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1
Robeck, Eric Dean. « The effects of fault-induced stress anisotropy on fracturing, folding and sill emplacement : insights from the Bowie coal mines, southern Piceance basin, western Colorado / ». Diss., CLICK HERE for online access, 2005. http://contentdm.lib.byu.edu/ETD/image/etd760.pdf.
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2
Charsley, Andrew Darrin. « Interpretation of sleeve fracturing for stress measurement ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0010/MQ61252.pdf.
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3
Kim, Kwangmin. « Rock Fracturing & ; Mine to Mill Optimization ». Diss., The University of Arizona, 2012. http://hdl.handle.net/10150/242456.
Texte intégralRésumé :
The research presented in this dissertation consists of four topics. The first of these topics is an experimental study of rock fracturing due to rapid thermal cooling, and the other three topics are related to mine-to-optimization. This includes the development and testing of a site-specific model for blast fragmentation, the development of a technique for utilizing digital image processing and ground-based LIDAR for rock mass characterization, and an experimental study of the effects of ore blending on mineral recovery. All four topics are related through the subject of rock fracturing and rock fragmentation. The results from this research are important and can be used to improve engineering design associated with rock excavation and rock fragmentation. First of all, a successful set of laboratory experiments and 3D numerical modeling was conducted, looking at the effects of rapid thermal cooling on rock mechanical properties. The results gave the unexpected finding that depending on the rock type and the thermal conditions, rapid cooling can result in either overall crack growth or crack closing. Secondly, a site-specific model for predicting blast fragmentation was developed and tested at an open-pit copper mine in Arizona. The results provide a practical technique for developing a calibrated blasting model using digital images and digital image processing software to estimate in-situ block size, and a calibrated Schmidt hammer to estimate intact tensile strength. Thirdly, a new technique was developed to conduct cell mapping in open-pit mines using the new technologies of digital image processing and ground-based LIDAR. The results show that the use of these new technologies provide an increased accuracy and the ability for more sophisticated slope stability analyses with no increase in field time only a moderate increase in data processing time. Finally, a successful set of laboratory experiments was conducted looking at the effects of ore blending and grinding times on mineral recovery from a set of six ore from a copper mine in Arizona. The results gave the unexpected finding that for a fixed grinding time, the mineral recovery of the blended ores exceeded the average of the individual recoveries of the same ores unblended.
4
Tang, Yin-tong. « Rock stress determination in Hong Kong Island by using hydraulic fracturing method / ». View the Table of Contents & ; Abstract, 2005. http://sunzi.lib.hku.hk/hkuto/record/B36357625.
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5
Tang, Yin-tong, et 鄧燕棠. « Rock stress determination in Hong Kong Island by using hydraulic fracturing method ». Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2005. http://hub.hku.hk/bib/B45014322.
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6
Anyanwu, Ezechukwu John. « Low Alloy Steel Susceptibility to Stress Corrosion Cracking in Hydraulic Fracturing Environment ». University of Dayton / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1398948610.
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7
nn, Arthur Glenn Arthur. « Microseismicity in the Ekofisk field : faulting and fracturing in a compacting chalk reservoir ». Thesis, University of Bristol, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.551325.
Texte intégralRésumé :
Passive microseismic monitoring provides a non-invasive method of monitoring deformation and changes in the stress distribution within a rock mass. Recently the petroleum industry has applied and focussed such studies on the monitoring of hydraulic fracturing stimulation: the fracturing of a reservoir by the injection of a high pressure fluid into reservoir causing the rock to fracture, increasing the permeability. However, the development of passive seismic monitoring of a fully operational oil field has been slow largely due to economic constraints limiting the geophone array to be deployed within a single vertical borehole. The challenge is thus to refine the seismic methods applied to datasets from the vertical arrays and to explore the extent to which further investment in more sophisticated seismic arrays would advance the understanding of the reservoir architecture and evolution. The Ekofisk reservoir in the North Sea provides an excellent opportunity to address these issues and is the focus of this study. Discovered in 1969 the Ekofisk field is located within the Central Graben of the Norwegian North Sea and is operated by Conoco-Phillips. It was one of the world's first economically viable chalk reser- voirs and comprises two main oil bearing intervals: the Ekofisk and Tor Formation chalks, separated by a relatively impermeable siliceous chalk. Since the onset of production in 1971, the reservoir has expe- rienced appreciable subsidence. A water injection program was initiated but has done little to mitigate the problem. In April 1997, one of the first hydrocarbon passive micro seismic monitoring studies was undertaken over an 18 day period at Ekofisk in an attempt to understand the mechanism of deformation. Data were acquired using a six station geophone array deployed in a vertical borehole. Fundamental to the study of seismicity at any scale is the accurate determination of the event source. Events for borehole microseismics are usually located using a ID velocity model, P- and S-wave arrival times and the polarisation azimuth of the P-wave particle motion. However, in the case of all sensors being deployed within a vertical or near-vertical bore hole such analysis leads to an inherent 1800 ambiguity in source location. In this study, this ambiguity is removed by using the back-projecion of the dip of the particle motion from multiple stations until they converge on one side of the well or the other as a priori information to constrain the initial source location. The procedure is developed and tested using a dataset acquired from another field during hydraulic fracture stimulation, where event locations are known. Applying this procedure to the Ekofisk dataset 627 events are successfully located with coherent features clustering around production/waterflooding wells and fractures. Most are located less than 250 m away from the monitoring well and at a depth of ",3 km in the Ekofisk chalk formation. Little seismicity is observed from the underlying Tor Formation chalk, which is separated from the Ekofisk Formation by an impermeable layer of siliceous chalk. There is no evidence of seismicity in the overburden. Repeating earthquakes (multiplets) are identified and relatively re-located in order to enhance the resolution of active features and gain further insight into the mechanism of deformation. Qualitative analysis of the waveforms of the multiplets shows a number of potential mechanisms such as production/waterflooding induced activity, fault re-activation and stress triggering. Having established precise hypocentres for the Ekofisk microseismicity the final goal of this study is to gain information along the source-receiver raypath using a shear wave splitting study of anisotropy. An automated shear wave splitting approach is applied to the Ekofisk dataset yielding 1125 reliable measurements. A number of near-vertical fracture sets with fracture strike orientations of NE-SW and W-SE agrees with previous core based studies of Ekofisk. In summary, this thesis shows that a single borehole deployment of geophones can be used to gather detailed information about the spatial and temporal variation in seismicity in a hydrocarbon setting. The seismic data can then be used via study of seismic anisotropy to place fundamental new constraints on the state of stress, mineral alignment, layering of sedimentary structures or the presence of aligned fracture sets all of which have profound implications for reservoir management.
8
Stafford, Catherine Elizabeth. « An experimental study of the compaction and creep behaviour of oolitic sands ». Thesis, University College London (University of London), 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312997.
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9
Du, Jing. « Geophysical inversion of far-field deformation for hydraulic fracture and reservoir information / ». Digital version accessible at:, 2000. http://wwwlib.umi.com/cr/utexas/main.
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10
Dölle, Michael. « Field effect transistor based CMOS stress sensors / ». Tönning ; Lübeck Marburg : Der Andere Verlag, 2006. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=016086105&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.
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11
Woolard, Deonna Faye. « Thermoelastic and photoelastic full-field stress measurement ». W&M ScholarWorks, 1999. https://scholarworks.wm.edu/etd/1539623969.
Texte intégralRésumé :
Photoelasticity is an optical technique that measures the difference of the principal stresses plus the principal stress direction. A complementary technique is thermoelasticity which measures the sum of the principal stresses. Combining these two full-field, non-contact nondestructive evaluation techniques allows the individual stress components to be measured. One of the main difficulties in merging these two measurement systems is in identifying an appropriate surface coating. Thermoelasticity demands a highly emissive surface, while photoelasticity requires a thick, stress-birefringent, transparent coating with a retro-reflective backing. Two coatings have been identified that can be used for combined thermoelastic and photoelastic stress measurements: PMMA and polycarbonate.;An anisotropic electromagnetic boundary value model was developed to understand more fully the mechanisms through which photoelastic stress patterns are produced. This model produced intensity contour maps which matched the fringe patterns observed in the laboratory, and allowed the effect of measurement errors on the calculated stress tensor to be quantified. One significant source of error was the retro-reflective backing, which depolarized the light and degraded the resulting photoelastic fringes. A quantitative analysis of the degraded fringes, to be used as a rating scheme for reflective backing materials, showed that the isoclinic lines shift position as a result of the backing roughness and oblique incidence. This is a concern when calculating the stress components through the combination of photoelasticity and thermoelasticity because the data maps are integrated at the pixel level. Small shifts in the photoelastic fringes result in incorrect information being assigned to some pixels and hence lead to uncertainties in the stress tensor components. Progress in the understanding of the depolarization at the reflective backing allows the specification of new materials that will minimize this effect, as well as the development of robust computer algorithms to correct for any remaining depolarization.
12
Valley, Benoît Christian. « The relation between natural fracturing and stress heterogeneities in deep-seated crystalline rocks at Soultz-sous-Forêts (France) / ». Zürich : ETH Reprozentrale Hönggerberg, HIL C45, Zürich, 2007. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=17385.
Texte intégral
13
Gao, Sui. « In-plane stress analysis using tensor field photoelasticity ». Thesis, University of British Columbia, 2011. http://hdl.handle.net/2429/37059.
Texte intégralRésumé :
Few experimental methods exist for evaluating all in-plane stress components in solid materials; because of the tensor nature of these quantities. Full field measurement of all three stress components is desirable, since plastic deformation or failure can result from any combination of the three. A new photoelastic stress measurement method is presented for evaluating all three in-plane stress components within a two-dimensional photoelastic material. The measurement method is based on the observation that the complex transmission factors that describe the optical phase changes due to stress-induced birefringence have a second order tensor character, similar to that of other tensor quantities such as stress and strain. The same transformation equations and Mohr’s circle construction can be applied to the rotation of optical axis. A Michelson type interferometer and phase shifting are used to quantify the phases of the complex transmission factors. Mohr’s circle calculation is applied to obtain the principal transmission factors and principal axis orientation. The principal stresses are then obtained from the principal transmission factors through the stresss optical relationship. The effectiveness of this technique is demonstrated by comparing the experimental and analytical results for a hollow circular ring under diametric compression.
14
Cristiano, Elena <1988>. « Stress Field and Seismicity at Campi Flegrei Caldera ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amsdottorato.unibo.it/7555/1/cristiano_elena_tesi2.pdf.
Texte intégralRésumé :
Aim of this work is the study of the stress field in the Campi Flegrei caldera during the bradyseismic crisis of 1982-1984.
n the first part of the work has been analysed old cretaceous and digital seismic datasets relative to 70th years, and the bradyseismic crisis of 1982-1984 where has been recorded the earthquakes linked to uplifts that interested Campi flegrei caldera during 1969-72 and 1982-84.
The seismicity dataset has been used to made some analysis as location and focal mechanisms generation. The focal mechanisms are than analysed using two software to determine the principal state of stress that was predominant in that period.
Then, starting from ground deformation data, relative to 1100 optical levelling measure done during the bradyseismic crisis, has been use the inversion method to modelling the source of the deformation. Has been used many model as the Mogi model, the penny shaped-crack, and the rectangular crack of Okada.
Consequently, a joint inversion was applicate on ground deformation data and seismicity together to better understand the dynamic of the stress in the area.In the last part of the work, has been determined the excess of pore pressure in the Flegrean area, using focal mechanisms to study the influence of fluid pore pressure on change in the Coulomb stress of the area.
Has been used the Coulomb-Navier criterion and Terakawa method (2010) to estimate the excess of pore pressure.
Finally, in order to evaluate the reliability of the calculated pore pressures, was done thermo-fluid dynamic simulation and analysed the hydrothermal system of Campi Flegrei caldera. So, has been performed a series of simulation thermo-fluid dynamic injecting a flow in the system varying temperature, pressure and injection rate to model the Campi Flegrei caldera during the unrest.
15
Cristiano, Elena <1988>. « Stress Field and Seismicity at Campi Flegrei Caldera ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amsdottorato.unibo.it/7555/.
Texte intégralRésumé :
Aim of this work is the study of the stress field in the Campi Flegrei caldera during the bradyseismic crisis of 1982-1984.
n the first part of the work has been analysed old cretaceous and digital seismic datasets relative to 70th years, and the bradyseismic crisis of 1982-1984 where has been recorded the earthquakes linked to uplifts that interested Campi flegrei caldera during 1969-72 and 1982-84.
The seismicity dataset has been used to made some analysis as location and focal mechanisms generation. The focal mechanisms are than analysed using two software to determine the principal state of stress that was predominant in that period.
Then, starting from ground deformation data, relative to 1100 optical levelling measure done during the bradyseismic crisis, has been use the inversion method to modelling the source of the deformation. Has been used many model as the Mogi model, the penny shaped-crack, and the rectangular crack of Okada.
Consequently, a joint inversion was applicate on ground deformation data and seismicity together to better understand the dynamic of the stress in the area.In the last part of the work, has been determined the excess of pore pressure in the Flegrean area, using focal mechanisms to study the influence of fluid pore pressure on change in the Coulomb stress of the area.
Has been used the Coulomb-Navier criterion and Terakawa method (2010) to estimate the excess of pore pressure.
Finally, in order to evaluate the reliability of the calculated pore pressures, was done thermo-fluid dynamic simulation and analysed the hydrothermal system of Campi Flegrei caldera. So, has been performed a series of simulation thermo-fluid dynamic injecting a flow in the system varying temperature, pressure and injection rate to model the Campi Flegrei caldera during the unrest.
16
Holland, Austin Adams. « Imaging Time Dependent Crustal Deformation Using GPS Geodesy And Induced Seismicity, Stress And Optimal Fault Orientations In The North American Mid-Continent ». Diss., The University of Arizona, 2014. http://hdl.handle.net/10150/332903.
Texte intégralRésumé :
Transient deformation has been observed in a number of different types of tectonic environments. These transient deformation signals are often observed using continuous GPS (CGPS) position time-series observations. Examining transient deformation using CGPS time-series is problematic due to the, often, low signal-to-noise ratios and variability in duration of transient motions observed. A technique to estimate a continuous velocity function from noisy CGPS coordinate time-series of is examined. The resolution of this technique is dependent on the signal-to-noise ratio and the duration or frequency content of the transient signal being modeled. Short period signals require greater signal-to-noise ratios for effective resolution of the actual transient signal. The technique presented here is similar to a low-pass filter but with a number of advantages when working with CGPS data. Data gaps do not adversely impact the technique but limit resolution near the gap epochs, if there is some a priori knowledge of the noise contained within the time-series this information can be included in the model, and model parameter uncertainties provide information on the uncertainty of instantaneous velocity through time. A large transient has been observed in the North-American stable continental interior as a significant increase in the number and moment release of earthquakes through time. This increase in the number of earthquakes has been suggested to be largely related changes in oil and gas production activities within the region as triggered or induced seismicity, primarily from fluid injection. One of the first observed cases of triggered earthquakes from hydraulic fracturing where the earthquakes were large enough to be felt by local residents is documented. The multiple strong temporal and spatial correlations between these earthquakes indicate that hydraulic fracturing in a nearby well likely triggered the earthquake sequence. The largest magnitude earthquake in this sequence was a magnitude 2.9 with 16 earthquakes greater than magnitude 2. The earthquakes in this sequence occurred within 2.5 km of the hydraulic fracturing operation and focal depths are similar to the depths of hydraulic fracturing treatment depths. In addition to the documentation of a transient earthquake signal associated with hydraulic fracturing, the observed focal mechanisms throughout Oklahoma are documented. These focal mechanisms were used to examine the maximum horizontal stress orientations and active fault orientations associated with the increased rates of seismicity observed in the region. Generally, active-fault orientations and the stresses are consistent through broad portions of Oklahoma with one exception, the ongoing Jones earthquake sequence in central Oklahoma that started in 2009. In the Jones earthquake sequence a bi-modal distribution of focal mechanisms are observed. One orientation of active faults observed in the Jones earthquake sequence would not be expected to be active in the observed regional stress field. This unfavorably oriented set of faults appear to be pre-existing structures and activity on these structures may suggest that pore-pressure increases in the sub-surface due to fluid injection in the area make it possible for faults that are not optimally oriented within the regional stress-field to reactivate.
17
Blake, Kelly. « Crustal Stress Heterogeneity in the Vicinity of a Geothermal Field : Coso Geothermal Field, CA ». Master's thesis, Temple University Libraries, 2011. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/152710.
Texte intégralRésumé :
GeologyM.S.
Borehole induced structures seen in image logs from the Coso Geothermal Field, CA record variation in the azimuth of principal stress. Image logs of these structures from five boreholes were analyzed to quantify the stress heterogeneity for three geologically distinct locations: two boreholes within the Coso Geothermal Field (one in an actively produced volume), two on the margin of the Coso Geothermal Field and outside the production area, and a control borehole several tens of kilometers south of the Coso Geothermal Field. Average directions of Shmin and its standard deviation are similar along the eastern portion of the geothermal field at ~107 ± 28°; this is distinct from the western portion which has an azimuth of 081 ± 18° and also distinct from outside the geothermal field where the average azimuth is 092 ± 47°. These relationships suggest a correlation of stress orientation and heterogeneity with slip on the Coso Wash fault, suggesting that ~20 years of production has not affected the Shmin.orientation. The slope of power spectrum quantifies the length-scale dependence of stress rotations for the volume of the brittle crust penetrated by each borehole. Spectral analysis was applied to the depth variation of stress direction and it demonstrates that: (1) the data set contains distinct wavelengths of stress rotation, (2) that the relative power of these wavelengths in the total scaling of stress directions demonstrates a fractal distribution and (3) in a manner consistent with earthquakes causing the stress rotations. While the vertically averaged Shmin orientation for the three eastern boreholes varied by as little as 1°, the spectral slopes varied by 0.4 log (deg2 *m)(m) from the inside to the margin unproduced areas of the Coso Geothermal Field. The two boreholes inside the field had spectral slopes within one standard deviation, even though Shmin orientations were not parallel. These results suggest that at the kilometer length scale, the source of stress heterogeneity is dominated by proximity to recent fault slip, whereas the centimeter to meter stress heterogeneity is dominated by earthquake activity.
Temple University--Theses
18
Hirsch, Jameson K., K. Bryant Smalley, Emily M. Selby-Nelson, Jane M. Hamel-Lambert, Michael R. Rosmann, Tammy A. Barnes, Daniel Abrahamson et al. « Psychosocial Impact of Fracking : a Review of the Literature on the Mental Health Consequences of Hydraulic Fracturing ». Digital Commons @ East Tennessee State University, 2018. https://dc.etsu.edu/etsu-works/2749.
Texte intégralRésumé :
The process of natural gas extraction known as hydraulic fracturing, or fracking, is a controversial energy acquisition technique often viewed with disdain by the public, due to its potential for environmental harm. However, the mental health and psychological well-being of fracking communities, including potential benefits and detriments, are often overlooked. We reviewed the literature on the association between fracking and psychological functioning, finding that although persons living in fracking communities may experience some minimal, initial benefits such as land lease income or infrastructure development, they may also experience worry, anxiety, and depression about lifestyle, health, safety, and financial security, as well as exposure to neurotoxins and changes to the physical landscape. Indeed, entire communities can experience collective trauma as a result of the “boom/bust” cycle that often occurs when industries impinge on community life. Impacted communities are often already vulnerable, including poor, rural, or indigenous persons, who may continue to experience the deleterious effects of fracking for generations. An influx of workers to fracking communities often stokes fears about outsiders and crime; yet, it must be recognized that this population of mobile workers is also vulnerable, often ostracized, and without social support. Practitioners, researchers, and policy makers alike should continue to investigate the potential psychological ramifications of fracking, so that effective and targeted intervention strategies can be developed, disseminated, and implemented to improve mental health in fracking communities.
19
Cotta, Igor Frederico Stoianov. « Splitting method in multisite damage solids : mixed mode fracturing and fatigue problems ». Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/18/18134/tde-08032016-103918/.
Texte intégralRésumé :
The design of complex structures demands the prediction of possible fracture-dominant failure processes, due to the existence of unavoidable preexistent flaws and other defects, as well as sharps and cracks. On one hand, the complexity of the structure and the presence of many defects to be accounted for in the modeling can become the computational effort impracticable. On the other hand, it is important to seek the development of a computational framework based on some numerical method to study these problems. A way to overcome the difficulties mentioned, therefore making feasible the analysis of complex structures with many cracks, flaws and other defects, consists of combining a representative mechanical modeling with an efficient numerical method. This is precisely the fundamental aim of this work. Firstly, the Splitting Method is used aiming to build a representative modeling. Secondly, the Generalized Finite Element Method (GFEM) is chosen as an efficient numerical method, in which enrichment strategies of the approximated solution using stress functions in particular can be explored. The GFEM framework also allows avoiding the excessive refinement of the mesh, which increases the computational effort in conventional finite element analysis. In the Splitting Method, a kind of decomposition method, the original problem is subdivided in local and global problems which are then combined by imposing null traction at the crack surfaces. In this work, the Splitting Method was completely programmed in Python language and its use extended to analyze crack propagation including fatigue crack growth. The generated code presents in addition to several features related to Fracture Mechanics concepts, as the computation of the stress intensity factor (mode I and II) trough J Integral. Some examples are presented to depict the propagation of the cracks in multisite damage structures. It is shown that for this kind of problems the enrichment strategy provided by GFEM is essential. Moreover, the final example demonstrates that the computational tool allows for investigation of different possible crack scenarios with a low cost analysis. One concludes about the representativeness and efficiency of the methodology hereby proposed.O projeto de estruturas complexas demanda a previsão de possíveis processos de ruptura governados por fraturamento, devido à existência de inevitáveis defeitos pré-existentes, como entalhes e fissuras. Por um lado, a complexidade da estrutura e a presença de muitos defeitos a serem considerados no modelo podem tornar a análise inviável devido ao esforço computacional necessário. Por outro lado, é importante procurar desenvolver uma estrutura computacional baseada em métodos numéricos para estudar estes problemas. Um modo de superar as dificuldades mencionadas, portanto tornando possível a análise de estruturas complexas com muitas fissuras e outros defeitos, consiste em combinar um modelo mecânico que seja representativo com um método numérico eficiente. Este é precisamente o objetivo fundamental deste trabalho. Primeiramente, o Método da Partição é utilizado para a construção de um modelo representativo. Em segundo lugar, o Método dos Elementos Finitos Generalizados (GFEM) é empregado por ser um método numérico eficiente, no qual as estratégias de enriquecimento da solução aproximada usando funções de tensão, em particular, podem ser exploradas. A estrutura do GFEM também permite evitar o excessivo refinamento da malha, que aumenta o esforço computacional em análises convencionais nas quais se utiliza o método dos elementos finitos. No Método da Partição, um tipo de método de decomposição, o problema original é subdividido em problemas locais e globais que são então combinados impondo-se a nulidade do vetor de tensões na superfície da fissura. Neste trabalho, o Método da Partição foi completamente programado em linguagem Python® e sua utilização estendida para analisar a propagação de fissuras, incluindo-se a associação do crescimento com a resposta em fadiga. Além disso, o código gerado apresenta diversas características relacionadas aos conceitos da Mecânica da Fratura, como o cálculo do fator de intensidade de tensão (modos I e II) mediante a Integral J. Alguns exemplos são apresentados para ilustrar a propagação de fissuras em estruturas multi-fraturadas. Mostra-se que para este tipo de problemas a estratégia de enriquecimento fornecida pelo GFEM é essencial. Além disso, o exemplo final comprova que a ferramenta computacional permite a investigação de diferentes possíveis cenários de fissuras com uma análise de baixo custo. Conclui-se sobre a representatividade e eficiência da metodologia proposta.
20
Bas, Gokcen. « Electric Field Analysis In Stress Controlled High Voltage Cables ». Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12605778/index.pdf.
Texte intégralRésumé :
The terminations and the joints are the basic accessories of the power cables. Power cables require electrical stress control when terminated.
Since there are different types of terminations, the analysis should be done to choose the proper method for electric field control problem at the terminations.
Throughout this study two different types of termination methods are investigated by using the finite element analysis program (ANSYS): Stress Controlled Termination Model with Deflector and Stress Control Tube (SCT). The results are compared with those obtained for a cable without stress control model termination.
The numerical calculations are also compared with the measurements obtained by an experimental model: the electrolytic tank model.
21
Luo, Chenyi [Verfasser], et Wolfgang [Akademischer Betreuer] Ehlers. « A phase-field model embedded in the theory of porous media with application to hydraulic fracturing / Chenyi Luo ; Betreuer : Wolfgang Ehlers ». Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2019. http://d-nb.info/1184884099/34.
Texte intégral
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Noii, Nima Verfasser], Lorenzis Laura [Akademischer Betreuer] [De et Peter [Akademischer Betreuer] Wriggers. « Variational-based Global-Local approach for a phase-field formulation of a fracturing material / Nima Noii ; Laura De Lorenzis, Peter Wriggers ». Braunschweig : Technische Universität Braunschweig, 2021. http://d-nb.info/1237412129/34.
Texte intégral
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Riggenbach, Kane Ryan. « Finite Geometry Correction Factors for the Stress Field and Stress Intensities at Transverse Fillet Welds ». Case Western Reserve University School of Graduate Studies / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=case1339121761.
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MYGDALSKYY, VOLODYMYR. « Analysis of stress field of box-like shells with cracks ». 京都大学 (Kyoto University), 2002. http://hdl.handle.net/2433/149381.
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Hussey, I. W. « The influence of notch stress field on fatigue crack growth ». Thesis, University of Portsmouth, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372739.
Texte intégral
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Romero, Juan (Juan Andrés). « Effects of geometry on compliant, stress field force sensor characteristics ». Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/119906.
Texte intégralRésumé :
Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 91-92).
This thesis details the development and characterization of multiple geometries for compliant, stress field (SF) force sensors. The goal of exploring these different sensor designs is to begin identification of the geometric properties of SF force sensors that are most optimal for certain loading conditions. This work prioritizes robotic locomotion as the qualifying loading condition, with some considerations towards human locomotion. The stress field force sensors are comprised of a protected array of piezoelectric pressure sensor elements, embedded in an elastomer body. The geometric properties considered are orientation of the sensor elements, and shape and size of the elastomer body. In previous work, cylindrical stress field force sensors were developed and characterized for use in a force sensing smart-shoe. A material model for the elastomer used was also found. Depending on the geometry chosen, voltage values reported by the piezoelectric sensor elements are able to be resolved into forces along three axes, torques about the non-normal axes, and ground contact angle. This computation is done using linear and nonlinear methods, notably linear regression to determine coefficients for force and angle estimator functions and the use of least squares artificial neural networks (LSANN), respectively. The SF force sensors are manufactured using methods developed by Meng Yee (Michael) Chuah of the MIT Biomimetic Robotics Laboratory (BRL). These SF force sensors are able to measure forces over several orders of magnitude, ranging from 10-2 to 103 N depending on the geometric properties of the sensor. Certain SF force sensor geometries provide different outcomes in terms of accuracy, sensitivity, maximum loading, torque measurement, and contact angle measurement. For example, sensors with decreased thickness displayed increased ability to measure smaller forces, and sensors that have outwardly cylindrical elastomer layers are capable of estimating torques. Additionally, of the SF force sensor geometries explored, sensors with hemispherical elastomer shapes had a lower (2-4%) root mean squared (RMS) error in both normal and shear force directions, and were most capable of measuring roll angles. These outcomes will be further detailed in this paper. The creation of these footpad sensors are a part of ongoing work aimed at developing low-cost, durable force sensors for use in the locomotion of dynamic robots. These force sensors would be beneficial in aiding robotic pose estimation and contact detection, thereby allowing traversal of more variable terrain. Implementation of these SF force sensor geometries was conducted by measuring standing and walking forces of the MIT Cheetah 3 quadruped robot and the little HERMES biped robot while each was outfitted with SF force sensing feet. Accurate normal force and roll angle estimates were able to be produced for hemispherical SF force sensors attached to Little HERMES. The MIT Cheetah 3 quadrupedal robot posed challenges to establishing a reliable force comparison. However, the SF force sensors (error of -17 N in flight) performed better then the Cheetah's proprioception (error of ±150 N in flight) when it came to distinguishing between stance and flight. It is postulated that this is due to decreased susceptibility to inertial noise. Future iterations of the SF force sensors developed in this thesis could enable legged robots to have more robust force measurement and pose estimation when undergoing dynamic locomotion. Such capabilities could allow legged robots to achieve performances matching those of animals and take on complex tasks to the benefit of our society.
by Juan Romero.
S.B.
27
Yukutake, Yohei. « Spatial change in the stress field around large earthquake faults ». 京都大学 (Kyoto University), 2006. http://hdl.handle.net/2433/144197.
Texte intégralRésumé :
Kyoto University (京都大学)0048
新制・課程博士
博士(理学)
甲第12114号
理博第3008号
新制||理||1448(附属図書館)
23950
UT51-2006-J109
京都大学大学院理学研究科地球惑星科学専攻
(主査)助教授 飯尾 能久, 教授 平原 和朗, 教授 橋本 学
学位規則第4条第1項該当
28
Cattò, Silvia <1990>. « Thermochronometric evidence of far-field stress transfer in continental collisions ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amsdottorato.unibo.it/8653/1/SC_Tesi_SilviaCatto%CC%80.pdf.
Texte intégralRésumé :
In this dissertation, two low-temperature thermochronometers [fission-track analysis on apatite and (U-Th)/He analyses on zircons] are applied on various tectonostratigraphic units from three collisional settings: (i) the Bitlis-Pütürge Massif (SE Turkey), (ii) the Lesser Caucasus (Georgia, Armenia, Azerbaijan), and (iii) the Strandja Massif (SE Bulgaria and NW Turkey). The aim of the study is to better understand the syn- and post-collisional thermochronological evolution of collisional orogens, thus elucidating the dynamics of stress partitioning and transmission during continental collisions. Another focal point of this study is to constrain better the timing of the Arabia-Eurasia collision in the area of its maximum indentation and clarify the overall evolution of the area. From a general viewpoint, our dataset for the Eurasian foreland north of the Arabia-Eurasia collision (the Bitlis-Pütürge Massif and the Lesser Caucasus region) suggest that the tectonic stresses related to the collision during mid-Miocene time were transmitted efficiently over large distances, focusing preferentially at rheological discontinuities located as far as the Lesser Caucasus and the Eastern Pontides. Since the late Middle Miocene a new tectonic regime is active as the westward translation of Anatolia is accommodating most of the Arabia-Eurasia convergence, thus decoupling the foreland from the orogenic wedge and precluding efficient northward stress transfer. In the Strandja Massif the mechanism of stress transmission was very different. The bulk of the massif has escaped significant Alpine-age deformation, which is recorded only in the northern sector. We argue that in the Strandja orogen the stress mostly bypassed the orogenic prism and focused on the Srednogorie rift basin to the north, rheologically weakened by previous Late Cretaceous back-arc extension.
29
CILIBERTI, MARIA GIOVANNA. « NUTRITION AND STRESS : A field study on the effects of diet on stress-related responses in sheep ». Doctoral thesis, Università di Foggia, 2014. http://hdl.handle.net/11369/331736.
Texte intégralRésumé :
Abstract
The aim of the present thesis was the study of the effects of nutrition on immune system of dairy ewes under different types of stressors.
The experiments were divided in four different trials. The first experiment was undertaken to evaluate the potential effects of phytosterols extracted from a microalga, intented to be used in sheep nutrition as feed supplements, on in vitro immunological responses of cells from dairy ewes. The second and the third trials were undertaken in order to evaluate the effects of PUFA supplementation on welfare and immune responses of sheep under heat stress. The second trial evaluated the effects of supplementation with polyunsaturated fatty acids from seaweed and flaxseed on welfare and in vivo immunological profile and HPA-axis activation during exposition of ewes to high ambient temperature. The third experiment studied the effects of supplementation with polyunsaturated fatty acids from seaweed and flaxseed on ex vivo inflammatory profile of cells from dairy ewes under high ambient temperature. The fourth trial evaluated the effects of supplementation with polyunsaturated fatty acids from flaxseed on immunological profile in dairy ewes during post partum.
In the first experiment peripheral blood mononuclear cells (PBMC) were isolated from sheep. PBMC were treated to determine cell proliferation and cytokine production with different sterols: ergosterol (E), a mixture of eleven Algae sterols extracted and purified from Dunaliella tertiolecta (Algae Extract, AE), a mixture of ergosterol and 7-dehydroporiferasterol extracted and purified from Dunaliella tertiolecta (Purified Extract, PE). Cytokine production (TNF-α, IL-
6, IL-1β, and IL-10) was evaluated after cell treatment with Concanavalin A (Con A) and lipopolysaccharide (LPS). The mixture of ergosterol and 7-dehydroporiferasterol extracted and purified from Dunaliella tertiolecta showed a suppressive effect on cell proliferation, and a reduction of pro-inflammatory cytokines production. Furthermore, a stimulatory effect on the production of the regulatory cytokine IL-10 was found. The immunosuppressive effect exerted by the mixture of ergosterol and 7-dehydroporiferasterol from Dunaliella tertiolecta was dose-dependent both in suppressing cell proliferation and in stimulating IL-10 production. Present results showed that the immunomodulatory and anti-inflammatory activities were more apparent in the purified extract characterized by the mixture of ergosterol and 7-dehydroporiferasterol, and might depend on the existence of a synergic effect of the structures of the two phytosterols. Furthermore, findings from our study suggest that the purified extract characterized by the mixture of ergosterol and 7-dehydroporiferasterol from Dunaliella tertiolecta could be used to reduce immune reactions resulting from inflammatory diseases in sheep production systems, and could have innovative implications on the modulation of sheep immune system when used as feed supplements.
The second experiment was carried out during the summer of 2012: thirty-two Comisana ewes were divided into four groups of eight. The FS group was supplemented with whole flaxseed, the AG group was supplemented with Ascophyllum nodosum, the FS+AG group was supplemented with a combination of flaxseed and Ascophyllum nodosum. The C group acted as a control. At 22 d of the experiment, cortisol concentrations in sheep blood were measured after an injection of adrenocorticotropic hormone (ACTH). Cellular immune response was evaluated by intradermic injection of phytohemagglutinin (PHA) at the beginning, and then at 15 d, and 30 d of the trial. Humoral response to ovalbumin (OVA) was measured at 0 d, 15 d, and 30 d. At 0 d, 15 d, and 30 d of the experiment, blood samples were collected from each ewe for determination of T-helper (Th)1 cytokines production (IL-12, and IFN-γ), and Th2 cytokine production (IL-10, IL-4, IL-13), and for determination of heat shock protein (HSP) 70 and 90 concentrations. Ewes supplemented with
flaxseed displayed greater cortisol concentrations and a long lasting cell-mediated immune response compared with the control and other experimental groups. Anti-OVA IgG concentrations rose in all groups throughout the trial, even though at 15 d ewes in the FS+AG group displayed the lowest anti-OVA IgG concentrations. IL-10 level increased in all groups throughout the experiment; the FS+AG group had the lowest IL-13 concentration at 15 d, and 30 d. HSP 70 increased in AG ewes at the end of the experiment, and decreased in FS ewes, while HSP 90 concentration increased in FS ewes compared with FS+AG ewes. Flaxseed supplementation was found to influence in vivo HPA activation in heat stressed sheep resulting in increased cortisol concentrations, probably to meet increased energy demand for thermoregulation. Flaxseed supplementation also supported Th1 response via a complex cross-talk between IL-10, IL-12, and IFN-γ production.
In the third experiment thirty-two Comisana ewes were divided into four groups of eight each. The FS group was supplemented with whole flaxseed, the AG group was supplemented with Ascophyllum nodosum, the FS+AG group was supplemented with a combination of flaxseed and Ascophyllum nodosum. The C group acted as a control. The third experiment was carried out during the summer of 2012. At 15 d of the experiment blood samples were collected in vacuum tubes from the jugular vein of sheep to isolate peripheral blood mononuclear cells (PBMC). Lymphocyte proliferation and production of interleuchin (IL)-6, IL-10, and IFN-γ were tested. PBMC from sheep fed Ascophyllum nodosum (AG) proliferated less and produced less IL-6 than PBMC from FS+AG and C groups. FS+AG cells produced lower levels of IL-10 than C cells, and higher IL-6 than AG and C cells. Results demonstrated that the supplementation with PUFA from different sources in sheep diet can influence their immunological responses under high ambient temperatures depending on the composition of fatty acid supplementation. In particular, synergistic effects of different PUFA, simultaneously administrated in the sheep diet, on activation of inflammation response have been observed.
In the fourth experiment twenty parturient Comisana ewes were divided into two groups of ten each. FS ewes were supplemented with whole flaxseed, the C ewes represented the control.
Peripheral blood samples from each ewe were collected from the jugular vein of ewes immediately before the first injection of OVA (0 d) and then at 7, 14, 21, 28, and 42 d from the day of parturition. Plasma samples were used to perform ELISAs to evaluate the anti-OVA IgG titers; at 0, 14, and 42d from parturition IL-1β, IL-6, IL-10 and TNF-α concentrations were measured in the plasma samples. The plasma anti-OVA IgG titres measured in this experiment displayed a reduced responsiveness to antigen stimulation both in C and in FS ewes. The production of IL-6 in C ewes registered an increase at parturition and then decreased throughout post partum; in FS ewes the levels of IL-6 registered at 14 d post partum were higher than those of IL-6 in C ewes; the same trend was observed for IL-10 production, which resulted two-fold higher at 14 d post partum in FS ewes than in C ewes. The lower concentration of IL-1β in FS ewes around parturition than in C ewes could be related to PUFA content of flaxseed, while the level of TNF-α in FS ewes at the end of post partum registered a decrease compared with levels of TNF-α in C ewes. This results demonstrated that flaxseed supplementation can contribute to reduce the duration of immune depression during post partum, by altering cytokines production, and improving ewes’ ability to respond to infections.
30
Zhang, Fengguo. « Determination of the stress field in polycrystalline materials by Laue microdiffraction ». Thesis, Paris, ENSAM, 2015. http://www.theses.fr/2015ENAM0020/document.
Texte intégralRésumé :
La microdiffraction Laue permet l'estimation des déformations élastiques à l'échelle du micron. La procédure d'analyse standard, bien établie, utilisée pour extraire les déformations élastiques des images de Laue est limitée par deux sources d'erreurs : la détermination de la positions des taches de Laue sur le détecteur, et la sensibilité aux paramètres de calibration du montage. Pour améliorer la procédure, nous avons développé une procédure appelée Laue-DIC qui utilise la très bonne résolution de la technique de corrélation d'images numériques (DIC). Cette méthode utilise, pour la détermination de l'incrément de déformation élastique et de rotation, le déplacement des pics entre deux configurations mécaniques, estimé par DIC, au lieu de leur position. Nous montrons que cette méthode donne un profil de contrainte en meilleur accord avec les solutions analytiques et numériques, pour des échantillons monocristallins déformés en flexion 4-points. Nous proposons également une méthode Laue-DIC améliorée, dans laquelle les paramètres de calibration sont estimés à chaque point de mesure, simultanément à la déformation élastique.En parallèle à la formulation de la méthode Laue-DIC (améliorée), nos efforts ont porté sur l'estimation de l'incertitude obtenue sur les déformations élastiques. Nous avons développé un modèle de bruit pour les images de Laue mesurées en rayonnement synchrotron, qui a été validé sur des séries de données, et qui nous a permis d'estimer les erreurs statistiques de la DIC, à partir d'images de Laue synthétiques. Ces erreurs ont ensuite été propagées dans la méthode Laue-DIC afin d'estimer les incertitudes sur les déformations élastiques, que l'on trouve en bon accord avec la fluctuation des contraintes locales estiméesLaue microdiffraction is a powerful technique to characterize the intragranular elastic strain field at the scale of micrometer. Although a standard procedure extracting elastic strain and crystal orientation from Laue image has been well-established, it can suffer from two sources of uncertainties: the determination of peaks' positions and the sensitivity to calibration parameters. In light of the high accuracy of digital image correlation (DIC), we developed the so-called Laue-DIC method which used the peaks' displacements measured by DIC instead of peaks' positions to determine the elastic strain increment and rotation between two mechanical configurations. This method has been proved more efficient than the standard procedure in terms of stress profiles of bended beam. We also developed the enhanced version of Laue-DIC. By using the term “enhanced”, we mean that we attempt to obtain both lattice matrices and calibration parameters of two configurations rather than solely the elastic strain increment and rotation from peaks' displacements.Aside from the formulation of Laue-DIC, we also developed a procedure of statistically estimating the errors of elastic strain/stress resulted from DIC errors and calibration accuracy. We have first validated a classical noise model, Poissonian-Gaussian model, from diffraction images acquired at synchrotron radiation facility. With the noise model, we could statistically estimate the DIC errors by synthesizing artificial spots. The estimated DIC errors were further transmitted into the errors of Laue-DIC through statistical tests
31
Tan, Mingan. « On the singular stress field at the interface of bimaterial systems ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq41516.pdf.
Texte intégral
32
Shope, Mitchell G. (Mitchell Grafton). « Strength characterization of wood to wood connections using stress field analysis ». Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/104245.
Texte intégralRésumé :
Thesis: M. Eng., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2016.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 69-70).
Minimizing construction cost and material usage are two dominant aspects in structural design. As a building material, timber presents a cheap, renewable option. However, current practice favors steel connections for wood structures. Wood to wood connections offer a solution to the minimization of steel connections. While some wood-only connections are referenced in timber codes, small modifications to these designs as well as a multitude of other possible connection types are yet to be characterized. This thesis analyzes wood to wood joints with stress fields. Stress field analyses may quickly and easily enable the design of timber joints and characterize the maximum loads they can handle. First, this thesis surveys and interconnects the theoretical concepts of wood behavior, plastic design, stress fields, and graphic statics. Additionally, this thesis tests these relationships empirically by load testing a designed double-birdsmouth connection and observing inconsistencies between the theoretical stress field model, code-required strength, and physical tests. The thesis shows that stress fields are a suitable design approach when considering the design of this wood-wood joint. The results also show that careful consideration must be attributed to the material properties of the wood as well as the possible failure modes. This thesis finally shows that shear failure should be checked in addition to compressive and tensile failure and provides a quick method to ensure a safe design.
by Mitchell G. Shope.
M. Eng.
33
Wolfe, Christopher Edward. « Damage accumulation in a gradient stress field in graphite/epoxy laminates ». Thesis, Massachusetts Institute of Technology, 1989. http://hdl.handle.net/1721.1/39360.
Texte intégral
34
Simmonds, Michael Patrick. « The stress field in a suspension of swimming model micro-organisms ». Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.615714.
Texte intégral
35
Nam, Taeksun. « Finite Analysis of Residual Stress Field Induced by Laser Shock Peening ». The Ohio State University, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=osu1216991714.
Texte intégral
36
Roman, Diana Christine. « Changes in local stress field orientation in response to magmatic activity / ». view abstract or download file of text, 2004. http://wwwlib.umi.com/cr/uoregon/fullcit?p3136443.
Texte intégral
37
Kese, Kwadwo O. « Relaxation and nanomechanical studies of the Vickers residual stress field in glass / ». Doctoral thesis, Stockholm, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-48.
Texte intégral
38
Yun, Kyyoul. « Magnetoelastic behavior of Ni-Fe alloys under magnetic field and tensile stress ». Kyoto University, 2009. http://hdl.handle.net/2433/123897.
Texte intégralRésumé :
Kyoto University (京都大学)0048
新制・課程博士
博士(エネルギー科学)
甲第14744号
エネ博第197号
新制||エネ||44(附属図書館)
UT51-2009-D456
京都大学大学院エネルギー科学研究科エネルギー変換科学専攻
(主査)教授 松本 英治, 教授 星出 敏彦, 教授 琵琶 志朗
学位規則第4条第1項該当
39
Sen, Debamoy. « Coupled Field Modeling of Gas Tungsten Arc Welding ». Diss., Virginia Tech, 2012. http://hdl.handle.net/10919/38820.
Texte intégralRésumé :
Welding is used extensively in aerospace, automotive, chemical, manufacturing, electronic and power-generation industries. Thermally-induced residual stresses due to welding can significantly impair the performance and reliability of welded structures. Numerical simulation of weld pool dynamics is important as experimental measurements of velocities and temperature profiles are difficult due to the small size of the weld pool and the presence of the arc. From a structural integrity perspective of welded structures, it is necessary to have an accurate spatial and temporal thermal distribution in the welded structure before stress analysis is performed. Existing research on weld pool dynamics simulation has ignored the effect of fluid flow in the weld pool on the temperature field of the welded joint. Previous research has established that the weld pool depth/width (D/W) ratio and Heat Affected Zone (HAZ) are significantly altered by the weld pool dynamics. Hence, for a more accurate estimation of the thermally-induced stresses it is desired to incorporate the weld pool dynamics into the analysis. Moreover, the effects of microstructure evolution in the HAZ on the mechanical behavior of the structure need to be included in the analysis for better mechanical response prediction. In this study, a three-dimensional model for the thermo-mechanical analysis of Gas Tungsten Arc (GTA) welding of thin stainless steel butt-joint plates has been developed. The model incorporates the effects of thermal energy redistribution through weld pool dynamics into the structural behavior calculations. Through material modeling the effects of microstructure change/phase transformation are indirectly included in the model. The developed weld pool dynamics model includes the effects of current, arc length, and electrode angle on the heat flux and current density distributions. All the major weld pool driving forces are included, namely surface tension gradient, plasma drag force, electromagnetic force, and buoyancy. The weld D/W predictions are validated with experimental results. They agree well. The effects of welding parameters (like welding speed, current, arc length, etc.) on the weld D/W ratio are documented. The workpiece deformation and stress distributions are also highlighted. The transverse and longitudinal residual stress distribution plots across the weld bead and their variations with welding speed and current are also provided. The mathematical framework developed here serves as a robust tool for better prediction of weld D/W ratio and thermally-induced stress evolution and distribution in a welded structure by coupling the different fields in a welding process.Ph. D.
40
Martin, Edward. « Determining the Amount of Irrigation Water Applied to a Field ». College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2006. http://hdl.handle.net/10150/147030.
Texte intégralRésumé :
3 pp.Critical to any irrigation management approach is an accurate estimate of the amount of water applied to a field. Too little water causes unnecessary water stress and can result in yield reductions. Too much water can cause water logging, leaching, and may also result in loss of yield. This publication discusses how to set the water amount and the time period, when taking the system's efficiency into consideration.
41
Martin, Edward C. « Determining the Amount of Irrigation Water Applied to a Field ». College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2011. http://hdl.handle.net/10150/239611.
Texte intégral
42
Schvezov, Carlos Enrique. « Temperature and dislocation stress field models of the LEC growth of gallium arsenide ». Thesis, University of British Columbia, 1986. http://hdl.handle.net/2429/27525.
Texte intégralRésumé :
The temperature fields and resulting stress fields have been calculated for a growing GaAs crystal produced by the LEC process. The calculations are based in a finite element numerical thermoelastic stress analysis. The calculated temperature fields have been compared to reported experimental measurements with good agreement. The stress fields have been used to calculate the resolved shear stresses, in the growing crystal, from which the dislocation density and distribution were determined.
Using the model the effects of a range of growth and environmental parameters on the dislocation density and distribution were determined. Theses parameters include crystal length, crystal diameter, cone taper, boron oxide thickness, gas pressure, solid/liquid interface shape, vertical temperature gradients and others. The results show that the temperature distribution in the gas surrounding the crystal, and the boron oxide thickness, were critical factors in determining the dislocation density and distribution in the crystal. The crystal radius, crystal length and interface curvature also strongly influenced the dislocation configuration. After crystal growth, the dislocation density at the end of the crystal was strongly influenced by the cooling procedure adopted. The dislocation distribution on cross-sections of the crystal exhibited two-fold, four-fold and eight-fold symmetry depending on growth and cooling conditions and position in the crystal.Applied Science, Faculty of
Mining Engineering, Keevil Institute of
Graduate
43
Reynolds, Scott. « Characterization and modelling of the regional in situ stress field of continental Australia ». Title page, contents and abstract only, 2001. http://web4.library.adelaide.edu.au/theses/09PH/09phr465.pdf.
Texte intégralRésumé :
Thesis (Ph.D.)--University of Adelaide, National Centre for Petroleum Geology and Geophysics, 2001.Copies of author's previously published works inserted. Additional resources are available on Web site. The CD-ROM edition has additional information. Bibliography: leaves 139-153. Also available in CD-ROM format.
44
Mann, Simon T. E. « The contemporary crustal stress field of the Browse Basin, North West Shelf, Australia / ». Title page, contents and abstract only, 2000. http://web4.library.adelaide.edu.au/theses/09SB/09sbm2823.pdf.
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Roy, Mark Philip. « Psychobiological reactivity and responses to stress : a laboratory and field study in firefighters ». Thesis, Royal Holloway, University of London, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.323878.
Texte intégral
46
Tulloch, Jo. « Stress in the role of the field social worker in a decentralised organisation ». Thesis, University of Sussex, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387387.
Texte intégral
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Sepasdar, Reza. « A Deep Learning Approach to Predict Full-Field Stress Distribution in Composite Materials ». Thesis, Virginia Tech, 2021. http://hdl.handle.net/10919/103427.
Texte intégralRésumé :
This thesis proposes a deep learning approach to predict stress at various stages of mechanical loading in 2-D representations of fiber-reinforced composites. More specifically, the full-field stress distribution at elastic and at an early stage of damage initiation is predicted based on the microstructural geometry. The required data set for the purposes of training and validation are generated via high-fidelity simulations of several randomly generated microstructural representations with complex geometries. Two deep learning approaches are employed and their performances are compared: fully convolutional generator and Pix2Pix translation. It is shown that both the utilized approaches can well predict the stress distributions at the designated loading stages with high accuracy.M.S.
Fiber-reinforced composites are material types with excellent mechanical performance. They form the major material in the construction of space shuttles, aircraft, fancy cars, etc., the structures that are designed to be lightweight and at the same time extremely stiff and strong. Due to the broad application, especially in the sensitives industries, fiber-reinforced composites have always been a subject of meticulous research studies. The research studies to better understand the mechanical behavior of these composites has to be conducted on the micro-scale. Since the experimental studies on micro-scale are expensive and extremely limited, numerical simulations are normally adopted. Numerical simulations, however, are complex, time-consuming, and highly computationally expensive even when run on powerful supercomputers. Hence, this research aims to leverage artificial intelligence to reduce the complexity and computational cost associated with the existing high-fidelity simulation techniques. We propose a robust deep learning framework that can be used as a replacement for the conventional numerical simulations to predict important mechanical attributes of the fiber-reinforced composite materials on the micro-scale. The proposed framework is shown to have high accuracy in predicting complex phenomena including stress distributions at various stages of mechanical loading.
48
Mildren, Scott. « The contemporary stress field of Australia's North West Shelf and collision=-related Tectonism / ». Title page, contents and abstract only, 1997. http://web4.library.adelaide.edu.au/theses/09PH/09phm641.pdf.
Texte intégral
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McLaughlin, John Gerard. « Renormalisation of the energy-momentum stress tensor for quantum fields on a curved background ». Thesis, University of Oxford, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.276530.
Texte intégral
50
Cesaretti, Juan Manuel. « Mechanical stress and stress compensation in Hall sensors ». Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/28202.
Texte intégral