier les paramètres matériau, en utilisant le matériau virtuel comme référence, afin d’illustrer la pertinence de la démarche.
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Hemmasizadeh, Ali. "Characterization of Heterogeneous Material Properties of Aorta Using Nanoindentation." Diss., Temple University Libraries, 2013. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/240046.
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Mechanical EngineeringPh.D.
Arterial mechanical properties have received increasing attention in the past few decades due to their vast effect on predicting cardiovascular diseases and injuries. The heterogeneity of thoracic aortic tissue was characterized in terms of viscoelastic material properties and correlations were obtained between these properties and tissue morphology. Additionally, the effect of material preservation on the material properties was determined. Changes in the mechanical properties of porcine thoracic aorta wall in the radial direction were characterized using a quasi-linear viscoelastic modeling of nanoindentaiton tests. Two layers of equal thickness were mechanically distinguishable in descending aorta based on the radial variations in the instantaneous Young's modulus E and reduced relaxation function G(t). Overall, comparison of E and Ginf of the outer half (70.27±2.47 kPa and 0.35±0.01) versus the inner half (60.32±1.65 kPa and 0.33±0.01) revealed that the outer half was stiffer and showed less relaxation. The results were used to explain local mechanisms of deformation, force transmission, tear propagation and failure in arteries. A multimodal and multidisciplinary approach was adopted to characterize the transmural morphological properties of aorta. The utilized methods included histology and multi-photon microscopy for describing the wall micro-architecture in the circumferential-radial plane, and Fourier-Transform infrared imaging spectroscopy for determining structural protein, and total protein content. The distributions of these quantified properties across the wall thickness of the porcine descending thoracic aorta were characterized and their relationship with the mechanical properties was determined. It was revealed that there is an increasing trend in mechanical stiffness, Elastic lamella Density (ELD), Structural Protein (SPR), Total Protein (TPR), and Elastin and Collagen Circumferential Percentage (ECP and CCP) from inner layers toward the outer ones. Finally two larger regions with equal thickness (inner and outer halves) were determined based on cluster analysis results of ELD which were in agreement with the cluster analysis of instantaneous Young's modulus. Changes to the local viscoelastic properties of fresh porcine thoracic aorta wall due to three common storage temperatures (+4 oC, -20 oC and -80 oC) within 24 hours, 48 hours, 1 week and 3 weeks were characterized. The changes to both elastic and relaxation behaviors were investigated considering the multilayer, heterogeneous nature of the aortic wall. For +4 oC storage samples, the average instantaneous Young's modulus (E) decreased while their permanent average relaxation amplitude (Ginf) increased and after 48 hours these changes became significant (10%, 13% for E, Ginf respectively). Generally, in freezer storage, E increased and Ginf showed no significant change. In prolonged preservation (> 1 week), the results of +20 oC storage showed significant increase in E (20% after 3 weeks) while this increase for -80 oC was not significant, making it a better choice for tissue cold storage applications. Results from this dissertation present a substantial step toward the anatomical characterization of the aortic wall building blocks and establishing a foundation for understanding the role of microstructural components on the functionality of blood vessels. A better understanding of these relationships would provide novel therapeutic targets and strategies for the prevention of human vascular disease.
Temple University--Theses
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Rastgar, Agah Mobin. "Material Characterization of Aortic Tissue for Traumatic Injury and Buckling." Diss., Temple University Libraries, 2015. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/324268.
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Mechanical EngineeringPh.D.
While traumatic aortic injury (TAI) and rupture (TAR) continue to be a major cause of morbidity and mortality in motor vehicle accidents, its underlying mechanisms are still not well understood. Different mechanisms such as increase in intraluminal pressure, relative movement of aorta with respect to mediastinal structures, direct impact to bony structures have been proposed as contributing factors to TAI/TAR. At the tissue level, TAI is assumed to be the result of a complex state of supra-physiological, high rate, and multi-axial loading. A major step to gain insight into the mechanisms of TAI is a characterization of the aortic tissue mechanical and failure properties under loading conditions that resemble traumatic events. While the mechanical behavior of arteries in physiological conditions have been investigated by many researchers, this dissertation was motivated by the scarcity of reported data on supra-physiological and high rate loading conditions of aorta. Material properties of the porcine aortic tissue were characterized and a Fung-type constitutive model was developed based on ex-vivo inflation-extension of aortic segments with intraluminal pressures covering a range from physiological to supra-physiological (70 kPa). The convexity of the material constitutive model was preserved to ensure numerical stability. The increase in ë_è from physiological pressure (13 kPa) to 70 kPa was 13% at the outer wall and 22% at the inner wall while in this pressure range, the longitudinal stretch ratio ë_z increased 20%. A significant nonlinearity in the material behavior was observed as in the same pressure range, the circumferential and longitudinal Cauchy stresses at the inner wall were increased 16 and 18 times respectively. The effect of strain-rate on the mechanical behavior and failure properties of the tissue was characterized using uniaxial extension experiments in circumferential and longitudinal directions at nominal strain rates of 0.3, 3, 30 and 400 s-1. Two distinct states of failure initiation (FI) and ultimate tensile strength (UTS) were identified at both directions. Explicit direct relationships were derived between FI and UTS stresses and strain rate. On the other hand, FI and UTS strains were rate independent and therefore strain was proposed as the main mechanism of failure. On average, engineering strain at FI was 0.85±0.03 for circumferential direction and 0.58±0.02 for longitudinal direction. The engineering strain at UTS was not different between the two directions and reached 0.89±0.03 on average. Tissue pre-failure linear moduli showed an average of 60% increase over the range of strain rates. Using the developed material model, mechanical stability of aorta was studied by varying the loading parameters for two boundary conditions, namely pinned-pinned boundary condition (PPBC) and clamped-clamped boundary condition (CCBC). The critical pressure for CCBC was three times higher than PPBC. It was shown that the relatively free segment of aorta at the isthmus region may become unstable before reaching the peak intraluminal pressures that occur during a trauma. The mechanical instability mechanism was proposed as a contributing factor to TAI, where elevations in tissue stresses and strains due to buckling may increase the risk of injury.
Temple University--Theses
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Dallon, Kathryn Lanae. "Characterization of Mechanical Properties of Battery Electrode Films from Acoustic Resonance Measurements." BYU ScholarsArchive, 2017. https://scholarsarchive.byu.edu/etd/6620.
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Measurements of the mechanical properties of lithium-ion battery electrode films can be used to quantify and improve manufacturing processes and to predict the mechanical and electrochemical performance of the battery. This thesis demonstrates the use of acoustic resonances to distinguish among commercial-grade battery films with different active electrode materials, thicknesses, and densities. Resonances are excited in a clamped circular area of the film using a pulsed infrared laser or speaker and responses are measured using an electret condenser microphone. A numerical model is used to quantify the sensitivity of resonances to changes in mechanical properties. When the numerical model is compared to simple analytical models for thin plates and membranes, the battery films measured here trend more similarly to the membrane model. Resonance measurements are also used to monitor the drying process. Results from a scanning laser Doppler vibrometer verify the modes excited in the films, and a combination of experimental and simulated results is used to estimate the Young's modulus of the battery electrode coating layer.
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Pazos, Valerie. "Characterization of non-linear material parameters of atherosclerosis arteries using numerical and experimental models." Thesis, McGill University, 2010. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=86882.
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Cardiovascular diseases are the leading cause of death worldwide. In most cases, cardiovascular diseases are caused by an underlying pathology: atherosclerosis. Numerical models are very helpful to study the biomechanics of atherosclerosis, assess the risks and more likely sites of rupture, to design and study the effect of interventions. Yet, the reliability of the simulations is directly dependent on the fidelity of the material properties, geometry and boundary conditions to represent the reality. However, data available to precisely model the mechanical behaviour of the plaque and its constituents are relatively limited, particularly for the inclusions.The main objective of this project is to propose a method to determine the non-linear material parameters for an inclusion and for the surrounding tissues of atherosclerotic medium arteries using numerical and experimental models. To evaluate the proposed method, a mock artery with a stenosis and a lipid inclusion was designed and fabricated with polyvinyl alcohol gel for each of the two wall layers, and animal fat (lard) for the inclusion. PVA gel has a non-linear elastic behaviour that can be described with a Money-Rivlin model.
The experimental part of the approach consists in extension-pressurization of the intact vessel. For different states of axial extension, the vessel is pressurized while intravascular ultrasound images are acquired at regular intervals. Then, the images are segmented to extract the contours of the different constituents. The contours from before the pressurization are use to build the geometry of finite element models. Simulations are run for different pressure values. The resulting deformed contours are compared to the contours extracted from the images for the same pressure values, to optimize the material parameters for the inclusion and for the wall layers. The comparison is defined in terms of circumferences and thicknesses.
The estimated material parameters for the gels were applied to predict the responses in uniaxial and biaxial tensions, to compare them to experimental data from tension testing of samples made of the same gels. The estimated parameter for the lard was compared to shear test measurements. The predictions were good (R2 ≥ 0.90) for deformations in the range and slightly over the range of those used for the optimisation process.
Les maladies cardiovasculaires constituent la première cause de mortalité dans le monde. Dans la majorité des cas, elles sont causées par une pathologie sous-jacente, l'athérosclérose. Les modélisations numériques sont d'une grande aide pour étudier la biomécanique de la plaque d'athérosclérose, évaluer les risques et sites de rupture les plus probables, concevoir et étudier l'effet d'interventions. Cependant, les données disponibles pour modéliser avec précision le comportement mécanique de la plaque et ses composants sont relativement limitées, en particulier pour les inclusions.
L'objectif principal de ce projet est de proposer une méthode pour déterminer les paramètres des modèles de matériaux non-linéaires pour l'inclusion et tissus adjacents d'artères athérosclérotiques, à l'aide de modèles expérimentaux et numériques. Afin d'évaluer la méthode proposée, une pseudo-artère imitant une artère coronaire sténosée avec une inclusion lipidique a été conçue et fabriquée avec du gel d'alcool de polyvinyle (PVA) pour chacune des deux couches de la paroi et du saindoux pour l'inclusion. Le gel de PVA a un comportement élastique non-linéaire pouvant être décrit à l'aide d'un modèle de Mooney-Rivlin.
La partie expérimentale de l'approche consiste à soumettre le vaisseau à des tests d'extension-pressurisation. Pour différents états d'extension axiale, le vaisseau est pressurisé tandis que des images par ultrasons intravasculaires sont enregistrées. Ces images sont ensuite segmentées pour extraire les contours des différents constituants. Les contours avant pressurisation sont utilisés pour construire la géométrie de modèles par éléments finis. Des simulations sont exécutées pour différentes valeurs de pression. Les géométries déformées obtenues sont comparées aux contours extraits des images à ces même valeurs de pression afin d'optimiser les paramètres des modèles de matériaux pour l'inclusion et les deux couches de la paroi. Cette comparaison est définie en termes de circonférences et d'épaisseurs.
Les paramètres estimés pour les gels sont appliqués pour prédire les réponses en tensions uniaxiale et biaxiale, et comparer aux données expérimentales de tests tension réalisés sur des échantillons faits des mêmes gels. Le paramètre estimé pour le lard est comparé à des mesures obtenues aves des tests de cisaillement. Les prédictions étaient bonnes (R2 ≥ 0.90) pour des déformations de l'ordre de grandeur et légèrement supérieures à celles utilisées dans le processus d'optimisation.
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Kennedy, Sean P. "Material Characterization of Nitinol Wires for the Design of Actuation Systems." DigitalCommons@CalPoly, 2013. https://digitalcommons.calpoly.edu/theses/1076.
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A series of tests were performed on nickel-titanium alloy wire, also known as nitinol, to determine the plausibility of designing an actuator using this wire as the method of actuation. These tests have been designed to fully characterize how the wire behaves under steady state and transient conditions allowing for a specific wire selection to be made given known actuator specifications which will result in an efficient design. The wire transient data can be used to design a controller which reduces the actuation time. The research done for the overall project covers a wide scope including wire hysteresis, nitinol transition temperature, variable wire resistance, wire actuation as a function of current and pull force, cable fabrication, and wire actuation control to optimize performance. Using these test results, a prototype actuator has been designed using nitinol wire. It has been determined that an actuator can be efficiently designed using this material.
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Moro, Marjan. "Nano-Characterization of Ceramic-Metallic Interpenetrating Phase Composite Material using Electron Crystallography." Youngstown State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1340223324.
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Chang, Ellen E. "Damping Identification of Viscoelastic Coating Material through Finite Element Modal Analysis." University of Cincinnati / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1439295466.
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Stein, Itai Y. "Synthesis and characterization of next-generation multifunctional material architectures : aligned carbon nanotube carbon matrix nanocomposites." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/81728.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013.Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (p. 129-141).
Materials comprising carbon nanotube (CNT) aligned nanowire (NW) polymer nanocomposites (A-PNCs) have emerged as promising architectures for next-generation multifunctional applications. Enhanced operating regimes, such as operating temperatures, motivate the study of CNT aligned NW ceramic matrix nanocomposites (A-CMNCs). Here we report the synthesis of CNT A-CMNCs through the pyrolysis of CNT A-PNC precursors, creating carbon matrix CNT A-CMNCs. The CNT A-CMNC processing parameters were evaluated using an apparent density measurement, polymer re-infusion modeling, and CNT quality analysis, which elucidate the limitations of the processing parameters currently used to fabricate CNT A-CMNCs. Theoretical tools developed to help quantify and analyze the morphology of the CNTs in the A-CMNCs, and NWs in general, show that morphological parameters, such as NW outer diameter and inter-wire spacing, that are usually overlooked may have significant effects on the physical properties of NW architectures. Mechanical characterization of the CNT A-CMNCs illustrates that the presence of aligned CNTs can lead to an enhancement of > 60% in microhardness, meaning that the fabrication of high strength, high temperature, lightweight next-generation material architectures may be possible using the presented method. Finally, factors that influence the physical properties of CNT A-CMNCs, such as CNT waviness and the porosity of the carbon matrix, are identified, and since their effects cannot be modeled using existing theory, future paths of study that could enable their quantification are recommended.
by Itai Y. Stein.
S.M.
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Mason, Amber J. "Material characterization and axial loading response of pouch lithium ion battery cells for crash safety." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/112040.
Full textAbstract:
Thesis: Nav.E., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017.Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 75-76).
Recent research conducted at MIT's Impact and Crashworthiness Laboratory (ICL) has focused on material characterization of lithium ion battery cell components for use in the development of an accurate and practical computational model intended to predict mechanical deformation and related short circuit behavior of Li-ion battery cells and stacks in real world impact scenarios. In an effort to continue to refine and validate this modeling tool, characterization testing was conducted on battery cell pouch material using uniaxial stress and biaxial punch tests. At the full cell level, hemispherical punch indentation validation testing and internal electric short circuit testing was conducted on large, high energy pouch cells. Further investigations at the full cell level examined the buckling response of small pouch cells as a result of in-plane axial compression under varying degrees of confinement. To this end, a custom testing device was designed and constructed to provide controllable cell confinement for axial loading experimentation purposes. All experimentation results will feed into a computational model of the cell extended for use in comprehensive mechanical deformation simulation modeling.
by Amber J. Mason.
Nav.E.
S.M.
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Palm, Gregory O. "Large strain material characterization and modeling of poly(Methyl Methacrylate)(PMMA) near the glass transition." The Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=osu1413458325.
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Hudson, Shaymus William. "Mechanical characterization of jammable granular systems." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/75850.
Full textAbstract:
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2012.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 (p. 36-37).
The mode by which a granular material can transition between fluid-like and solid-like states has been often referred to as jamming. The use of this property (via vacuum pressure) for engineering applications has only recently been explored. Several possible applications are presented. However, thorough characterization of mechanical properties and material selection for jammed systems has not been reported. Glass beads of differing size distributions, silica blasting media, sand, and ground coffee were tested under different vacuum pressures in a procedure similar to an unconsolidated-undrained triaxial compression test for soils. Coffee was found to have the highest strength to weight ratio. Literature predictions of the trend between applied pressure and effective Young' modulus was also investigated.
by Shaymus William Hudson.
S.B.
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O'Brien, Daniel P. "Characterization and Modeling of the In Vivo Mechanical Response of Human Skin Using Handheld Devices." University of Cincinnati / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1337715574.
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Turowski, Daniel J. "Assembly and characterization of mesoscale DNA material systems based on periodic DNA origami arrays." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1374169645.
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Iyengar, Ananth Shalvapulle. "Synthesis and characterization of micro/nano material for thermoelectric applications." Case Western Reserve University School of Graduate Studies / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=case1276182370.
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Miller, Kyle M. (Kyle Mark). "Mechanical characterization of lithium-ion battery micro components for development of homogenized and multilayer material models." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/92133.
Full textAbstract:
Thesis: Nav. E., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014.Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014.
Cataloged from PDF version of thesis.
Includes bibliographical references (page 60).
The overall battery research of the Impact and Crashworthiness Laboratory (ICL) at MIT has been focused on understanding the battery's mechanical properties so that individual battery cells and battery packs can be characterized during crash events. The objective of this research is to better understand the battery component (electrode and separator) properties under different loading conditions. In this work, over 200 tests were conducted on battery components. These tests include uniaxial stress, biaxial punch, multilayer, single layer, short-circuit testing, wet vs dry specimen testing, strain rate testing, and more. Additionally, a scanning electron microscope was used to view the battery components at a micro level for the purpose of better understanding the aforementioned test results. During these tests, it was observed that many of the electrodes in the Li-ion batteries are damaged during the battery manufacturing process. Also, the two methods of manufacturing battery separator were analyzed and their resulting mechanical properties were characterized. These results will be used to further refine and validate a high-level, robust, and accurate computational tool to predict strength, energy absorption, and the onset of electric short circuit of batteries under real-world crash loading situations. The cell deformation models will then be applied to the battery stack and beyond, thereby enabling rationalization of greater optimization of the battery pack/vehicle combination with respect to tolerance of battery crush intrusion behavior. Besides improving crash performance, the finite element models contribute substantially to the reduction of the cost of prototyping and shorten the development cycle of new electric vehicles.
by Kyle M. Miller.
Nav. E.
S.M.
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Sinko, Robert Arnold. "Characterization, Modeling, and Applications of Novel Magneto-Rheological Elastomers." Miami University Honors Theses / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=muhonors1335236738.
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Hussain, Hyder. "Torsion fatigue system for mechanical characterization of materials." Ohio : Ohio University, 2000. http://www.ohiolink.edu/etd/view.cgi?ohiou1172002877.
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Hakoon, Sagy. "Material characterization of Li-ion battery segments subjected to lateral compression and an in-plane tension loads." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/108925.
Full textAbstract:
Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017.Cataloged from PDF version of thesis.
Includes bibliographical references (page 40).
In the last two decades, Lithium-ion (Li-ion) batteries have become an inherent part of day-to-day life thanks to their widespread use in many consumer products and electric vehicles. While these batteries possess great advantages, they also carry an inherent safety liability: In case of a crash event, short-circuit failure of the battery may develop, leading to thermal runaway, fires and even explosions. Hence, a comprehensive study is required, aimed to modulate these batteries and optimize their testing standard. The objective of this research was to characterize the effect of lateral compression on the in-plane tensile failure load of Li-ion battery segments. A new experimental system was developed, which allows fine control of the compression load, and decouples the out-of-plain compression load and the in-plain tension load. Then, measurements were conducted with single-layer, 4-layers and 11-layers specimens, producing characterizing graphs of the tensile load versus displacement. For all types of specimens, results show an observable decrease in the failure load for increasing pre-compression load, as expected. Furthermore, measurements confirmed that the relation between the tensile load and the displacement does not change for different compression loads. For the multi-layer specimens (4 layers), the failure sequence was studied. It was found that the sequence may alter for different pre-compression loads. Nevertheless, on all cases, the cathode failed first, and the anode failed second. Throughout all experiments, failures were located on the edge of the compression area of the specimen. Several methods were used to encourage emergence of failure at the center, but with no success. A hypothesis to explain the development of this mode of failure is suggested at the end of this work.
by Sagy Hakoon.
S.M.
27
Sofia, Wännman. "Influence of Nitrocarburization on Thermo-Mechanical Fatigue Properties : Material Characterization of Ductile Cast Iron for Exhaust Components." Thesis, Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-69160.
Full textAbstract:
The large number of vehicles operating on the roads cause high emissions and consequently a negative effect on the environment. When developing and optimizing internal combustion engines, certain requirements must be considered, which are environmental regulations, reduced fuel consumption and increased specific power. In order to meet these demands, an increase of the engine combustion pressure will occur usually accompanied with a temperature increase. During start-up and shut-down of an engine, it is subjected to cyclic thermo-mechanical fatigue (TMF) loads. The turbo manifold and exhaust manifolds connected to the engine is also subjected to these thermo-mechanical fatigue loads and thereby exposed to alternating tensile and compression loads. As these TMF loads will increase in the near future due to the development and optimization of internal combustion engines, it is important to understand the limitations of the material for these loads. In collaboration with Scania CV AB in Södertälje, this thesis covers the investigation of influence of nitrocarburizing (NC) on TMF properties of three ductile irons (DCI) labelled HiSi, SiMo51 and SiMo1000 intended to be used for components in the exhaust system. Nitrocarburizing is a thermo-chemical process where nitrogen and carbon diffuses from the process medium into the surface zone of a ferrous metal. The purpose of the NC is to increase the wear properties in contact areas between different parts. The oxidation with and without nitrocarburizing are studied both after isothermal and stress free oxidation tests at 780 °C and after TMF loads with combined cyclic variation of mechanical and thermal loads. In addition, the properties such as hardness, defects, porosity, microstructure, composition of both the materials and of the oxide layer have been investigated. For SiMo1000+NC cracks formed during nitrocarburizing were positioned parallel to the surface edge in the diffusion zone and consequently an increased diffusion of nitrogen into the material, i.e. deeper diffusion depth. SiMo1000+NC showed highest hardness, highest compressive residual stresses and thickest oxide layer. SiMo1000 showed highest resistance against oxidation due to the protective aluminum oxide layer. Oxide crack initiations after thermo-mechanical tests with a protective silicon oxide layer around the cracks for HiSi and SiMo51 and a protective aluminum oxide layer around the cracks for SiMo1000. In materials with nitrocarburizing, these protective layers of either silicon oxide or aluminum oxide were more distributed into the material. In SiMo1000+NC, crack initiations were not oxidized.
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Molina, Pombo Juan Cruz. "Mechanical characterization of fabrics for inflatable structures." Morgantown, W. Va. : [West Virginia University Libraries], 2008. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=5844.
Full textAbstract:
Thesis (M.S.)--West Virginia University, 2008.Title from document title page. Document formatted into pages; contains x, 107, 15 p. : ill. Includes abstract. Includes bibliographical references (p. 106-107).
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Chiang, Juei-Chun. "Design and characterization of nanowire array as thermal interface material for electronics packaging." [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-3188.
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Miller, Kyle M. "Mechanical Characterization of Lithium-Ion Battery Micro Components for Development of Homogenized and Multilayer Material Models." Thesis, Monterey, California. Naval Postgraduate School, 2014. http://hdl.handle.net/10945/43074.
Full textAbstract:
CIVINSThe overall battery research of the Impact and Crashworthiness Laboratory (ICL) at MIT has been focused on understanding the battery’s mechanical properties so that individual battery cells and battery packs can be characterized during crash events. The objective of this research is to better understand the battery component (electrode and separator) properties under different loading conditions. In this work, over 200 tests were conducted on battery components. These tests include uniaxial stress, biaxial punch, multilayer, single layer, short-circuit testing, wet vs dry specimen testing, strain rate testing, and more. Additionally, a scanning electron microscope was used to view the battery components at a micro level for the purpose of better understanding the aforementioned test results. During these tests, it was observed that many of the electrodes in the Li-ion batteries are damaged during the battery manufacturing process. Also, the two methods of manufacturing battery separator were analyzed and their resulting mechanical properties were characterized. These results will be used to further refine and validate a high-level, robust, and accurate computational tool to predict strength, energy absorption, and the onset of electric short circuit of batteries under real-world crash loading situations. The cell deformation models will then be applied to the battery stack and beyond, thereby enabling rationalization of greater optimization of the battery pack/vehicle combination with respect to tolerance of battery crush intrusion behavior. Besides improving crash performance, the finite element models contribute substantially to the reduction of the cost of prototyping and shorten the development cycle of new electric vehicles.
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Youssef, Amanda. "Root-cause analysis and characterization of oxygen-related defects in silicon PV material : an approach from macro to nanoscale." Thesis, Massachusetts Institute of Technology, 2018. https://hdl.handle.net/1721.1/122510.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018Cataloged from PDF version of thesis.
Includes bibliographical references (pages 141-155).
With energy demand forecasted to grow significantly, efforts towards mitigating global warming effects by reducing greenhouse gas emissions are becoming stricter as more power generation plants are deployed to meet the global demand. Deployment of renewable energy technologies as a low-carbon alternative to fossil fuel is an attractive solution. Photovoltaics (PV) present several advantages over other energy sources because PV is modular, and has proven to be a scalable and reliable technology. A capital expenditure reduction of 70% has been found to be necessary to meet the climate targets of 7-10 TW of PV by 2030. This can be achieved through different channels: improving conversion efficiency and device performance of silicon modules, increasing solar cell manufacturing yield, reducing silicon feedstock material use, etc. This research focuses on n-type monocrystalline silicon and aims to increase conversion efficiency up to 20% relative and increase manufacturing yield up to 50%, as levers to reduce the capital expenditure. The increase in conversion efficiency and manufacturing yield is achieved by defect engineering and mitigation of a lifetime-limiting bulk defect in n-type monocrystalline silicon, characterized by low-lifetime concentric rings. Temperature- and injection-dependent photoluminescence imaging is applied to investigate the defect's root-cause by studying its evolution under several high temperature process conditions and is found to be caused by oxide-related precipitates. Synchrotron-based mic ...
by Amanda Youssef.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Mechanical Engineering
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Ryglowski, Brian K. "Characterization of Carbon Nanotube-Enhanced water as a phase change material for thermal energy storage systems." Thesis, Monterey, California : Naval Postgraduate School, 2009. http://edocs.nps.edu/npspubs/scholarly/theses/2009/Dec/09Dec%5FRyglowski.pdf.
Full textAbstract:
Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, December 2009.Thesis Advisor(s): Kwon, Young ; Pollak, Randall. "December 2009." Description based on title screen as viewed on February 1, 2010. Author(s) subject terms: Carbon Nanotube, Thermal Energy Storage Systems, Characterization of Nanofluids, Static Phase Change Materials, Heat Transfer Nanofluid Systems. Includes bibliographical references (p. 73-77). Also available in print.
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Chandrasekaran, Gurucharan. "Material Characterization and Modeling of Strain Induced Crystallization in PET above the Glass Transition Temperature." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1218053145.
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Edin, Emil. "Characterization of Heat Treated LMwD Ti-6Al-4V to Study the Effect of Cooling Rate on Microstructure and Mechanical Properties." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-75979.
Full textAbstract:
In this work, the influence of different cooling rates (5, 20, 50 and 100 °C/s) on the microstructure and mechanical properties of Laser Metal Wire Deposited (LMwD) Ti-6Al-4V was investigated, this was done using a thermal-mechanical physical simulation system (Gleeble 3800, DSI). Two different soak times above β transus (held at 1100 °C), 5 and 40 s, were used and after cooling to 150 °C, the samples were tensile tested. The samples were characterized with optical microscopy (OM) and scanning electron microscopy (SEM) and hardness testing. The results were then compared, both with each other and with two reference samples, that were only heated to 150 °C and then tensile tested. It was found that for the lowest cooling rate, 5 °C/s, the microstructure had transformed from a basketweave α microstructure to a colony α microstructure in the center of the specimen waist where heating was most efficient. Ultimate tensile strength (UTS) was found to be in the range of 858 – 977 MPa, with the highest average being recorded for the reference samples, similar results were noted for the strain, with a range of ⁓5 – 14 %, where the highest recorded average was for the reference samples. However, the extensometer used was not optimized for this kind of test, therefore percent reduction of area (RA) measurements were performed. The RA measurements produced a significantly different result than that obtained from the testing, a large scatter in the ductility was found, possibly due to thermal instability that occurred during testing. Overall, the microstructure appears to be relatively stable over the cooling range of 20 - 100 °C/s, no major differences were observed, the microstructure consisted of a homogeneous basketweave α microstructure, with little to no change in the measured average α lath thickness.
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Popelar, Carl Frank. "Characterization of mechanical properties for polyethylene gas pipe materials." Connect to this title online, 1989. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1094830993.
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Piratla, Sarvani. "Fully-Coupled Characterization of Thermo-Electro-Magneto-Mechanical Materials." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1243875108.
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Foster, Daniel. "Mechanical and Thermal Characterization of Ultrasonic Additive Manufacturing." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1398997070.
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Dev, Bodhayan. "Characterization of Ceramic/Glass Composite Seals for Solid Oxide Fuel Cells." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1400847202.
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Altman, Katrina J. "Microscale Machining and Mechanical Characterization of Bone Tissue." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1250522820.
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Walters, Thomas E. "Development Of A Smart Material Electrohydrostatic Actuator Considering Rectification Valve Dynamics And In Situ Valve Characterization." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1211996027.
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Headings, Leon Mark. "Modeling, characterization, and design of smart material driven stick-slip actuation mechanisms." Connect to resource, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1141700440.
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Li, Yuan. "Synthesis and mechanical characterization of transversely isotropic nanoporous platinum." Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42927.
Full textAbstract:
Nanoporous (NP) metal foams combine desirable characteristics of metals with unique nanoarchitectural features to yield weight normalized properties far superior than either dense metals or bulk metal foams. Due to their high surface to volume ratios these structures show great promise as components of fuel cells, as sensors and have been suggested for use in biological applications, for example as antimicrobial scaffolds or as platforms on which to explore biological material behavior. While most NP metal foams are isotropic, structures with anisotropic features spanning different length scales can further extend applications. This work examines the parameters controlling the synthesis of transversely isotropic NP Platinum foam by dealloying an amorphous Pt-Si alloy. The structure that is examined in this work is hierarchical with Voronoi polyhedra that form on the free surface and under each polyhedral hyper-structure, nanocrystalline NP Pt foam forms with radial struts of length ~60 nm and grain size of 5 nm. The size of the polyhedra can be tailored by changing the dealloying potential. In turn, the mechanical properties of these structures as assessed by nanoindentation can range from 1 to 3GPa depending on the geometric arrangement of the struts. Finally, the initiation location of these structures and the relationship between electrochemical parameters and dealloying front evolution is examined.
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Gopalan, Sriram. "Quasi-static and dynamic mechanical characterization of reinforced polyurethane foam /." free to MU campus, to others for purchase, 2003. http://wwwlib.umi.com/cr/mo/fullcit?p1418024.
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Putta, Sriram. "Elastodynamic Numerical Characterization of Adhesive Interfaces Using Spring and Cohesive Zone Models." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu156338398610629.
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Sánchez, Camargo César Moisés. "Mechanical multi-scale characterization of metallic materials by nanoindentation test." Thesis, Toulouse, ISAE, 2019. http://www.theses.fr/2019ESAE0010/document.
Full textAbstract:
Avec le développement des matériaux fonctionnels (multi-matériaux, multicouches,…), la caractérisation du comportement mécanique par des moyens macroscopiques conventionnels est devenue de plus en plus difficile. Ces méthodes conventionnelles sont donc substituées progressivement par des moyens de caractérisation multi-échelles. Parmi ces moyens, la nanoindentation, qui peut résoudre certains défis de la micro-caractérisation tels que la présence de phases indissociables, les systèmes multicouches, les revêtements ultra-minces, etc. Cet outil est devenu une technique de haute précision capable de solliciter des volumes de matière très faibles et fournir des informations riches pour la caractérisation des matériaux. Cependant, cet outil est utilisé majoritairement pour identifier les propriétés élastiques et qualitativement certains paramètres tels que la dureté, la ductilité et les contraintes internes.Ce travail de thèse s’intéresse à la caractérisation du comportement élastoplastique par nanoindentation à deux échelles : l’échelle macroscopique et l’échelle du cristal.Le premier défi de ce travail est expérimental. Il s’agit de générer des surfaces avec des propriétés représentatives de la microstructure étudiée. Ce défi est d’autant plus relevé que le matériau utilisé comme modèle est l’acier 316L très ductile et dont la surface est sensible au moindre changement. Un protocole expérimentale a été mis en place, à l’issu de ce travail, et les erreurs et dispersions de la réponse en nanoindentation introduites par les différentes étapes de génération de surface ont été quantifiés.Une base de données étendue a été mise en place, par la suite. Différentes géométries d’indent ont été appliquées à plusieurs profondeurs. Cette base de données va alimenter des stratégies d’identification inverse basée sur un couplage entre des algorithmes d’optimisation et une modélisation éléments finis de l’essai. Deux types d’algorithme ont été appliqués : Levenberg-Marquardt et l’algorithme génétique. Ce dernier est très consommateur en temps de calcul. Différents modèles EF axisymétrique et 3D ont été utilisés. Ces modèles ont été soigneusement optimisés par rapport au temps de calcul.Plusieurs stratégies d’identification ont été employées en se basant sur différentes données expérimentales issues de l’essai de nanoindentation telles que la courbe de charge-décharge, la forme de l’empreinte résiduelle et l’association de plusieurs géométries d’indent. Plusieurs modèles d’écrouissage isotrope ont été identifiés. À l’échelle macroscopique, les modèles d’écrouissage isotrope classiques ont été déterminés. À l’échelle du grain, la loi cristalline de Méric et Cailletaud a été identifiée. Les résultats obtenus ont été confrontés, à l’échelle macroscopique, à des identifications réalisées sur le même matériau à partir des essais de traction et de compression et ont montré que l’association de multiples géométries d’indentation permet de reproduire le comportement volumique du 316L avec une précision acceptable. Pour le comportement du cristal, des essais de compression de micropilliers ont été utilisé pour se procurer des données de référence à cette échelle. La comparaison montre beaucoup de dispersion dans les deux cas. En effet, certains phénomènes liés à la densité de dislocation très variables d’un grain à l’autre sont responsables de cette dispersion. Cette densité de dislocation n’est pas prise en compte, en tant que variable, dans le modèle cristallin utilisé. L’utilisation d’un modèle plus physique intégrant la densité de dislocation et son évolution permet d’améliorer ces résultats. Enfin, une nouvelle méthode d’identification a été proposée. Cette méthode est basée sur l’estimation et l’introduction de la géométrie réelle de l’indent dans le modèle EF utilisé pour l’identification. La méthode a été validée dans le cas de la pointe Berkovich et elle montre des résultats très prometteursWith the development of functional materials (multi-materials, multilayers, ...), the mechanical behavior characterization by conventional macroscopic methods has become progressively difficult. These conventional methods are therefore gradually substituted by multiscale characterization processes. Among these methods, the nanoindentation, this can solve certain challenges of micro-characterization such as the presence of indissociable phases, multilayer systems, ultra-thin coatings, etc. This tool has become a high-precision technique capable of testing very small volumes of matter and providing rich information for material characterization. However, this tool is used mainly to identify the elastic properties and, qualitatively, some parameters such as hardness, ductility and internal stresses.This thesis work focuses on the characterization of elastoplastic behavior by nanoindentation at two scales: the macroscopic scale and the crystal scale.The first challenge of this work is experimental. It involves generating surfaces with properties representative of the studied microstructure. This challenge is important because the material used as a model is 316L steel which is very ductile and whose surface is sensitive to small perturbations. An experimental protocol was implemented at the end of this work, and the errors and dispersions of the nanoindentation response introduced by the different surface generation steps were quantified. Then, a wide database was implemented with different indenter geometries and several depths. This database will feed inverse identification strategies based on a coupling between optimization algorithms and finite element modeling of this test. Two types of algorithm have been applied: Levenberg-Marquardt and genetic algorithms. The latter is very consumer in computing time. Different axisymmetric and 3D FE models have been used. These models have been carefully optimized with respect to computation time.Several identification strategies were employed based on various experimental databases from the nanoindentation test such as the loading-unloading curve, the residual imprint shape and the association of several indent geometries. Some models of isotropic hardening have been identified. On the macroscopic scale, classical isotropic hardening models have been determined. At the grain scale, the crystal plasticity constitutive model of Méric and Cailletaud has been identified. The results obtained were compared on the macroscopic scale with identifications carried out on the same material from the tensile and compression tests. The comparison showed that the combination of multiple indentation geometries makes it possible to reproduce the volume behavior of the 316L with acceptable accuracy. For crystal behavior, micropillar compression tests were used to obtain reference data at this scale. The comparison shows a lot of dispersion in both cases. Indeed, some phenomena related to the density of dislocation very variable from one grain to another are responsible of this dispersion. This dislocation density is not taken into account, as a variable, in the used crystal constitutive model. The use of a more physical law integrating the dislocation density and its evolution makes it possible to improve these results. Finally, a new identification method has been proposed. This method is based on estimating and introducing the real indent geometry in the FE model used for identification. The method has been validated in the case of Berkovich tip and shows very promising results
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Monelli, Bernardo Disma. "Mechanical Characterization of Metallic Materials by Instrumented Spherical Indentation Testing." Doctoral thesis, Università degli studi di Trento, 2010. https://hdl.handle.net/11572/368675.
Full textAbstract:
Instrumented indentation testing is now considered one of the most attractive tools for characterizing engineering materials. A large number of materials properties can be investigated. The present dissertation was aimed at developing a new methodology for inferring the material behaviour of metallic materials from their indentation response.
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Chen, Kuo-Shen 1966. "Materials characterization and structural design of ceramic micro turbomachinery." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/9396.
Full text
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Kraemer, Daniel Ph D. Massachusetts Institute of Technology. "Solar thermoelectric power conversion : materials characterization to device demonstration." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/103490.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2016.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 268-289).
Meeting the ever growing global energy demand with mostly fossil fuel based energy technologies is not sustainable, pollutes the environment and is the main cause of climate change threatening our planet as we know it. Solar energy technologies are a promising, sustainable and clean alternative due to the vast abundance of sunlight. Thus far, photovoltaic solar cells and concentrated solar power are considered to be the most promising approaches. Solar cells directly convert sunlight into electricity by photon induced electron-hole pair generation. Concentrated solar power captures the sunlight in form of heat which is then converted to electricity by means of a traditional mechanical power block. In this thesis, we explore solar thermoelectric generators (STEGs) as an alternative way to convert sunlight to electricity. Similar to concentrated solar power STEGs capture the sunlight in form of heat. However, the captured heat is directly converted to electricity by means of a thermoelectric generator. This solid-state direct heat-to-electricity conversion significantly simplifies the system, reduces cost and maintenance and enables transient operation and system scalability without affecting the performance. Therefore, STEGs have the potential to be deployed as small scale solar power converters in remote areas and on rooftops and as large scale concentrated solar power plants. While the concept of solar thermoelectric power conversion has been proposed over a century ago, most successful experimental efforts reported in, the literature have been limited to below 1 % for STEGs without optical concentration and to approximately 3 - 5 % with optical concentration. Theoretical STEG performances as modeled and discussed in this thesis predict significantly higher efficiencies. A detailed STEG model is introduced to theoretically investigate various parasitic losses and how to minimize their effect to obtain highest and most realistic performance predictions. Additionally, a methodology to optimize a photovoltaic-thermoelectric hybrid system based on spectral splitting is introduced. The optimization and performance prediction of a STEG is only accurate if the relevant material properties are known with high accuracy. However, typical spectroscopy techniques to determine the optical properties, namely the solar absorptance and infrared emittance, of a solar absorber have shortcomings which can lead to significant errors. Similarly, typical commercial equipment to measure the properties of thermoelectric materials including the Seebeck coefficient, the electrical resistivity and the thermal conductivity are prone to large errors. Therefore, we introduce in this thesis novel experimental techniques to measure all relevant properties with improved accuracies in particular the techniques to measure the total hemispherical emittance of a surface and a material's thermal conductivity. A record-low total hemispherical emittance of 0.13 at 500 °C is demonstrated for an Yttria-stabilized-Zirconia-based cermet solar absorber with solar absorptance of 0.91 and thermal stability up to 600 °C. Furthermore, a method was developed to directly measure the efficiency of a thermoelectric leg. Using this method a record-high thermoelectric efficiency of 8.5 % is demonstrated at a relatively small temperature difference of 225 °C for a novel MgAgSb-based compound with hot-pressed silver contact pads. By increasing the temperature difference to a material's compatible 275 °C a thermoelectric efficiency of 10 % is achievable which, thus far, has only been achieve at almost twice the temperature difference. The third main contribution of this thesis is the experimental demonstration of solar thermoelectric power conversion. A record-high STEG efficiency of 4.6 % is demonstrated at AM1.5G (1 kW/m 2) conditions which is 7 times higher than previously reported best values. The performance improvement is achieved by using a STEG with nano-structured bulk thermoelectric materials, a spectrally-selective solar absorber and taking advantage of large thermal concentrations under a vacuum. Despite the vacuum environment and the use of a low-temperature spectrally-selective solar absorber the optimal hot-junction operating temperature is limited to approximately 200 °C due to increasing thermal radiation heat loss. In order to substantially increase the operating temperature difference and STEG efficiency, larger incident solar power densities are required. Furthermore, the STEG requires segmented thermoelectric legs and a high-temperature stable solar absorber. The optimized STEGs are fabricated and tested at moderate and high optical solar concentration. Efficiencies of close to 8 % at 38 suns and close to 10 % at 211 suns, measured based on the solar flux at the absorber, are demonstrated for a STEG with a spectrally-selective solar absorber. The maximum demonstrated solar-to-electricity CSTEG efficiency is 7.5 %. Furthermore, the performance of a STEG at moderate optical concentration with a high-temperature stable black paint solar absorber and a directionally-selective solar receiver cavity is demonstrated to be comparable to a STEG with a spectrally-selective surface at similar insolation.
by Daniel Kraemer.
Ph. D.
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Ewoldt, Randy H. (Randy Harold). "Nonlinear viscoelastic materials : bioinspired applications and new characterization measures." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/49556.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Vita.
Includes bibliographical references (p. 297-313).
Viscoelastic materials, such as biomaterials and non-Newtonian fluids, typically experience mechanical loading which evokes a nonlinear rheological response. Rheologically complex materials can provide novel functionality in biological and engineered systems. However, it is found that standard characterization techniques are insufficient to appropriately describe nonlinear viscoelasticity. The goal of this thesis is to transcend the limitations of current characterization methods as well as demonstrate applications of nonlinear viscoelastic materials, including reversible adhesion and snail-like wall climbing. PART ONE of this thesis introduces a complete language and framework (or ontology) for characterizing nonlinear viscoelasticity using large amplitude oscillatory shear (LAOS) deformation. The LAOS protocol spans the 2D parameter space of deformation amplitude and frequency, known as a Pipkin space. Physically meaningful material measures are proposed, corresponding to clearly defined language such as strain-stiffening/softening and shear-thickening/thinning. The new ontology is general enough to be applied to any viscoelastic material, mapping behaviors from purely elastic to purely viscous, and any complex response in-between. The framework has been packaged into a distributable data analysis program (MITlaos) to widen its use in both academic and industrial settings. PART TWO examines the nonlinear rheological response of various soft materials and constitutive models.
(cont.) The new framework is illustrated by examining prototypical nonlinear constitutive models (Giesekus, pseudoplastic Carreau, and elastoplastic Bingham). Various soft materials are tested experimentally, including pedal mucus gel from terrestrial gastropods, a wormlike micelle solution, ultrasoft hagfish slime, and an oilfield drilling fluid. PART THREE describes the use of nonlinear rheological behavior to enable unique functionality, specifically for bioinspired snail-like wall climbing and tunable adhesion using magnetorheological fluids. Yield stress fluids are examined here to enable the bioinspired adhesive locomotion of a self-contained mechanical device (Robosnail, developed by Brian Chan, Ph.D. '09). Field-responsive magnetorheological fluids are analyzed in the context of providing fast-switching reversible adhesion for use with adhesive locomotion devices and shape-changing soft robots. In conclusion, interest in soft materials is increasing across many disciplines. The contributions presented here provide the means to a better understanding of biological and engineered systems which involve complex viscoelastic materials.
by Randy H. Ewoldt.
Ph.D.
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Yao, Jing. "Characterization of Mechanical Properties of Thin-Film Li-Ion BatteryElectrodes from Laser Excitation and Measurements ofZero-Group Velocity Resonances." BYU ScholarsArchive, 2019. https://scholarsarchive.byu.edu/etd/7128.
Full textAbstract:
The mechanical properties of thin-film Li-ion battery electrodes are controlled by the micro structure of the constituent materials. In this work, a non-contact and non-destructive measurement of the mechanical properties of electrode films is performed by measurement of zero group velocity (ZGV) resonances. The ZGV Lamb wave modes of a solid bi-layer consisting of a thin metallic layer and a thin compliant coating layer are shown to be dependent on the Young's moduli, thicknesses, densities and Poisson ratios of the layers. Theoretical models are used to quantify the sensitivity of the ZGV resonances to changes in mechanical properties. Experimental ZGV resonances are excited using a pulsed infrared laser and detected using a laser interferometer. Commercial-grade battery films with different coating materials, densities and thicknesses are measured. Young's moduli of the battery electrode layers are estimated using the combination of a theoretical model and experimental results. The effect of the calendering process on the battery materials is also investigated. Results suggest that the Young's modulus of the electrode coating increases drastically after the battery films are calendered. This technique can be used to quantitatively study the mechanical properties of Li-ion battery electrodes to improve overall battery performance.