To see the other types of publications on this topic, follow the link: Plastic properties.
Dissertations / Theses on the topic 'Plastic properties'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Plastic properties.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Mali, Sarvesh. "Study on plastic and mechanical properties of plastic stabilized returned plastic concretes containing supplementary cementitious materials." Thesis, Curtin University, 2016. http://hdl.handle.net/20.500.11937/1068.
Full textAbstract:
The growing concern for ready mix concrete industry is the disposal of returned unused concrete. In a plastic state, the concrete is a perishable product and the disposal of any unused concrete provides a set of challenges. However, little is known about the most effective parameters for recycling of returned plastic concrete without adversely affecting its properties. The present research has conducted laboratory trials to establish an optimal process for stabilizing returned plastic concretes using set-retarding admixture called “stabilizer”. Three types of cements, widely used in construction industry in Australia, are used in this research. The first is the ordinary Portland cement (OPC), while the rest are blended cements containing 25% class F fly ash and 65% slag as partial replacement of OPC.
2
Branch, James. "Plastic properties of fresh high strength concrete." Thesis, University of Surrey, 2001. http://epubs.surrey.ac.uk/842953/.
Full textAbstract:
This thesis describes the novel test techniques that were developed to measure the parameters associated with the plastic shrinkage, and subsequent possible plastic shrinkage cracking, of high strength concrete. The parameters measured during the first 24 hours after placing were the stress- strain relationship, negative pore pressure and free shrinkage strain development. The plastic behaviour of eight high strength concrete mixes was quantified and these mixes were then tested to assess their propensity towards plastic shrinkage cracking, using restrained ring tests. A review of the parameters associated with plastic shrinkage cracking was carried out. The general view was that as the particle size in a cement matrix gets smaller, then the negative pore pressures developed are greater and hence shrinkage increases. This meant that the presence of secondary cementing materials, of very small diameter, such as microsilica, in high strength concretes would explain their apparent susceptibility to plastic shrinkage cracking. Eight high strength concrete mixes were tested in exposed and sealed conditions. It was found that when tested in sealed conditions none of the parameters measured presented itself as the sole driving force behind plastic shrinkage or plastic shrinkage cracking. Also, when cured in sealed conditions, none of the mixes tested in the restrained ring test apparatus cracked. When tested in exposed conditions, the presence of wind had little effect on the stress-strain relationship of the mixes tested. However the presence of wind seemed to cause negative pore pressures to develop earlier than in the sealed samples and increased free shrinkage by 3 to 40 times depending on the mix. The samples that exhibited the highest free shrinkage strains, in exposed conditions, were the mixes that cracked when tested in the restrained shrinkage rings. The mixes that cracked all contained microsilica and these mixes did not crack when the same mixes were tested without microsilica. Polypropylene fibres were found to reduce the cracked area of the samples that cracked. The supplementary cementing materials used in this study were ground granulated blast furnace slag, metakaolin, microsilica and pulverised fuel ash.
3
Cheng, Hsiang-Nan, and Hsiang-Nan Cheng. "Diamond Turning Properties of Plastic Optical Materials." Thesis, The University of Arizona, 2017. http://hdl.handle.net/10150/625700.
Full textAbstract:
With sub-micrometric form accuracy and nanometer scale surface roughness, the diamond turning process provides a great solution of fast prototyping optical systems with aspheric or freeform surfaces. On the other hand, with relatively lower cost and lighter weight, optical plastics are now widely used in consumer products. To study and optimize the cutting parameters of the diamond turning process on optical plastics, a series of tests with different cutting parameters settings are conducted on seven different optical plastic materials: E48R, OKP1, OKP4, OKP4HT, PC, PMMA, and Rexolite 1422. The relationship between the surface roughness and optical plastic materials is found, and the optimized cutting parameters are recommended.
4
Kang, JiJun. "Determination of elastic-plastic and visco-plastic material properties from instrumented indentation curves." Thesis, University of Nottingham, 2013. http://eprints.nottingham.ac.uk/13509/.
Full textAbstract:
Instrumented indentation techniques at micro or nano-scales have become more popular for determining mechanical properties from small samples of material. These techniques can be used not only to obtain and to interpret the hardness of the material but also to provide information about the near surface mechanical properties and deformation behaviour of bulk solids and/or coating films. In particular, various approaches have been proposed to evaluate the elastic-plastic properties of power-law materials from the experimental loading-unloading curves. In order to obtain a unique set of elastic-plastic properties, many researchers have proposed to use more than one set of loading-unloading curves obtained from different indenter geometries. A combined Finite Element (FE) analysis and optimisation approach has been developed, using three types of indenters (namely, conical, Berkovich and Vickers), for determining the elastic-plastic material properties, using one set of ‘simulated’ target FE loading-unloading curves and one set of real-life experimental loading-unloading curves. The results obtained have demonstrated that excellent convergence can be achieved with the ‘simulated’ target FE loading-unloading curve, but less accurate results have been obtained with the real-life experimental loading-unloading curve. This combined technique has been extended to determine the elastic and visco-plastic material properties using only a single indentation ‘simulated’ loading-unloading curve based on a two-layer viscoplasticity model. A combined dimensional analysis and optimisation approach has also been developed and used to determine the elastic-plastic material properties from loading-unloading curves with single and dual indenters. The dimensional functions have been established based on a parametric study using FE analyses and the loading and linearised unloading portions of the indentation curves. It has been demonstrated that the elastic-plastic material properties cannot be uniquely determined by the test curves of a single indenter, but the unique or more accurate results can be obtained using the test curves from dual indenters. Since the characteristic loading-unloading responses of indenters can be approximated by the results of dimensional analysis, a simplified approach has been used to obtain the elastic-plastic mechanical properties from loading-unloading curves, using a similar optimisation procedure. It is assumed that the loading-unloading portions of the curves are empirically related to some of the material properties, which avoids the need for time consuming FE analysis in evaluating the load-deformation relationship in the optimisation process. This approach shows that issues of uniqueness may arise when using a single indenter and more accurate estimation of material properties with dual indenters can be obtained by reducing the bounds of the mechanical parameters. This thesis highlights the effects of using various indenter geometries with different face angles and tilted angles, which have not been covered previously. The elastic-plastic material parameters are estimated, for the first time, in a non-linear optimisation approach, fully integrated with FE analysis, using results from a single indentation curve. Furthermore, a linear and a power-law fitting scheme to obtain elastic-plastic material properties from loading-unloading indentation curves have been introduced based on dimensional analysis, since there are no mathematical formulas or functions that fit the unloading curve well. The optimisation techniques have been extended to cover time-dependent material properties based on a two-layer viscoplasticity model, has not been investigated before.
5
CHAKRABARTI, SEKHAR KUMAR. "INELASTIC BUCKLING OF GUSSET PLATES." Diss., The University of Arizona, 1987. http://hdl.handle.net/10150/184188.
Full textAbstract:
The strength and behavior of gusset plates in buckling is evaluated herein based on data from the experimental investigations conducted by other researchers and the analytical work presented herein. A set of design guidelines has been recommended through the review of the current practice. Representative single and double brace gusset plates normally adopted for connections with compressive bracing/diagonal members in braced frames and trusses, were modeled and analyzed using linear and nonlinear finite element methods to determine the buckling loads. The buckling analysis data along with the test data indicated the occurrence of inelastic buckling of the gusset plates. Current design practice and a set of formulas for determination of gusset plate thickness have been reviewed. A set of guidelines has been recommended for the design and evaluating gusset plate buckling loads.
6
Konduru, Srinivasa Raju. "Biodegradable and composting plastic. Properties and environmental impacts." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021.
Find full textAbstract:
Packaging waste forms a big a part of municipal solid waste and has caused increasing environmental considerations, leading to a strengthening of varied rules aimed toward reducing the amounts generated. Among different materials, a good vary of oil-based polymers is presently employed in packaging applications. These are nearly all non-biodegradable, and a few are troubled to recycle or apply because of being advanced composites having variable levels of contamination. Recently, important progress has been created within the development of biodegradable plastics, for the most part from renewable natural resources, to provide biodegradable materials with similar practicality thereto of oil-based polymers. The enlargement within these bio-based materials has many potential advantages for greenhouse gas balances and different environmental impacts over whole life cycles and in the use of renewable, instead of finite resources. it's supposed that use of biodegradable materials can contribute to sustainability and reduction within the environmental impact related to disposal of oil-based polymers.
The diversity of biodegradable materials and their variable properties makes it trouble to create straightforward, generic assessments like biodegradable product are all ‘good’ or petrochemical-based product are all ‘bad’. during this analysis I'm aiming to discuss the benefits of bioplastics and their substitution potential with respect to petroleum-based materials, the production of bioplastics using scratch and environmental impacts of its composting.
7
Bruce, J. M. "Self-diffusion and point defect studies in plastic crystals." Thesis, University of Strathclyde, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382256.
Full text
8
SALAMI, MOHAMMAD REZA. "CONSTITUTIVE MODELLING OF CONCRETE AND ROCKS UNDER MULTIAXIAL COMPRESSIVE LOADINGS." Diss., The University of Arizona, 1986. http://hdl.handle.net/10150/184202.
Full textAbstract:
Characterization of stress-deformation behavior of concrete and rocks have been a subject of active research for a long time. Linear elastic, nonlinear (piecewise) linear elastic, elastic-plastic and endochronic models have been proposed and used by various investigators and the literature on the subjects is very wide. A review of various models together with their implementation is numerical (finite element) procedures is presented in Ref. (77). The primary objective of the present study is to develop a generalized constitutive model based on the theory of plasticity. Although such a model can be used for a wide range of materials, in this dissertation its applications to plain concrete and rocks are emphasised. One of the main objectives of this dissertation is to study constitutive behavior of concrete and soapstone under multiaxial load histories by using a truly triaxial or multiaxial testing device. The truly triaxial device is capable of applying a general three-dimensional state of stress. Samples can be tested along any three dimensional stress path. Therefore, constitutive behavior of concrete and soapstone can be studied under all possible states of stress. The conventional, octahedral, proportional loading and circular stress test series are conducted using the truly triaxial cubical device. For meaningful results, samples with consistent initial properties are essential. In order to produce samples with uniform initial properties such as density, equipment and procedures are developed to standardize the sample preparation process. The test data is used to determine the material constants associated with the proposed constitutive model. The model is then verified by back-predicting the stress-strain curves obtained from the laboratory.
9
Swanson, Duane A. "Determination of the thermal properties of thin polymer films /." Online version of thesis, 1991. http://hdl.handle.net/1850/10789.
Full text
10
Luo, Li-Min. "Plastic instability and plastic flow properties and fracture of Al-2124 and Al-2124/SiCâ†p." Thesis, University of Reading, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.295282.
Full text
11
Li, Wei 1970 May 26. "Yield and geodesic properties of random elasto-plastic materials." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=115877.
Full textAbstract:
Two topics, i.e., the scale effects and the geodesics of random heterogeneous materials will be discussed in this work.When the separation of scales in random media does not hold, the representative volume element (RVE) of deterministic continuum mechanics does not exist in the conventional sense, and new concepts and approaches are needed. This subject is discussed here in the context of microstructures of two types - planar random chessboards, and planar random inclusion-matrix composites -- with microscale behavior being elastic-plastic-hardening (power-law). The microstructure is assumed to be spatially homogeneous and ergodic. Principal issues under consideration are those of yield and incipient plastic flow of statistical volume elements (SVE) on mesoscales, and the scaling trend of SVE to the RVE response on macroscale. Indeed, the SVE responses under uniform displacement (or traction) boundary conditions bound from above (respectively, below) the RVE response, and we show via extensive simulations in plane stress that the larger is the mesoscale, the tighter are both bounds. However, the mesoscale flows under both kinds of loading do not, in general, display normality. Also, with the limitation imposed by currently available computational resources, we do not recover normality (or even a trend towards it) when studying the largest possible SVE domains.
The second topic is the geodesic (i.e., shortest path) character of strain fields occurring in elasto-plastic response of planar inclusion-matrix composites. The composites' spatially random morphology is created by generating the disk centers through a sequential inhibition process based on a poisson point field in plane. Both phases (inclusions and matrix) are elastic-plastic-hardening with the matrix being more compliant and weaker than the inclusions, and perfect bonding everywhere. A quantitative comparison of a response pattern obtained by computational micromechanics with that found only by mathematical morphology indicates that (i) the regions of plastic flow are very close to geodesics, and (ii) a purely geometric, and orders of magnitude more rapid than by computational mechanics assessment of these regions is possible.
12
Beningfield, N. "The characterisation of the plastic properties of masonry mortars." Thesis, Kingston University, 2005. http://eprints.kingston.ac.uk/20738/.
Full textAbstract:
This programme of work was initiated as a result of recent major changes within Europe that have impacted upon the type of masonry mortars that are in use and the appropriate test procedures. A new suite oftest method standards, the EN 1015 series, has been issued by CEN over the last few years and supports two new mortar standards, BS EN 998-1 and BS EN 998-2, which are for plastering and rendering and masonry mortars respectively. In addition, there has been a large increase in the use of factory made mortar. Factory production, particularly as a dry mortar, leads itself to the production of more complex mortar formulations, and some mortars now contain as many as eight separate admixtures. These changes have lead to a large increase in the number of mortars that are highly air entrained, whilst the use of retarders and other admixtures in these mortars means that they frequently have pronounced thixotropic and other time dependant properties. All of these changes have in turn led to greater complexity in the fields of test methods and procedures. This thesis describes an investigation to define the properties of plastic mortar from first principles, then to compare these properties with the results produced by existing test methods to confirm ifthe latter were adequate. It was found that there were some properties for which several test methods existed, but some for which there were none. A test programme was then developed to investigate in detail and then to compare some relevant test methods, including new European ones and the older British ones that they replaced. Finally, two new, procedures were developed, one based on rheometry, one on the measurement of the early heat of hydration. Recommendations are made that these test procedures be further developed with a view to their adoption as standard tests.
13
Hardwick, S. T. "The origins and properties of transcrystalline layers in thermoplastics composites." Thesis, Brunel University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379414.
Full text
14
Chen, Xiaoxiao, and 陈晓晓. "Plastic deformation of silver micro-wires under uniaxial tension." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2011. http://hub.hku.hk/bib/B47048268.
Full text
15
Curtis, A. C. "Preparation and properties of oriented glass-filled thermoplastics." Thesis, University of Leeds, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379089.
Full text
16
左樂 and Le Zuo. "A statistical study on incipient plasticity of metals." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2007. http://hub.hku.hk/bib/B39558605.
Full text
17
Alameddine, Fadel 1964. "FLEXURAL STIFFNESS OF CIRCULAR REINFORCED CONCRETE COLUMNS (SLENDERNESS, ACI CODE, LOAD, DESIGN)." Thesis, The University of Arizona, 1986. http://hdl.handle.net/10150/276368.
Full text
18
Siu, Kai-wing, and 蕭啟穎. "Effects on plastic deformation by high-frequency vibrations on metals." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hub.hku.hk/bib/B50534087.
Full textAbstract:
The effect of softening due to vibrations induced on metals has been used in many industrial processes such as forming, machining and joining. These industrial applications utilize ultrasonic vibrations in addition to quasi-static stresses in order to deform metals more easily. The phenomenon of ultrasonic softening is also called the Blaha effect or acoustoplastic effect.
Besides the macro-scale softening due to ultrasonic vibrations imposed on quasi-static deformation stress, sub-micron level softening due to vibrations was also observed in nanoindentation experiments in recent years. These experiments made use of the oscillatory stresses of the vibrations provided by the continuous stiffness measurement (CSM) mode of nanoindentation. Lowering of loading and hardness data has been observed at shallow indent depths where the amplitude of vibration is relatively large.
Despite the common industrial usages of acoustoplastic effect and the observation of softening in CSM mode nanoindentation, the physical principle underlying is still not well understood. For acoustoplastic effect the existing understanding is usually one in which the ultrasonic irradiation either imposes additional stress waves to augment the quasi-static applied load, or causes heating of the metal. For the softening observed in CSM mode nanoindentation, the effect is either attributed to instrumental errors or enhancement of nucleation of dislocations which makes them move faster. Investigations on the link between microscopical changes and the softening have been rare.
In this thesis, indentation experiments in both macro and micro scales were performed on aluminium, copper and molybdenum samples with and without the simultaneously application of oscillatory stresses. Significant softening was observed, and the amount of softening from macro to micro scale indentation of similar displacement/amplitude ratios is similar. The deformation microstructures underneath the indents were investigated by a combination of cross-sectional microscopic techniques involving focused-ion-beam milling, transmission electron microscopy and crystal orientation mapping by electron backscattered diffraction. Electron microscopy analyses reveal subgrain formation under the vibrated indents, which implies intrinsic changes.
To further give physical insight into the phenomenon, dislocation dynamics simulations were carried out to investigate the interactions of dislocations under the combined influence of quasi-static and oscillatory stresses. Under a combined stress state, dislocation annihilation is found to be enhanced leading to larger strains at the same load history. The simulated strain evolution under different stress schemes also resembles closely certain experimental observations previously obtained. The discovery here goes far beyond the simple picture that the effect of vibration is merely an added-stress one, since here, the intrinsic strain-hardening potency of the material is found to be reduced by the oscillatory stress, through its effect on enhancing dislocation annihilation.
The experimental and simulation results collectively suggest that simultaneous application of oscillatory stress has the ability to enhance dipole annihilation and cause subgrain formation. The superimposed oscillatory stress causes dislocations to travel longer distances in a jerky manner, so that they can continuously explore until dipole annihilation. In addition, microscopic observations showed that subgrain formation and reduction in dislocation density generally occurred in different metals when stress oscillations were applied. These suggest that the intrinsic oscillation-induced effects of softening and dislocation annihilation are a rather general phenomenon occurring in metals with different stacking fault energies and crystal structures.published_or_final_version
Mechanical Engineering
Doctoral
Doctor of Philosophy
19
Armstrong, D. E. J. "Measuring elastic, plastic and fracture properties using micro-cantilever testing." Thesis, University of Oxford, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.526568.
Full text
20
Mokwena, Kereilemang Khanah. "Barrier properties of ethylene vinyl alcohol films in thermal processing." Pullman, Wash. : Washington State University, 2010. http://www.dissertations.wsu.edu/Dissertations/Spring2010/k_mokwena_050310.pdf.
Full text
21
Schubak, Robert Brian. "Nonlinear rigid-plastic analysis of stiffened plates under blast loads." Thesis, University of British Columbia, 1991. http://hdl.handle.net/2429/31482.
Full textAbstract:
The large ductile deformation response of stiffened plates subjected to blast loads is investigated and simplified methods of analysis of such response are developed. Simplification
is derived from modelling stiffened plates as singly symmetric beams or as grillages thereof. These beams are further assumed to behave in a rigid, perfectly plastic manner and to have piecewise linear bending moment-axial force capacity interaction relations, otherwise known as yield curves.
A blast loaded, one-way stiffened plate is modelled as a singly symmetric beam comprised
of one stiffener and its tributary plating, and subjected to a uniformly distributed line load. For a stiffened plate having edges fully restrained against rotations and translations,
both transverse and in-plane, use of the piecewise linear yield curve divides the response of the beam model into two distinct phases: an initial small displacement phase wherein the beam responds as a plastic hinge mechanism, and a final large displacement phase wherein the beam responds as a plastic string. If the line load is restricted to be a blast-type pulse, such response is governed by linear differential equations and so may be solved in closed form. Examples of a one-way stiffened plate subjected to various blast-type pulses demonstrate good agreement between the present rigid-plastic formulation and elastic-plastic beam finite element and finite strip solutions.
The response of a one-way stiffened plate is alternatively analysed by approximating it as a sequence of instantaneous mode responses. An instantaneous mode is analogous to a normal mode of linear vibration, but because of system nonlinearity exists for only the instant and deformed configuration considered. The instantaneous mode shapes are
determined by an extremum principle which maximizes the rate of change of the stiffened plate's kinetic energy. This approximate rigid-plastic response is not solved in closed form but rather by a semi-analytical time-stepping algorithm. Instantaneous mode solutions compare very well with the closed-form results.
The instantaneous mode analysis is extended to the case of two-way stiffened plates, which are modelled by grillages of singly symmetric beams. For two examples of blast loaded two-way stiffened plates, instantaneous mode solutions are compared to results from super finite element analyses. In one of these examples the comparison between analyses is extremely good; in the other, although the magnitudes of displacement response
differ between the analyses, the predicted durations and mechanisms of response are in agreement.
Incomplete fixity of a stiffened plate's edges is accounted for in the beam and grillage models by way of rigid-plastic links connecting the beams to their rigid supports. Like the beams, these links are assumed to have piecewise linear yield curves, but with reduced bending moment and axial force capacities. The instantaneous mode solution is modified accordingly, and its results again compare well with those of beam finite element analyses.
Modifications to the closed-form and instantaneous mode solutions to account for strain rate sensitivity of the panel material are presented. In the closed-form solution, such modification takes the form of an effective dynamic yield stress to be used throughout the rigid-plastic analysis. In the time-stepping instantaneous mode solution, a dynamic yield stress is calculated at each time step and used within that time step only. With these modifications in place, the responses of rate-sensitive one-way stiffened plates predicted by the present analyses once again compare well with finite element and finite strip solutions.Applied Science, Faculty of
Civil Engineering, Department of
Graduate
22
Nanda, Atul. "Finite element analysis of elastic-plastic anisotropic soils." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/53650.
Full textAbstract:
Elastic-plastic stress·strain models are developed for initially anisotropic soils. The models are developed for both total stress (undrained) analyses and for effective stress (drained) analyses. For anlsotroplc undralned coheslve soils under monotonic loading an elastic-plastic isotropic-hardening model is developed. For complex loading conditions the model is extended using multisurface plasticity. For effective stress analyses of soils, the Cam-Clay model concepts are generalized for initially anisotropic soils. Both isotropic and anisotropic hardening are used in the model. The behavior of the models is investigated under several loading conditions and some comparisons are made with experimental triaxial data. A nonlinear three-dimensional finite element program is developed in which the models are implemented. An updated Lagrangian large displacement analysis is also included. The constitutive models developed are used to investigate the influence of initial anisotropy on the bearing capacity, deformation and pore pressure development under footings in both plane-strain and three dimensional conditions. It is found that for the range of anisotropy encountered in the field, the deformation and bearing capacity are significantly different.Ph. D.
23
Collins, Steve Alan. "Development and implementation of a hypoelastic constitutive theory to model the behavior of sand." Diss., Georgia Institute of Technology, 1988. http://hdl.handle.net/1853/21282.
Full text
24
Cheng, Bingqing, and 程冰清. "Computer simulations of crystal plasticity at different length scales." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2014. http://hdl.handle.net/10722/206446.
Full textAbstract:
Crystal plasticity has been an active research field for several decades. The crystal plasticity of the bulk materials has its key relevance in the industrial process. Besides, the plasticity of nano-sized materials becomes a topic attracting a lot of interest recently.
In the Part I of the thesis, molecular dynamics (MD) simulations were used to study the plasticity of small nanoparticles. Firstly, the coalescence process of Cu nanoparticles was explored. It was found that a peculiar type of five-fold twins in the sintered products were formed via an unseen before dislocation-free process involving a series of shear waves and rigid-body rotations. Secondly, a similar study on the heating of a single nanoparticle was conducted. The same dislocation-free shear wave mechanism was spotted again. In this mechanism, a cluster of atoms rearranges in a highly coordinated way between different geometrical configurations (e.g. fcc, decahedral, icosahedral) without involving dislocations. Thirdly, simulations on the sintering of many nanoparticles were performed, and the governing processes during the consolidation were discussed. The findings in this part of the thesis can provide some guidance for controlling the motifs of nanoparticles.
In Part II of the thesis, the emphasis was switched to the crystal plasticity at larger spatial and temporal scales. A dislocation density-based model was developed in our research group. This model employs a dynamics formulation in which the force on each group of dislocation density is calculated with the Taylor and mutual elastic interactions taken into account. The motion of the dislocation densities is then predicted using a conservative law, with annihilation and generation considered. The new dislocation density-based model was used in this work to simulate the plastic deformation of single crystals under ultrasonic irradiation. Softening during vibrations as well as enhanced cell formation was predicted. This is the first simulation effort to successfully predict the cell formation phenomenon under vibratory loadings.published_or_final_version
Mechanical Engineering
Master
Master of Philosophy
25
TOUFIGH, MOHAMMAD MOHSEN. "BEHAVIOR OF UNSATURATED SOIL AND ITS INFLUENCE ON SOIL - SOIL INTERACTION AT AN INTERFACE." Diss., The University of Arizona, 1987. http://hdl.handle.net/10150/184224.
Full textAbstract:
The interface failure between caps and natural soil in trenches containing buried low level nuclear waste material was investigated in this study. The Casa Grande Highway Farm (CGHF) soil was used for the entire investigation. This soil is described as being a silty sand with approximately 23% by weight passing sieve No. 200. Other preliminary testing was performed on the same soil. Isotropically consolidated drained (CID) tests were performed on the laboratory compacted samples at different degree of saturation including fully saturated specimens. Suction pressure was measured in the laboratory by adopting pressure plate extractor and compared with determined effective suction in triaxial testing. A generalized failure equation, in term of strength parameters and suction pressure, was defined for all degrees of saturation. The consideration of unsaturated soil sets the current modified model apart from previous bounding surface which only allows use of fully saturated cohesive soil. The saturated material constants associated with the model are identified. These new constants are obtained from a generalized failure equation. The model was then verified by comparing predictions with other laboratory tests which are not used in the calibration. Generally a good agreement between the model and test results was found for stress-strain, stress path and volumetric strain response at different degrees of saturation. Extensive interface tests were performed in the conventional direct shear machine with some modification. Similar to trench cap soil and natural soil in the field, the test specimens were prepared at different degrees of saturation and density (compaction effort). Comparisons were made for the effects of magnitude of normal load, degree of saturation, density, compaction effort, moisture migration and dissimilar bodies density. An interface element and the modified bounding surface model and elasticity model was used in a finite element program to predict the interface response for the laboratory results and actual field problems. Material parameters related to the interface were identified and good predictions were observed for the interface behavior.
26
Southworth, Roger Kevin 1961. "SPATIAL VARIATION MODELING OF REGULARLY SPACED SOIL PROPERTY DATA IN ONE DIMENSION (TIME SERIES ANALYSIS)." Thesis, The University of Arizona, 1986. http://hdl.handle.net/10150/276870.
Full text
27
Gzyl, Michael. "Improving mechanical properties of a magnesium alloy by severe plastic deformation." Thesis, University of Strathclyde, 2014. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=24213.
Full textAbstract:
Magnesium alloys are very promising materials for automotive and aerospace applications due to their low density. The market of medical implants (e.g. temporary orthopaedic and cardiovascular implants) is another field of possible applications of magnesium alloys since they can completely dissolve within human body without causing any major health issues. Unfortunately, magnesium alloys have been well-known from their low formability at room temperature and poor corrosion resistance. The aim of the current work was to improve mechanical properties of a magnesium alloy by incremental equal channel angular pressing (I-ECAP). The goal of the process is to refine grain structure of a continuous bulk metallic billet without changing its dimensions. In the current work, the most popular wrought magnesium alloy AZ31B was subjected to I-ECAP for the first time to confirm potential of the method for industrial production of innovative lightweight materials. The process window was determined on the basis of I-ECAP experiments conducted with various process parameters (temperature, processing route, initial grain size of the alloy). Additionally, various microstructural characterization methods, including ex situ and in situ analyses, were incorporated in this work to show a relation between the grain size and the deformation mechanisms occurring in the alloy. It was found that mechanical properties of AZ31B can be tailored to a specific application by using different process parameters. It was shown that yield strength can be increased from 165 MPa to 290 MPa when temperature of I-ECAP is reduced to 150°C. Moreover, room temperature ductility of the produced material can exceed 40% when a combination of I-ECAP and subsequent heat treatment is applied. The results of the work confirmed that I-ECAP could be considered as the useful method for producing advanced lightweight metallic materials with a potential for industrial applications.
28
Masri, Haji Mohammad Khairul Ja'afar Awang Haji. "Elastic properties and local buckling of pultruded fibre reinforced plastic profiles." Thesis, Cardiff University, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.548179.
Full text
29
Savini, Gianluca <1972>. "Theory of plastic and elastic properties of graphite and silicon carbide." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2007. http://amsdottorato.unibo.it/352/1/Savini-Thesis.pdf.
Full text
30
Savini, Gianluca <1972>. "Theory of plastic and elastic properties of graphite and silicon carbide." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2007. http://amsdottorato.unibo.it/352/.
Full text
31
Berrada, Kamal. "An experimental investigation of the plastic buckling of aluminum plates /." Thesis, McGill University, 1985. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=63160.
Full text
32
Pungthong, Viriya. "Mechanical properties of polymeric packaging films after radiation sterilization /." Online version of thesis, 1990. http://hdl.handle.net/1850/11179.
Full text
33
Adhikary, Kamal Babu. "Development of Wood Flour-Recycled Polymer Composite Panels As Building Materials." Thesis, University of Canterbury. Chemical and Process Engineering, 2008. http://hdl.handle.net/10092/1795.
Full textAbstract:
Wood plastic composites (WPCs) were made using matrices of recycled high-density polyethylene (rHDPE) and polypropylene (rPP) with sawdust (Pinus radiata) as filler. Corresponding WPCs were also made using virgin plastics (HDPE and PP) for comparison with the recycled plastic based composites. WPCs were made through melt compounding and hot-press moulding with varying formulations based on the plastic type (HDPE and PP), plastic form (recycled and virgin), wood flour content and addition of coupling agent. The dimensional stability and mechanical properties of WPCs were investigated. Durability performances of these WPCs were studied separately, by exposing to accelerated freeze-thaw (FT) cycles and ultraviolet (UV) radiation. The property degradation and colour changes of the weathered composites were also examined. Dimensional stability and flexural properties of WPCs were further investigated by incorporation of nanoclays in the composite formulation. To understand the changes in WPCs stability and durability performance, microstructure and thermal properties of the composites were examined. Two mathematical models were developed in this work, one model to simulate the moisture movement through the composites in long-term water immersion and the other model to predict the temperature profile in the composites during hot-press moulding.
Both rHDPE and rPP matrix based composites exhibited excellent dimensional stability and mechanical properties, which were comparable to those made from virgin plastics. Incorporation of maleated polypropylene (MAPP) coupling agent in composite formulation improved the stability and the mechanical properties. The incorporation of 3 wt. % MAPP coupling agent to WPCs showed an increase in tensile strength by 60% and 35 %, respectively, for the rHDPE based and rPP based composites with 50 wt. % wood flour. Scanning electron microscopy (SEM) images of the fractured surfaces of WPCs confirmed that the MAPP coupling improved the interfacial bonding between the plastic and the wood filler for both series of composites. Long-term water immersion tests showed that the water transport mechanism within the WPCs follows the kinetics of Fickian diffusion.
Dimensional stability and flexural properties of the WPC were degraded after 12 accelerated FT cycles as well as 2000 h of UV weathering for both recycled and virgin HDPE and PP based composites. However, the MAPP coupled composites had improved stability and flexural property degradation. The surface of the weathered composites experienced a colour change, which increased with the exposure time. The MAPP coupled composites exhibited less colour change as compared to non-coupled composites. Regarding the effect of the plastic type, the PP based composites experienced higher colour change than those based on HDPE. With weathering exposure, flexural strength and stiffness of the WPCs were decreased, but elongation at break was increased regardless of plastic type and wood flour content. MAPP coupled rPP and rHDPE based UV weathered WPCs lowered the degradation of stiffness by 50% and 75%, respectively compared to non-coupled WPCs. SEM images of the fractured surfaces of FT and UV weathered WPCs confirmed a decrease in the interfacial bonding between the wood flour and matrix. Thermal properties of weathered composites changed with weathering, but the extent of the changes depended on WPCs formulation and matrix type.
From the experimental studies on nanoclay-filled rHDPE composites, it is found that stability, flexural properties of WPCs could be improved with an appropriate combination of coupling agent, and nanoclay contents processed by melt blending. Incorporation of 1-5 wt. % nanoclay in the maleated polyethylene (MAPE) coupled wood plastic composite improved the dimensional stability and flexural properties. The thermal properties changed with the addition of nanoclay and MAPE in WPCs. In this work, a hot press-moulding model was proposed based on the one-dimensional transient heat conduction to predict the temperature profile of the WPCs during hot pressing cycle. The results from this work clearly show that rHDPE and rPP can be successfully used to produce stable and strong WPCs, which properties and performances are similar to or comparable to composites made of wood and virgin plastics. Therefore, WPCs based on recycled PP and HDPE matrix could have potential to use as construction materials.
34
Yapici, Guney Guven. "Severe plastic deformation of difficult-to-work alloys." Thesis, Texas A&M University, 2004. http://hdl.handle.net/1969.1/531.
Full textAbstract:
The present work aims to reveal the microstructural evolution and post-processing mechanical behavior of difficult-to-work alloys upon severe plastic deformation. Severe plastic deformation is applied using equal channel angular extrusion (ECAE) where billets are pressed through a 90o corner die achieving simple shear deformation. Three different materials are studied in this research, namely Ti-6Al-4V, Ti-6Al-4V reinforced with 10% TiC and AISI 316L stainless steel. Microstructure and mechanical properties of successfully extruded billets were reported using light microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), tension and compression experiments and microhardness measurements. The effects of extrusion conditions (temperature and processing route) on the microstructure and mechanical properties are investigated. The underlying mechanisms responsible for observed mechanical behaviors are explored. It is seen that ECAE shear deformation leads to refinement in α plates and elimination of prior β boundaries in Ti-6Al-4V. Decreasing extrusion temperature and increasing number of passes decreases α plate size and grain size. Refined α grain size leads to a significant increase in tensile and compressive flow stresses at room temperature. Texture produced by ECAE has a pronounced effect on mechanical properties. Specifically it leads to tension/compression asymmetry in flow strengths and strain hardening coefficients may be described by the activation of differing slip systems under tension and compression loading. ECAE of Ti-6Al-4V+10%TiC samples also improved mechanical properties due to α plate size refinement. Nevertheless, further extrusion passes should be carried out for tailoring reinforcement size and distribution providing optimum strength and ductility. ECAE deformation of AISI 316L stainless steel at high homologous temperatures (0.55 to 0.60 Tm) results in deformation twinning as an effective deformation mechanism which is attributed to the effect of the high stress levels on the partial dislocation separation. Deformation twinning gives rise to high stress levels during post-processing room temperature tension and compression experiments by providing additional barriers to dislocation motion and decreasing the mean free path of dislocations. The highest tensile flow stress observed in the sample processed at 700 oC following one pass route A was on the order of 1200 MPa which is very high for 316L stainless steel. The ultimate goal of this study is to produce stabilized end microstructures with improved mechanical properties and demonstrate the applicability of ECAE on difficult-to-work alloys.
35
Toledo, García Gustavo A. "High temperature compression testing of hardened steels for plasticity behavior modeling." Thesis, Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/16909.
Full text
36
永正, 邵., and Yongzheng Shao. "Study on the effects of matrix properties on the mechanical properties of carbon fiber reinforced plastic composites." Thesis, https://doors.doshisha.ac.jp/opac/opac_link/bibid/BB12902982/?lang=0, 2015. https://doors.doshisha.ac.jp/opac/opac_link/bibid/BB12902982/?lang=0.
Full textAbstract:
It was found that a significant improvement of mechanical properties of CFRPs can be achieved by the adjustment of the matrix properties such as toughness and CF/matrix adhesion via the chemical modification, as well as the physical modification by a small amount of cheap and environment-friendly nano fibers. Based on investigation of fracture mechanisms at macro/micro scale, the effects of matrix properties and nano fiber on the mechanical properties of CFRP have been discussed. Subsequently, the relationship has been characterized by a numerical model to show how to modulate the parameters of the matrix properties to achieve excellent fatigue properties of CFRP.博士(工学)
Doctor of Philosophy in Engineering
同志社大学
Doshisha University
37
Savostyanova, Natalia, and Valeriya Velichko. "Plastic card frauds, a survey of current relevant card and system properties." Thesis, Linköping University, Department of Electrical Engineering, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-2424.
Full textAbstract:
Recently the society has been turning from the use of paper-based technologies to plastic cards in certain spheres of our life. With the emergence and proliferation of high technologies we cannot content with the security provided bypaper only. Therefore the society has chosen plastic to protect its information because it offers far more security based not only on human perception but also on machine-readable elements.
The number of plastic cards in circulation in different spheres of our everyday life increases constantly. They replace money, documents and allow easy and safe access to some services. In spite of its security the plastic card however is subjected to fraud.
Plastic card fraud results in significant losses for the various industries. Since the first appearance of plastic cards methods of committing fraud have changed dramatically. Now there is a wide range of high technologies at the disposal of criminals as well as card manufacturers.
Therefore we have put the great emphasize of this work on the analysis of the most common card technologies in the Plastic Card World, the magnetic stripe and the chip, existing crimes and main means of their committing. And we also have revealed the weak and strong sides of the prevention techniques, which are currently in use.
38
Buzit, Sebastien. "Evolution of crystallographic textures and TRIP effects in stainless steel AISI 304." Thesis, Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/19584.
Full text
39
Li, Jianjun, and 李建军. "Theoretical modelling and numerical simulation of plastic deformation of nanostructured materials with high strength and ductility." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hub.hku.hk/bib/B50605707.
Full textAbstract:
Nanostructured materials have attracted intensive scientific interests during the past two decades due to their outstanding physical and mechanical properties. However, the brittleness of nanostructured materials posed a great challenge for their engineering applications. Recently, several strategies were successfully adopted to produce nanostructured materials with both high strength and ductility such as surface-nanocrystallized (SNC) materials, nanocrystalline materials with stress-induced nanograin growth and nanotwinned metals. A lot of molecular dynamics (MD) simulations, modelling and experiments have been conducted to investigate the deformation mechanisms and the correlated exceptional mechanical properties and considerable progress has been made. However, some problems remain unsolved. For example, the complicated structure of SNC materials due to its grain size gradient (GSG) surface layer makes it difficult to establish a quantitative model for prediction of their strength and ductility; the main mode of nanograin growth in nanostructured materials, i.e., shear-coupled migration of grain boundaries (GBs), was experimentally observed as contributing to their enhanced ductility, but the mechanism of the enhancement remains unclear. In addition, there exist contradictory results for the grain size dependence of transitional twin thickness that corresponds to the maximum strength of nanotwinned metals. All these issues should be addressed to gain a better understanding of the mechanism-ductility correlation in order to provide some guidelines for designing lighter, stronger and ductile nanostructured materials. Therefore, an attempt was made to study the plastic deformation of nanostructured materials with high strength and ductility by theoretical modelling and numerical simulations.
Firstly, the enhanced balance of strength and ductility of SNC materials was studied using a combination of theoretical analysis and finite element simulation. A criterion was established for determining the ductility of SNC materials. The results obtained showed that the ductility of a SNC sample could be comparable to that of its coarse-grained counterpart, while it simultaneously possessed a much higher strength than that of the latter if optimal GSG thickness and topmost phase grain size were adopted. Then a dislocation-density-based model was proposed to quantitatively predict the plastic deformation of SNC materials; the stress-driven nanograin growth was also incorporated in the said model. The capability of the model in predicting the strength and work hardening of SNC materials was validated by the existing experimental results. Thirdly, physical models for shear-coupled migration of GBs in nanostructured materials were developed to explain the general coupling between the shear and the normal migration of GBs observed in MD simulations and experiments. The coupled migration process was found to be a general and effective toughening mechanism in nanostructured materials. Moreover, our study showed that the shear-coupled migration is able to enhance the intrinsic ductility considerably when it cooperates with GB sliding. Finally, an elastic-viscoplastic constitutive model based on the competition of intra-twin and twin-boundary-mediated deformation mechanisms was proposed to predict the grain size dependent transitional twin thickness of nanotwinned metals. A linear relation between the transitional twin thickness and the grain size was predicted, which was in excellent agreement with the results obtained from MD simulations and experiments available in the literatures.published_or_final_version
Mechanical Engineering
Doctoral
Doctor of Philosophy
40
Scott, J. A. "A study of the effect of process variables on the properties of rotationally moulded plastic articles." Thesis, Queen's University Belfast, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381175.
Full text
41
Pruell, Christoph. "Generation and detection of lamb waves for the characterization of plastic deformation." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/26479.
Full textAbstract:
Thesis (M. S.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2008.Committee Chair: Jacobs, Laurence; Committee Member: Kim, Jin-Yeon; Committee Member: Qu, Jianmin. Part of the SMARTech Electronic Thesis and Dissertation Collection.
42
Phung, Kent, and Charles Chu. "Adhesives for Load-Bearing Timber-Glass Elements : Elastic, plastic and time dependent properties." Thesis, Linnéuniversitetet, Institutionen för bygg- och energiteknik (BE), 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-27386.
Full textAbstract:
This thesis work is part of an on-going project regarding load-bearing timber glass composites within the EU program WoodWisdom-Net. One major scope of that project is the adhesive material between the glass and timber parts. The underlying importance of the bonding material is related to the transfer of stress between the two materials – the influence of the adhesive stiffness and ductility on the possibility of obtaining uniform stress distributions. In this study the mechanical properties of two different adhesives are investigated, an epoxy (3M DP490) and an acrylate (SikaFast 5215). The differences of the adhesives lay in dissimilar stiffness, strength and viscous behaviour. In long term load caring design is important to understand the materials behavior under a constant load and a permanent displacement within the structure can cause major consequences. Therefore the main aim in this project is to identify the adhesives strength, deformation capacity and possible viscous (time dependent) effects. Because of the limitation of equipment and time this study is restricted to only three different experiments. Three different types of tensile tests have been conducted: monotonic, cyclic relaxation tests.The results of the experiments show that 3M DP490 has a higher strength and a smaller deformation capacity as compared to the SikaFast 5215. Thus, the SikaFast 5215 is more ductile. The 3M DP490 exhibits a lower loss of strength under constant strain (at relaxation). SikaFast 5215 showed also a large dependency of strain level on the stress loss in relaxation.
43
Wang, Lei. "Study on the characterization of mechanical properties of viscoelastic-plastic materials by nanoindentation." Thesis, University of Warwick, 2014. http://wrap.warwick.ac.uk/67680/.
Full textAbstract:
The aim of this PhD work is to develop a novel and effective instrument to characterize the mechanical properties of viscoelastic material. The principle of this system is based on nanoindentation technique, which is widely used in recent years to explore the mechanical properties of various materials. However, quite a few studies demonstrated that the determination of mechanical properties of viscoelastic material by using the standard Oliver Pharr method would lead to incorrect results. Based on this issue, a new improved tribological probe microscopy (TPM) system was established to carry out the investigation of mechanical properties of viscoelastic materials. Materials including polytetrafluoroethylere (PTFE), styrene rubber and nitrile rubber were measured under quasi-static mode of nanoindentation. The inaccurate results proved that static indentation analyzed by the Oliver Pharr method is not suitable for current work. In addition, dynamic indentation was performed to measure these samples. The results demonstrated that it is a good approach to explore time-dependent properties of polymer samples. The dynamic method offers more abundant viscous information. Moreover, another measurement function was added in this facility to perform creep nanoindentation on viscoelastic samples. It enables to generate instant and infinite modulus as well as time constant. The comparison between the results obtained by dynamic and creep indentation reveals that the more physical element should be considered to bridge the gap between these two approaches. Extra works focus on the relationship between surface topography and its mechanical properties. Finite element simulation as well as actual experiments were performed to investigate the tilt effect on the results of mechanical properties. The results revealed that the standard Oliver Pharr method underestimated the contact area, which will result in overestimating the hardness and elastic modulus of engineering materials. Above all, this study proved the ability of our home made facility to further explore the viscoelastic material. More importantly, it will pave a new way for the investigation of the relationship between the surface topography and viscous property of soft matter including various biomaterials in the near future.
44
Latta, IV Leigh C. "Plastic and Genetic Determination of Population, Community, and Ecosystem Properties in Freshwater Environments." DigitalCommons@USU, 2010. https://digitalcommons.usu.edu/etd/618.
Full textAbstract:
The hierarchy of biological organization, from molecules to ecosystems, describes the relationships among various biological systems. Of particular interest is assessing how the factors that primarily determine the nature of one hierarchical level also have transcendent qualities that affect the ecology and evolution of higher hierarchical levels. The goal of this dissertation was to use a bottom-up approach to examine the transcendent effects of two factors that strongly determine the nature of their associated level of biological organization. The first, phenotypic plasticity, is a primary factor that determines the phenotype of an individual. The second factor, genetic diversity, largely determines the phenotypic distributions associated with populations. Controlled laboratory experiments on taxa from a freshwater tri-trophic food web were employed to examine the transcendent effects of phenotypic plasticity and genetic diversity on the biological hierarchy because relationships between individuals and populations from different trophic levels are well documented for numerous freshwater species. The results show that phenotypic plasticity can induce changes in population means and variances that promote population persistence and evolvability, and that plasticity provides a mechanistic explanation of community stability in response to changing environments. Similarly, genetic diversity may act as a signal that induces phenotypic plasticity in individuals, modulates community richness and ecosystem properties, and suggests a potential mechanism for the changes in biodiversity. Thus, results from this dissertation show that plasticity and genetic variation can shape the attributes of other biological groups higher in the biological hierarchy, and, in some cases, may also provide a mechanistic explanation for variability observed in higher levels of the biological hierarchy. These results highlight the importance of integrating traditionally disparate biological disciplines and may help to unify biology as a field.
45
To, Chiu-yin, and 杜昭彥. "A unified elasto-plastic model for saturated loosely compacted completely decomposed granite." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2008. http://hub.hku.hk/bib/B40203554.
Full text
46
Liu, Tao. "Novel methods for determining the optical constants of anisotropic polymer films -- new application of prism wave-guide coupling." Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/8602.
Full text
47
Rodeheaver, Bret Alan. "Open-celled microcellular themoplastic foam." Thesis, Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/18914.
Full text
48
HASHMI, QUAZI SARWAR EHSAN. "NONASSOCIATIVE PLASTICITY MODEL FOR COHESIONLESS MATERIALS AND ITS IMPLEMENTATION IN SOIL-STRUCTURE INTERACTION." Diss., The University of Arizona, 1987. http://hdl.handle.net/10150/184024.
Full textAbstract:
A constitutive model based on rate-independent elastoplasticity concepts is developed and used to simulate the behavior of geologic materials under arbitrary three-dimensional stress paths. The model accounts for various factors such as friction, stress path and stress history that influence the behavior of geologic materials. A hierarchical approach is adopted whereby models of progressively increasing sophistication are developed from a basic isotropic-hardening associative model. Nonassociativeness is introduced as correction or perturbation to the basic model. Deviation of normality of the plastic strain increments to the yield surface F is captured through nonassociativeness. The plastic potential Q is obtained by applying a correction to F. This simplified approach restricts the number of extra parameters required to define the plastic potential Q. The material constants associated with the model are identified, and they are evaluated for three different sands (Leighton Buzzard, Munich and McCormick Ranch). The model is then verified by comparing predictions with laboratory tests from which the constants were found, and typical tests not used for finding the constants. The effect of varying initial density of a material on the stress-strain and volumetric response is investigated. An empirical relation is proposed, whereby one parameter is modified based on the initial density, such that improved predictions can be obtained without increasing the total number of parameters. Implementation of the nonassociative model in a finite element program to solve boundary value problems leads to a nonsymmetric stiffness matrix. Besides, using a nonsymmetric solver, three numerical schemes are investigated. The idea of the schemes is to modify the stiffness matrix such that a symmetric equation solver can be used. Prediction of stress-strain, volumetric response and CPU time for different schemes are compared with the predictions obtained using the nonsymmetric solver. The nonsymmetric equation solver used less CPU time and the solutions were more accurate. Based on the above findings, a soil-footing system is analyzed using the finite element techniques. The associative and nonassociative models are used to predict the behavior. For the nonassociative model, solution is obtained by using a nonsymmetric solver. Results obtained from both models are compared with a model footing test performed in the laboratory.
49
GALAGODA, HERATH MAHINDA. "NONLINEAR ANALYSIS OF POROUS SOIL MEDIA AND APPLICATION (PORE PRESSURE, TIME INTEGRATION, FINITE ELEMENTS)." Diss., The University of Arizona, 1986. http://hdl.handle.net/10150/183913.
Full textAbstract:
The behavior of porous media subjected to any arbitrary loading is a complex phenomenon due to the coupled nature of the problem. Proper understanding of this coupled behavior is essential in dealing with many of the geotechnical engineering problems. A very general three-dimensional formulation of such a coupled problem was first reported by Biot; however, a two-dimensional idealization of the theory is used here with extension to nonlinear material behavior. A finite element computer code is developed to analyze the response of coupled systems subjected to both static and dynamic excitations. The code can also be used to solve problems involving only solid media by suppressing the presence of fluid. The generalized anisotropic hardening model is implemented into the finite element procedure to characterize nonlinear material behavior throughout the realm of its deformation process. Both drained and undrained conditions are considered in order to verify the performance of the model in capturing material behavior. Three different materials are considered for this purpose. The predictions obtained using the anisotropic model for both drained and undrained condition yield satisfactory comparison with observed behavior. The finite element procedure is verified by solving several problems involving undrained, consolidation and dynamic responses of coupled system. Good agreements are found between numerical and analytical results. Further verification of the computer code and the material model is performed by solving two boundary value problems. For this purpose, a laboratory pressuremeter test subjected to quasi-static loading condition and a building foundation system subjected to rapid earthquake excitation were analyzed. The results of this research have provided an improved understanding of coupled behavior of porous media. The procedure developed here can be effectively used under a wide range of loading conditions varying from very slow quasi-static to very rapid earthquake excitations.
50
Kokorev, A. E., A. O. Kiriak, and О. Г. Аврунін. "Some Models of Mechanical and Thermal Properties of Skin in the Context of Plastic Surgery." Thesis, Kharkiv, KNURE, 2019. http://openarchive.nure.ua/handle/document/10196.
Full text