To see the other types of publications on this topic, follow the link: Constitutive Model.
Dissertations / Theses on the topic 'Constitutive Model'
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 'Constitutive Model.'
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
Adi, Riyono Winarputro. "CJS-RE : a hierarchical constitutive model for rammed earth." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEC036/document.
Full textAbstract:
Le pisé est une technique constructive vernaculaire consistant à compacter successivement des couches de terre humide entre des coffrages. Cette technique, présente dans le monde entier, l'est en particulier en France dans la région Auvergne-Rhône-Alpes. Comme il n'existe pas de réglementation attachée à cette technique constructive, il est très difficile pour des propriétaires de réparer leur bien. Le développement de cette technique pour de nouveaux projets souffre aussi de cette absence alors qu'elle répond à certains enjeux posés par le Développement Durable. Le travail présenté ici fait partie intégrante du projet national PRIMATERRE dédié à l'étude des constructions impliquant de la terre. Une loi de comportement élasto-plastique est développée dans ce travail pour modéliser le comportement du pisé. Elle s'appuie sur une approche hiérarchisée de la modélisation en lien avec le nombre d'essais disponibles pour identifier les paramètres de modèle mais aussi en lien avec la complexité de phénomènes à prendre en compte. Ce modèle s'inspire d'un modèle pré-existant, CJS, développé en géotechnique pour modéliser le comportement mécanique des matériaux granulaires. Une adaptation s'est imposée pour prendre en compte les spécificités du comportement mécanique du pisé qui possède de nombreuses similitudes avec celui des matériaux quasi-fragiles. Deux niveaux de modélisation pour le modèle de comportement appelé CJS-RE sont présentés, pouvant être utilisés dans un contexte de sollicitation monotone. Le premier niveau CJS-RE1 est un modèle élastique parfaitement plastique alors que le second niveau CJS-RE2 est un modèle élasto-plastique à écrouissage isotrope. Deux mécanismes de déformation plastique sont présents, l'un lié aux phénomènes purement déviatoires et l'autre aux phénomènes de traction. La validation du modèle a été entreprise sur la base de la simulation d'essais en laboratoire de compression diagonale et de chargement latéral (pushover) sur des murets, issus de la littérature. Le niveau CJS-RE1 a été capable de capturer les phénomènes essentiels issus de ces deux tests et peut être utilisé comme une première approches des problèmes. Le niveau CJS-RE2 a permis de retrouver plus précisément le comportement non linéaire du pisé sur une large gamme de déformations, que ce soit dans l'essai de compression diagonale ou dans le pushover. Enfin, la prise en compte d'interfaces entre les couches dans la modélisation semble constituer une approche surdimensionnée lorsque seule la résistance d'un système constitué en pisé est recherchée. Cependant, parce qu'elles apportent une certaine ductilité au système dans la modélisation, elles peuvent être utilisées lorsque des résultats plus détaillés sont attendus<br>Rammed earth is a vernacular building technique consisting in compacting successively layers of moist earth within formworks. This technique is present worldwide and in particular in the region Auvergne-Rhône-Alpes in France. As no regulation exists for rammed earth structures in France, the owners of such structures are helpless at the time when repairing damages appearing in any aging heritage structures. Moreover, this lack of regulation tends to slow down the development of such a constructive solution in new projects though this technique answers many of the issues raised by the sustainable development. The work presented herein is part of the national research project PRIMATERRE devoted to the study of construction building involving earth. Herein, an elasto-plastic constitutive law is developed for modeling the behavior of rammed earth. It is based on a hierarchical approach of the modeling in relation to the information available to identify the set of model parameters and the refinement of phenomena to be modelled. This model was adapted from a pre-existing CJS model used in advanced foundation engineering for the modelling of granular soils. The necessary adaptation of some mechanisms of the model in the context of rammed earth material which holds the characteristics of a quasi-brittle material is highlighted. Two levels for the model denoted CJS-RE which can be used in the context of monotonous loadings are presented herein. The first level is a simple elastic perfectly plastic model (CJS-RE1) and the second model is an elasto-plastic model with an isotropic hardening (CJS-RE2). Two mechanisms of plastic deformation are involved, one related to purely deviatoric phenomena and one related to tensile phenomena. The validation of the model was performed based on different sets of actual tests including diagonal compression tests and pushover tests on wallets. The simple elasto-plastic model CJS-RE1 was able to capture some basic features for these two tests and may be used for a first estimate of the system resistance. The more sophisticated model CJS-RE2 was found better to retrieve the nonlinear behavior of rammed earth over a larger range of deformations throughout both a diagonal compression test and a pushover test. Finally, the modelling of interfaces between layers of earth seems oversized when the resistance of the system is investigated. However, since they may influence the simulated ductility of the system, they may be used to model the behavior of rammed earth system more precisely
2
Kelln, Curtis Gerald. "An elastic-viscoplastic constitutive model for soil." Thesis, Queen's University Belfast, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.491999.
Full textAbstract:
The concepts of elasticity and viscoplasticity were used to develop an elastic-viscoplastic (EVP) constitutive model for soil. The mathematical description of viscoplastic straining includes a measure of both effective stress and the corresponding volumetric packing of the soil particles. The model is able capture the dependence of stress-strain relationships and undrained shear strength on strain rate, the development of irrecoverable plastic strains at constant stress, which is creep, and the relaxation of stresses at constant strain. A Newton-Raphson solution scheme with a stress point algorithm was used to implement the EVP soil model in a finite element program. The algorithms and assumptions required to implement the solution scheme are provided. Verification of the solution scheme is achieved by using it to analyze typical boundary value problems. A case history is developed for a geotextile reinforced highway embankment constructed on a soft estuarine deposit installed with prefabricated vertical drains. The EVP soil model was then used to simulate the measured deformation response. The numerical simulations closely matched the temporal changes in pore water pressures and surface settlement beneath the centerline and shoulder of the embankment. More importantly, the elastic-viscoplastic model simulated the pattern and the magnitudes of the lateral deformations beneath the toe of the embankment;... a notoriously difficult aspect of modelling the deformation response of soft soils. The simulations were achieved using a small set of material constants that can easily be obtained from standard laboratory tests. The research validates the use of the EVP model for problems involving heterogeneous soft soil deposits beneath loading from a geotechnical structure.
3
SIMOES, LEONARDO CRAVEIRO. "A CONSTITUTIVE MODEL FOR FIBER REINFORCED CONCRETE." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1998. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=1511@1.
Full textAbstract:
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR<br>Nos últimos 40 anos, tem-se observado um crescente
interesse por compósitos formados pela adição de fibras a
matrizes de concreto, os chamados concretos reforçados com
fibras. Esse interesse é justificado, sobretudo, pelo
significativo ganho em tenacidade que as fibras
proporcionam, atenuando as características frágeis do
concreto. De fato, em virtude do mecanismo de reforço
promovido pelas fibras, o concreto com fibras é capaz de
absorver muito mais energia de deformação até a ruptura,
apresentando, no regime pós-fissuração, um comportamento
muito mais suave que o concreto simples. Esse comportamento
é acompanhado por um processo de fissuração mais uniforme,
no qual observam-se fissuras mais finas e menos espaçadas.
Além disso, registram-se aumentos nos valores de
resistência do material e nos níveis de deformação que ele
atinge até seu completo esgotamento.
Tendo em vista os benefícios que as fibras aportam ao
desempenho do concreto, seu emprego seria recomendável a
estruturas em que a ductilidade é um dos parâmetros
principais de projeto, ou naquelas feitas com concretos de
alta resistência, uma vez que estes apresentam um
comportamento ainda mais frágil que os concretos de
resistência normal. Além disso, a utilização de fibras no
combate aos esforços de cisalhamento mostra-se extremamente
vantajosa e promissora.
Neste trabalho, apresenta-se um modelo constitutivo para
concreto reforçado com fibras baseado na formulação
hipoelástica de ELWI E MURRAY (1979), originalmente
proposta para concreto simples. As especificidades do
comportamento do concreto com fibras frente às mais
diversas solicitações, tais como, tração, compressão e
cisalhamento, são incorporadas ao modelo através de
relações tensão-deformação adequadas a esse material. Tais
relações provêm de estudos analíticos e experimentais sobre
o assunto, publicados na literatura técnica especializada.
O modelo assim obtido é implementado no programa FEPARCS
(ELWI E MURRAY, 1980), capaz de realizar análises númericas
não-lineares através do método dos elementos finitos. Por
fim, utiliza-se esse program para simular a resposta de uma
estrutura de concreto com fibras, cujo ensaio experimental
aparece minuciosamente descrito em (CRAIG, 1987). Os
resultados numéricos obtidos são comparados com os
experimentais correspondentes, em termos da curva carga
versus deslocamento, desenvolvimento e distribuição de
fissuras, progressão do escoamento da armadura longitudinal
(convencional) e modo de ruptura. Avalia-se, então, a
eficiência da implementação realizada na descrição do
comportamento de estruturas de concreto com fibras.<br>Along the past forty years, an increasing interest on
composite materials formed by the
addition of discrete fibers to a concrete matrix is being
observed. These composites are known
as fiber reinforced concretes. The interest on the use of
fibers as reinforcement is justified by
their significative contribution to concrete thoughness, as
they reduce the brittle characteristics
of that material. In fact, due to fiber reinforcement
mechanism, fiber reinforced concrete can
absorb much more strain energy until failure, in comparison
to ordinary concrete. The cracking
process seems to be more uniform, as the distance between
cracks are reduced. Besides that,
the material strength and the deformation levels at
cracking and rupture are greater, on the
case of fiber reinforced concrete.
The benefits that fibers bring to concrete behavior
indicate that they could be used as
complementary reinforcent for concrete structures when
ductility is a major design concern, or
when high strength concrete is employed, as this class of
material tends to be much more brittle
then normal strength concrete. Fibers are also effective as
shear reinforcement, and they could
even replace stirrups in this function.
In this work, a constituive model for fiber reinforced
concrete is presented. This model
is based on the formulation originally proposed by ELWI AND
MURRAY (1979) for the case of
ordinary concrete. The behavior characteristcs of fiber
reinforced concrete are incorporated as
adaquated uniaxial stress-strain relations in tension and
compression. The behavior under shear
stress is also considered. The model is then implemented in
the finite element program
FEPARCS (ELWI AND MURRAY, 1980). A numerical analysis on
the response of a fiber
reinforced concrete structure is conducted. Results
reported in technical literature (CRAIG,
1987) are compared to those obtained by the finite element
analysis. The efficiency of the
model is then verified.<br>En los últimos 40 anos, se ha observado un creciente
interés por compuestos formados por la adición de fibras a
matrizes de concreto, los llamados concretos reforzados con
fibras. Ese interés se debe a la significativa ganancia en
tenacidad que las fibras proporcionan, atenuando las
características frágiles del concreto. De hecho, en virtud
del mecanismo de refuerzo promovido por las fibras, el
concreto con fibras es capaz de absorver mucha más energía
de deformación hasta la ruptura, presentando, en el régimen
posfisuración, un comportamiento mucho más suave que el
concreto simple. Este comportamiento se ve acompañado por
un proceso de fisuración más uniforme, en el cual se
observan fisuras más finas y menos espaciadas. Además, se
registran aumentos en los valores de resistencia del
material y en los niveles de deformación que alcanza hasta
su completa destrucción. Teniedo en cuenta los beneficios
que las fibras aportan al desempeño del concreto, sería
recomendable su empleo en extructuras donde la ductilidad
es uno de los parámetros principales de proyecto, o en
aquellas hechas con concreto de alta resistencia, ya que
éstos presentan un comportamiento más frágil que los
concretos de resistencia normal. En este trabajo, se
presenta un modelo constitutivo para concreto reforzado con
fibras que tiene como base la formulación hipoelástica de
ELWI Y MURRAY (1979), originalmente propuesta para concreto
simple. Las especificidades del comportamiento del concreto
con fibras frente a las más diversas solicitudes, tales
como, tracción, compresión y cisallamiento, se incorporan
al modelo a través de relaciones tensión-deformación
adecuadas a ese material. Tales relaciones provienen de
estudios analíticos y experimentales sobre el asunto,
publicados en la literatura técnica especializada. La
implementación del modelo obtenido fue realizada a través
del programa FEPARCS (ELWI Y MURRAY, 1980), capaz de
realizar análisis númerico no lineal a través del método de
los elementos finitos. Por fin, se utiliza ese programa
para simular la respuesta de una extructura de concreto con
fibras, cuyo ensayo experimental aparece minuciosamente
descrito en (CRAIG, 1987). Los resultados numéricos
obtenidos se comparan con los experimentales
correspondientes, considerando la curva carga versus
deslocamiento, desarrollo y distribuición de fisuras,
progresión del deslizamiento de la armadura longitudinal
(convencional) y modo de ruptura. Se evalúa entonces, la
eficiencia de la implementación en la descrición del
comportamiento de extructuras de concreto con fibras.
4
Kim, Se-Hyung. "Cyclic Uniaxial Constitutive Model For Steel Reinforcement." Thesis, Virginia Tech, 2015. http://hdl.handle.net/10919/51241.
Full textAbstract:
Reinforced Concrete (RC) structures are common in earthquake-prone areas. During an
earthquake, the steel reinforcement is subjected to cyclic strain histories which lead to inelastic response. In the case of rare, strong earthquakes, inelastic buckling and even rupture due to low-cycle fatigue can also occur. The understanding and characterization of the performance of RC structures under earthquake hazards requires the accurate simulation of the inelastic hysteretic behavior of steel reinforcement by means of appropriate constitutive models.
Several uniaxial material models have been developed for reinforcing steel. Existing
material models sacrifice efficiency for accuracy or vice versa. Conceptually simple and
numerically efficient models do not accurately capture the hysteretic response and ignore rupture or buckling. On the other hand, more refined material models are characterized by iterative stress update procedures which can significantly increase the computational cost of an analysis. Additionally, experience suggests that refined models attempting for the effect of inelastic
buckling tend to lead to numerical convergence problems in the stress update procedure.
The goal of the present study is the formulation and implementation of an accurate and
computationally efficient constitutive model for steel reinforcement under cyclic loading. A
previously developed model, capable of capturing the inelastic hysteretic response of reinforcing steel in the absence of buckling and rupture, is used as a starting point in this study. The model is enhanced by replacing its original, iterative stress update procedure with an equally accurate, non-iterative one. Additionally, the model is enhanced to capture the effects of inelastic buckling and of rupture. The accuracy of the model and the efficiency of the non-iterative stress update algorithm are demonstrated by means of validation analyses.<br>Master of Science
5
Babbepalli, Venkata Venu Sai Phani Ram. "Implementation of moisturedependent constitutive model for paperboard." Thesis, KTH, Hållfasthetslära, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-284356.
Full textAbstract:
There has been a considerable increase in the usage of paper products due to its sustainability in the product cycle. Many environmental and process variables can affect the mechanical behavior of paper from its making to finished products. Of these variables, moisture is of particular importance and strongly influences both papermaking, converting, and end-use of the paper products. Experimental investigations at different humidity levels reveals that normalized in-plane constitutive parameters, such as elastic parameters and the linear hardening modulus, in both MD and CD1) follow a linear relationship with normalized moisture ratio. This relation is found to be acceptable for a wide range of commercial paperboards. To capture this observation, a novel material model with orthotropic elasticity and anisotropic hardening2 is proposed. An associative flow rule for the evolution of plastic strain is proposed. The proposed flow rule is such that all stresses contribute to plastic flow rather than an effective stress. A simple version using anisotropic linear hardening is implemented. The mechanical properties, such as elastic parameters and hardening moduli are considered functions of the moisture ratio. An implicit variant of the material model is implemented in LS-DYNA®. The simulations with the proposed material model at different humidity levels follow the experimental results well for uniaxial loading, but discrepancies are obtained for simulation of biaxial loading tests. The moisture is assumed constant in the proposed model since the experiments are done in a moisture-controlled environment.<br>Användningen av pappersprodukter har ökat avsevärt på grund av dess hållbarhet i produktcykeln. Många miljö- och processvariabler kan påverka papperets egenskaper från tillverkning till färdig produkt. Av dessa variabler är fukt särskilt viktig och fukt påverkar kraftigt både tillverkning, konvertering och slutanvändning av pappersprodukter. En experimentell undersökning vid olika fuktighetsnivåer visar att normaliserade konstitutiva parametrar, såsom elastiska styvheter och tangentmodulen i papperets plan i både MD och CD, uppvisar ett linjärt samband som funktion av normaliserad fuktkvot. Detta samband har visat sig vara en god approximation för ett stort antal kommersiella kartonger. En ny materialmodell baserad på ortotrop elasticitet och anisotropt hårdnande föreslås med hänsyn till detta. En associativ flytlag för plastisk deformation föreslås. Den föreslagna flytlagen är sådan att alla spänningar bidrar till den plastiska deformationen snarare än effektivspänningen. En enklare version baserad på linjärt anisotropt hårdnande har modellerats. De mekaniska egenskaperna såsom styvhet och hårdnandemodul anses vara funktioner av fuktkvoten och följa de linjära sambanden. En implicit variant av materialmodellen är implementerad i LS-DYNA®. Simuleringar med den föreslagna materialmodellen vid olika fuktkvoter följer de experimentella resultaten väl vid enaxlig belastning medan vissa avvikelser uppträder vid tvåaxlig belastning. I den föreslagna modellen antas fukten antas vara konstant eftersom de bakomliggande experimenten genomfördes i en fuktkontrollerad miljö.
6
Chen, Cheng-Wei. "A constitutive model for fiber-reinforced soils." Diss., Columbia, Mo. : University of Missouri-Columbia, 2007. http://hdl.handle.net/10355/4768.
Full textAbstract:
Thesis (Ph. D.)--University of Missouri-Columbia, 2007.<br>The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Typescript. Vita. Title from title screen of research.pdf file (viewed on March 6, 2009) Includes bibliographical references.
7
Mei, Zhu. "Structural hybrid simulation with model updating of material constitutive model." Doctoral thesis, Università degli studi di Trento, 2018. https://hdl.handle.net/11572/368550.
Full textAbstract:
When hybrid simulation (HS) with substructures is employed for assessing the seismic behavior of a large complex structure, it is unrealistic to test all the components that may exhibit strong nonlinearity. Hence, the accuracy of the numerical substructure (NS) faces an increased challenge. To this end, this paper will emphasize on improving the accuracy of the NS in hybrid simulation based on the model updating approach. Most hybrid simulations with model updating (UHS) focus on updating the parameters of the component constitutive model (story shear model) leading to large modeling errors and the unknown detail responses. Moreover, the most extensively used component constitutive models, such as the Bouc-Wen model, are the models in a narrow sense because they are different for various RC members when the size of the component, boundary conditions, axial compression ratio, and the volumetric stirrup ratio are different from one component to the other. Thus, numerous parameters are needed to describe the displacement-force relations of different components, which leads to the huge computational burden. With this respect, this paper proposes a novel hybrid simulation approach based on identifying and updating the parameters of the material constitutive model. The main work and results are concluded as follows,
1. The unified constitutive model of unconfined and confined concrete is derived from the existing uniaxial concrete constitutive models by introducing the volumetric stirrup ratio.
2. To solve the problem that the relation of the measurements (force of the specimen of a RC member) and the identified parameters (concrete constitutive parameters) are difficult to analytical expressed, an OpenSees embedded unscented Kalman filter is proposed for parameter identification. To this end, several parts of the OpenSees source codes are developed and modified.
3. The proposed identification method and hybrid simulation based on updating the concrete constitutive parameters are respectively validated through a monotonic loading test on a RC column and a UHS on a RC frame. The results show that the convergence values of each parameter under various experimental cases are close to each other with a small variance, which indicates that the proposed identification method is robust and reliable. Comparing to the standard HS, the accuracy of the NS, hence the UHS, is significantly improved.
4. Apply the proposed UHS to a RC continuous rigid bridge with tall thin-walled piers. It concludes that the performance of the identification method is still quite good. Contrasting to the simpler structure, the improved accuracy of a large complex structure is even greater. Moreover, the accuracy of the NS can be greatly increased even though the model error is increased. By tuning the initial values of constitutive parameters, the negative influence of model error is decreased to further improve the precision of the NS. By observing the specimen, it is found that the thin-walled hollow section specimen is a bending-shear type damage mode and finally damaged due to the tensile rupture of the stirrup.
8
Mei, Zhu. "Structural hybrid simulation with model updating of material constitutive model." Doctoral thesis, University of Trento, 2018. http://eprints-phd.biblio.unitn.it/2959/1/TESI_ZHU_MEI.pdf.
Full textAbstract:
When hybrid simulation (HS) with substructures is employed for assessing the seismic behavior of a large complex structure, it is unrealistic to test all the components that may exhibit strong nonlinearity. Hence, the accuracy of the numerical substructure (NS) faces an increased challenge. To this end, this paper will emphasize on improving the accuracy of the NS in hybrid simulation based on the model updating approach. Most hybrid simulations with model updating (UHS) focus on updating the parameters of the component constitutive model (story shear model) leading to large modeling errors and the unknown detail responses. Moreover, the most extensively used component constitutive models, such as the Bouc-Wen model, are the models in a narrow sense because they are different for various RC members when the size of the component, boundary conditions, axial compression ratio, and the volumetric stirrup ratio are different from one component to the other. Thus, numerous parameters are needed to describe the displacement-force relations of different components, which leads to the huge computational burden. With this respect, this paper proposes a novel hybrid simulation approach based on identifying and updating the parameters of the material constitutive model. The main work and results are concluded as follows,
1. The unified constitutive model of unconfined and confined concrete is derived from the existing uniaxial concrete constitutive models by introducing the volumetric stirrup ratio.
2. To solve the problem that the relation of the measurements (force of the specimen of a RC member) and the identified parameters (concrete constitutive parameters) are difficult to analytical expressed, an OpenSees embedded unscented Kalman filter is proposed for parameter identification. To this end, several parts of the OpenSees source codes are developed and modified.
3. The proposed identification method and hybrid simulation based on updating the concrete constitutive parameters are respectively validated through a monotonic loading test on a RC column and a UHS on a RC frame. The results show that the convergence values of each parameter under various experimental cases are close to each other with a small variance, which indicates that the proposed identification method is robust and reliable. Comparing to the standard HS, the accuracy of the NS, hence the UHS, is significantly improved.
4. Apply the proposed UHS to a RC continuous rigid bridge with tall thin-walled piers. It concludes that the performance of the identification method is still quite good. Contrasting to the simpler structure, the improved accuracy of a large complex structure is even greater. Moreover, the accuracy of the NS can be greatly increased even though the model error is increased. By tuning the initial values of constitutive parameters, the negative influence of model error is decreased to further improve the precision of the NS. By observing the specimen, it is found that the thin-walled hollow section specimen is a bending-shear type damage mode and finally damaged due to the tensile rupture of the stirrup.
9
Junior, Wanderley Camargo Russo. "Desenvolvimento de um modelo hipoplástico que represente efeitos do sobreadensamento." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/3/3145/tde-19092006-170548/.
Full textAbstract:
São propostas modificações em um modelo hipoplástico buscando representar o comportamento mecânico de argilas sobreadensadas. São introduzidos no modelo a razão de sobreadensamento, o intercepto de coesão e índices que representam características do trecho sobreadensado, resultando em parâmetros com claro sentido físico e de fácil determinação. A equação constitutiva é então calibrada com parâmetros de solos sobreadensados e a capacidade dos modelos de representar o comportamento de dois solos em particular é verificada, confrontando as previsões teóricas com resultados experimentais em diversas situações de carregamento e para uma larga faixa de razões de sobreadensamento. Verifica-se que as modificações introduzidas no modelo hipoplástico contemplam avanços significativos na representação dos efeitos do sobreadensamento, como a curvatura da envoltória de resistência no trecho sobreadensado, o aumento do módulo de deformabilidade com o grau de sobreadensamento, diferente rigidez no carregamento e no recarregamento, o aumento das tensões desviadoras de ruptura em solos sobreadensados, a diminuição da tendência à contração volumétrica com o aumento da razão de sobreadensamento, chegando à expansão volumétrica, e, nas solicitações não-drenadas, pressão neutra negativa quando o solo encontra-se fortemente sobreadensado.<br>Modifications in a hypoplastic model are proposed intending to represent the mechanical behavior of overconsolidated clays. The overconsolidation ratio, the cohesion intercept and indices that represent overconsolidation characteristics are introduced in the model, resulting in parameters with a clear physical meaning and of easy to determine. The constitutive equation is then calibrated with parameters of overconsolidated soils and the capacity of the models of representing the behavior of two soils in particular is checked, confronting the theoretical predictions with experimental results in several loading situations and in a wide overconsolidation ratio range. It is verified that the modifications introduced into hypoplastic model contemplates significant advances in the representation of the effects of overconsolidation, like the curvature of the strength envelope in the overconsolidation region, the increase of the deformability modulus with the overconsolitadion ratio, different stiffness in loading and reloading, the increase of the deviator stress at failure in overconsolidated soils, presenting peak deviator stress, a decrease of the tendency to volumetric contraction with the increase of the overconsolidation ratio, including to the volumetric expansion, and, in undrained tests, negative pore pressure when the soil is heavily overconsolidated.
10
Pisoni, Attilio C. (Attilio Carlo). "A constitutive model for friction in metal-working." Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/12620.
Full text
11
Su, Cheng Ph D. Massachusetts Institute of Technology. "A continuum constitutive model for amorphous metallic materials." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/38928.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.<br>Includes bibliographical references (leaves 153-161).<br>A finite-deformation, Coulomb-Mohr type constitutive theory for the elastic-viscoplastic response of pressure-sensitive and plastically-dilatant isotropic materials has been developed. The constitutive model has been implemented in a finite element program, and the numerical capability is used to study the deformation response of amorphous nietallic glasses. Specifically, the response of an amorphous metallic glass in tension, compression, strip-bending, and indentation is studied, and it is shown that results from the numerical simulations qualitatively capture major features of corresponding results from physical experiments available in the literature. The response of a Zr-based glass in instrumented plane strain indentation with a cylindrical indenter tip is also studied experimentally. The constitutive model and simulation capability is used to numerically calculate the indentation load versus depth curves, and the evolution of corresponding shear-band patterns under the in-denter. The numerical simulations are shown to compare very favorably with the corresponding experimental results. The constitutive model is subsequently extended to the high homologous temperature regime, and the response of a representative Pd-based metallic glass in tension at various strain rates and temperatures with different pre-annealing histories is studied.<br>(cont.) The model is shown to capture the major features of the stress-strain response and free volume evolution of this metallic glass. In particular, the phenomena of stress overshoot and strain softening in monotonic experiments at a given strain rate and temperature, as well as strain rate history effects in experiments involving strain rate increments and decrements are shown to be nicely reproduced by the model. Finally, a cavitation mechanism is incorporated in the constitutive model to simulate the failure phenomenon caused by the principal and hydro-static stresses. With the revised theory, the response of a prototypical amorphous grain-boundary is investigated, and the result is later applied to study the deformation and failure behavior of nanocrystalline fcc metals by coupling with appropriate crystal-plasticity constitutive model to represent the grain interior.<br>by Cheng Su.<br>Ph.D.
12
Pestana-Nascimento, Juan Manuel. "A unified constitutive model for clays and sands." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/11724.
Full text
13
Reed, Philip Edward 1959. "A variable moduli probabilistic constitutive model for soils." Thesis, The University of Arizona, 1988. http://hdl.handle.net/10150/276754.
Full textAbstract:
Measurement of stress - strain relationships in soil systems usually incorporate varying degrees of uncertainty. These uncertainties arise from laboratory testing mechanisms, sampling disturbances, errors performed by operators or technicians performing the tests, etc. Currently, deformation analyses have been modeled using several deterministic techniques. However, because of the uncertainties involved, there is a need to adapt these numerical methods into probabilistic models. This thesis develops a probabilistic constitutive model based on a variable moduli deterministic technique. First-order, second-moment stochastic methods are used to estimate a mean stress - strain curve and its ±1 standard deviation from raw data obtained on nearly identical, remolded sand samples. Probabilistic estimations for Bulk and Shear moduli are determined from the estimated mean curves and are used to develop a probabilistic constitutive model. Through the use of a probabilistic constitutive matrix, a stochastic equation is produced which can relate strains to any stress state imposed on a particular soil. This is verified through an example.
14
James, Christopher James. "AN ANISOTROPIC CONSTITUTIVE MODEL FOR NUCLEAR GRADE GRAPHITE." Cleveland State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=csu1544027689571583.
Full text
15
Shafieian, Mehdi. "Toward a Universal Constitutive Model for Brain Tissue." Diss., Temple University Libraries, 2012. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/204511.
Full textAbstract:
Mechanical Engineering<br>Ph.D.<br>Several efforts have been made in the past half century to characterize the behavior of brain tissue under different modes of loading and deformation rates; however each developed model has been associated with limitations. This dissertation aims at addressing the non-linear and rate dependent behavior of brain tissue specially in high strain rates (above 100 s-1) that represents the loading conditions occurring in blast induced neurotrauma (BINT) and development of a universal constitutive model for brain tissue that describes the tissue mechanical behavior from medium to high loading rates.. In order to evaluate the nature of nonlinearity of brain tissue, bovine brain samples (n=30) were tested under shear stress-relaxation loading with medium strain rate of 10 s-1 at strain levels ranging from 2% to 40% and the isochronous stress strain curves at 0,1 s and 10 s after the peak force formed. This approach enabled verification of the applicability of the quasilinear viscoelastic (QLV) theory to brain tissue and derivation of its elastic function based on the physics of the material rather than relying solely on curve fitting. The results confirmed that the QLV theory is an acceptable approximation for engineering shear strain levels below 40% that is beyond the level of axonal injury and the shape of the instantaneous elastic response was determined to be a 5th order odd polynomial with instantaneous linear shear modulus of 3.48±0.18 kPa. To investigate the rate dependent behavior of brain tissue at high strain rates, a novel experimental setup was developed and bovine brain samples (n=25) were tested at strain rates of 90, 120, 500, 600 and 800 s-1 and the resulting deformation and shear force were recorded. The stress-strain relationships showed significant rate dependency at high rates and was characterized using a QLV model with a 739 s-1 decay rate and validated with finite element analysis. The results showed the brain instantaneous elastic response can be modeled with a 3rd order odd polynomial and the instantaneous linear shear modulus was 19.2±1.1 kPa. A universal constitutive model was developed by combining the models developed for medium and high rate deformations and based on the QLV theory, in which the relaxation function has 5 time constants for 5 orders of magnitude in time (from 1 ms to 10 s) and therefore, is capable of predicting the brain tissue behavior in a wide range of deformation rates. Although the universal model presented in this study was developed based on only shear tests and the material parameters could not be found uniquely, by comparing the results of this study with previously available data in the literature under tension unique material parameters were determined for a 5 parameter generalized Rivlin elastic function (C10=3.208±0.602 kPa, C01=4.191±1.074 kPa, C11=79.898±18.974 kPa, C20=-37.093±7.273 kPa, C02=-37.712±5.678 kPa). The universal constitutive model for brain tissue presented in this dissertation is capable of characterizing the brain tissue behavior under large deformation in a wide range of strain rates and can be used in computational modeling of Traumatic Brain Injury (TBI) to predict injuries that result from falls and sports to automotive accidents and BINT.<br>Temple University--Theses
16
Liu, Rui. "A unified constitutive material model with application to machining." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/53097.
Full textAbstract:
Finite element simulation of metal cutting processes offers a cost-effective method to optimize the cutting conditions and to select the right tool material and geometry. A key input to such simulations is a constitutive model that describes material behavior during severe plastic deformation. However, the vast majority of material models used in prior work are phenomenological in nature and are usually obtained by fitting a non-physically based mathematical equation to the macro-scale stress-strain response of the material. Moreover, the deformation range covered by the stress-strain response used in the model calibration process usually falls short of the ranges typically observed in metal cutting.
This thesis seeks to develop a unified material model that explicitly incorporates microstructure evolution into the constitutive law to describe the macro-scale plastic deformation response of the material valid over the range of strains, strain rates and temperatures experienced in machining. The proposed unified model is based on the underlying physics of interactions of mobile dislocations with different short and long range barriers and accounts for various physical mechanisms such as dynamic recovery and dynamic recrystallization. In addition, the inclusion of microstructure evolution into the constitutive model enables the prediction of microstructure in the chip and the machined surface. In this study, the unified material model is calibrated and validated in the severe plastic deformation regime characteristic of metal machining and is then implemented in finite element simulations to evaluate its ability to predict continuous and segmented chip formation in machining of pure metals such as OHFC copper and commercially-pure titanium (CP-Ti).
Due to the physical basis of the proposed unified material model, the continuous chip formation observed in orthogonal cutting of OFHC copper is shown to be successfully predicted by the finite element model utilizing a version of the unified material model that explicitly accounts for microstructure evolution as well as dislocation drag as a plausible deformation mechanism applicable at the high strain rates common in metal cutting operations. The segmented or shear localized chip formation in orthogonal cutting of CP-Ti is also shown to be successfully simulated by the unified model after incorporating the inverse Hall-Petch effect arising from the ultrafine grain structure within the shear band. For both metals, the model is experimentally validated using flow stress data as well as machining data including cutting and thrust forces and relevant chip morphology parameters. Machining simulations carried out using the unified material model also yield useful insights into the microstructure evolution during the machining process, which is shown to be consistent with the available experimental data and the known physical understanding of severe plastic deformation behavior of the metals.
17
Laranjeira, de Oliveira Filipe. "Design-oriented constitutive model for steel fiber reinforced concrete." Doctoral thesis, Universitat Politècnica de Catalunya, 2010. http://hdl.handle.net/10803/6174.
Full textAbstract:
En los últimos años la industria viene exigiendo el empleo del hormigón reforzado con fibras de acero (HRFA) en aplicaciones estructurales. Debido al hecho de que la resistencia pos-fisuración del material es relevante, la capacidad de coser fisuras concedida por las fibras puede permitir la sustitución, parcial o total, de la armadura de acero convencional. Por consiguiente, una adecuada caracterización del comportamiento a tracción uniaxial del HRFA es de gran interés. Sin embargo, a pesar de la amplitud de trabajo de investigación y de la reciente elaboración de normativas, no existe un consenso respecto al modelo constitutivo a ser empleado en el diseño del HRFA.<br/><br/>El cosido de las fibras de acero en las fisuras mejora la tenacidad y la durabilidad del hormigón. El HRFA es un material que, generalmente, presenta una resistencia residual a tracción en régimen fisurado. Sin embargo, en algunas situaciones, el HRFA puede desarrollar endurecimiento en flexotracción debido a su aptitud en redistribuir esfuerzos en la sección de fisura. Estas características vienen contribuyendo para un interés creciente así como un incremento del número de aplicaciones de este material.<br/><br/>En esta tesis doctoral se desarrolla un método directo y lógico para predecir la respuesta a tracción del HRFA para el diseño estructural. Mientras que la comprensión del comportamiento del material se consigue por medio de una investigación experimental, la formulación del nuevo modelo constitutivo se obtiene con un estudio segmentado del comportamiento del material en niveles de menor complejidad y, en seguida, con la caracterización de cada uno de ellos hasta conseguir explicar la respuesta a tracción del HRFA.<br/><br/>Esta tesis está dividida en cinco partes principales: I) Identificación de las motivaciones. II) Obtención de resultados a tracción uniaxial para comprender los principales mecanismos que controlan la resistencia pos-fisuración. III) Desarrollo de dos modelos para predecir la respuesta al arrancamiento de fibras de acero inclinadas, que cubren fibras rectas y con ganchos. IV) Investigación detallada de la orientación de las fibras al nivel individual mediante análisis estadísticos. Luego, aspectos prácticos asociados al proceso de producción son integrados en una metodología innovadora para predecir la orientación de las fibras. V) Formulación y validación del nuevo modelo constitutivo, con base en las Partes III y IV, con los resultados experimentales de la Parte II. El comportamiento a tracción se evalúa mediante un estudio paramétrico y se proponen expresiones ingenieriles para el diseño y optimización (EEDO).<br/>El modelo constitutivo propuesto se distingue de estudios anteriores en varios aspectos y define una nueva filosofía para el diseño de elementos de HRFA. Este modelo es un método directo y práctico para obtener el comportamiento a tracción del material mediante parámetros con sentido físico y basado en conceptos claros: arrancamiento y orientación de las fibras.<br/><br/>Una de las principales aportaciones de este trabajo es la capacidad de predecir curvas tensión-apertura de fisura que reflejan una combinación específica de las propiedades de la matriz y de las fibras empleadas. Además, se introduce una filosofía innovadora en el diseño debido a la incorporación del proceso de producción, las propiedades en estado fresco y el elemento a construir en la definición del diagrama constitutivo.<br>In the last years, the industry has been demanding for the use of steel fiber reinforced concrete (SFRC) in structural applications. Because the post-cracking strength of this material is not negligible, the crack-bridging capacity provided by fibers may replace, partial or completely, conventional steel reinforcement. Therefore, an appropriate characterization of the SFRC uniaxial tensile behavior is of paramount interest. However, in spite of the extensive research and standards recently advanced, there is no agreement on the constitutive model to be used for the design of SFRC.<br/><br/>The crack-bridging capacity provided by steel fibers improves both the toughness and the durability of concrete. Conventional SFRC is a material which presents softening response under uniaxial tension, but may develop hardening behavior in bending due to its ability to redistribute stresses within the crosssection.<br/>These evidences have been contributing to an increasing interest and growing number of applications of this material.<br/><br/>In this doctoral thesis, a direct and rationale approach to predict the tensile response of SFRC for structural design calculations is developed. While insight on the material behavior is firstly gained through an experimental investigation, the formulation of the new constitutive model follows a bottomup approach: it fragments the material's behavior into levels of smaller complexity and then models each of them until the overall behavior can be explained.<br/><br/>The dissertation is subdivided into five main parts: I) The motivations for this research project are pointed out. II) Uniaxial tensile test results are obtained to understand the major mechanisms governing the post-cracking strength. III) Two models predicting the pullout responses of inclined steel fibers are developed, covering straight and hooked fibers. IV) The orientation of fibers is investigated in detail at the single fiber level through statistical analyses. Then, practical aspects associated to the manufacturing process are integrated within a novel framework to predict fiber orientation. V) Based on Parts III-IV, the new constitutive model is formulated and validated with experimental results from Part II. Further insight on the tensile behavior is gained through a parametric study and Engineered Expressions for Design and Optimization (EEDO) are proposed.<br/><br/>The proposed design-oriented constitutive model differentiates itself from previous studies in multiple aspects and defines a new philosophy for the design of SFRC elements. This model provides a direct and practical procedure to obtain the material's tensile behavior by means of parameters with physical meaning and based on clear concepts: fiber pullouts and orientations.<br/>One of the major contributions of this work is the ability to predict the stress-crack width curves that reflect the specific combination of the properties of the matrix and fibers applied. Furthermore, it introduces a novel philosophy for the material design regarding that the influences of the production process, fresh-state properties and the element to be built are taken into account to define the constitutive diagram.
18
Kiefer, Bjoern. "A phenomenological constitutive model for magnetic shape memory alloys." Texas A&M University, 2006. http://hdl.handle.net/1969.1/4712.
Full textAbstract:
A thermodynamics-based constitutive model is derived which predicts the nonlinear
strain and magnetization response that magnetic shape memory alloys (MSMAs) exhibit
when subjected to mechanical and magnetic loads. The model development
is conducted on the basis of an extended thermo-magneto-mechanical framework.
A novel free energy function for MSMAs is proposed, from which the constitutive
equations are derived in a thermodynamically-consistent manner. The nonlinear and
hysteretic nature of the macroscopic material behavior is captured through the evolution
of internal state variables which are motivated by the crystallographic and
magnetic microstructures of MSMAs. Model predictions are presented for different
relevant loading cases and analyzed in detail. Finally, magnetostatic boundary
value problems for MSMAs are considered and numerically solved using the finite
element method. For these computations the developed constitutive model provides
the nonlinear magnetic properties of the MSMA. The knowledge of the magnetic field
distribution in the computational domain as a function of the applied field, which
results from this magnetostatic analysis, is useful for the proper interpretation of
experimental results as well as the design of experiments and applications.
19
Mandel, Ulrich [Verfasser]. "Mechanism Based Constitutive Model for Composite Laminates / Ulrich Mandel." München : Verlag Dr. Hut, 2018. http://d-nb.info/1153254220/34.
Full text
20
Qiu, Yi. "An investigation into the microplane constitutive model for concrete." Thesis, University of Sheffield, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.311813.
Full text
21
GONDHALEKAR, ROHIT H. "A CONSTITUTIVE MODEL FOR NANOSTRUCTURES BASED ON SPATIAL SECANT." University of Cincinnati / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1120144896.
Full text
22
Romero, Ricardo J. "Development of a constitutive model for fiber-reinforced soils /." free to MU campus, to others for purchase, 2003. http://wwwlib.umi.com/cr/mo/fullcit?p3115585.
Full text
23
Tenev, Tichomir G. "An Elastic Constitutive Model of Spacetime and Its Applications." Thesis, Mississippi State University, 2019. http://pqdtopen.proquest.com/#viewpdf?dispub=10978458.
Full textAbstract:
<p> We introduce an elastic constitutive model of gravity that enables the interpretation of cosmological observations in terms of established ideas from Solid Mechanics and multi-scale modeling. The behavior of physical space is identified with that of a material-like medium called "cosmic fabric," which exhibits constitutive behavior. This cosmic fabric is a solid hyperplate that is broad in the three ordinary spatial dimensions and thin in a fourth hyperspatial dimension. Matter in space is treated as fabric inclusions that prescribe in-plane (three-dimensional) strain causing the transverse bending of the fabric into the fourth hyperspatial dimension. The linearized Einstein-Hilbert action, which governs the dynamics of physical space, is derived from postulating Hooke's Law for the fabric, and the Schwarzschild metric is recovered from investigating matter-fabric interactions. At the continuum length scale, the Principle of Relativity is shown to apply for both moving and stationary observers alike, so that the fabric's rest reference frame remains observationally indistinguishable at such a length scale. Within the Cosmic Fabric paradigm, the structural properties of space at different hierarchical length scales can be investigated using theoretical notions and computational tools from solid mechanics to address outstanding problems in cosmology and fundamental physics. For example, we propose and offer theoretical support for the "Inherent Structure Hypothesis", which states that the gravitational anomalies currently attributed to dark matter may in fact be manifestations of the inherent (undeformed) curvature of space. In addition, we develop a numerical framework wherein one can perform numerical "experiments" to investigate the implications of said hypothesis. </p><p>
24
Holmes, David William. "Aspects of finite strain constitutive model for semicrystalline polymers." Thesis, James Cook University, 2007. https://eprints.qut.edu.au/109545/1/HolmesPhDThesis.pdf.
Full textAbstract:
In this thesis, the development of a constitutive model for the finite strain deformation of semicrystalline polymers is presented. It reports on the formulation and numerical implementation of the model and the theoretical aspects of the associated experimental testing and parameter estimation.
Within both academia and industry to date, there exists no single constitutive model for semicrystalline polymers that is broadly accepted as representing the general case. This is in spite of the relatively complete scientific understanding of the material's response and the increasing use of such materials where structural loading can be significant. Numerical representation of such materials conventionally involves over-simplification of response, largely necessitated by the limitations of current experimental testing methods. A complex constitutive theory is only as powerful as the experimental method from which its parameters are fit. As such, the objective of this research was to develop a complete, generalized constitutive theory for semicrystalline polymers with a corresponding testing methodology that enables its practical use within industry.
The constitutive model selected can be characterized by a parallel combination of elastic, viscoelastic and viscoplastic model elements which most closely represents the complete deformation behavior of semicrystalline polymers in the pre-necking region (" < 15%). The accompanying mathematics are formulated for 3D, finite strain and are based on thermodynamic dissipation in keeping with conventional continuum mechanics methodology. Strain hardening has been found to be of importance within the viscoplastic element. The parallel configuration of the three model elements facilitates the decoupled algorithmic treatment of each response. This has been carried out in principal space, given the assumption of isotropy, making practical both its numerical implementation and the physical determination of model parameters. A strategy analogous to classical return mapping is used for solution of the viscoelastic evolution while a new, principal space, closest point projection return mapping algorithm has been developed for solution of the viscoplastic evolution, accounting for isotropic strain hardening. The consistent algorithmic tangential modulus is formulated to ensure quadratic convergence of the whole implicit finite element procedure.
The computational model has been verified through a series of simple finite element tests involving combinations of large strain normal and shear loadings, and large rigid body rotations. Several example problems have been solved as demonstration of the models versatility. Using the developed model, a study using numerical simulations of uniaxial and biaxial tensile testing methods has been carried out. Through this study it has been possible to develop an experimental methodology to isolate the component stress contributions from each of the three deforming modes as well as subset separation of viscous, yield, and isotropic hardening stresses for viscoplasticity. Via conventional optimisation procedures and an additionally developed iterative procedure for the viscoelastic response, this testing methodology makes possible the full specification of the model parameter set. Verification of the testing methodology was done via comparison between the calculated test curves, and values output directly from the numerical simulations.
The model proposed in this thesis corresponds to a general account of semicrystalline polymer constitutive response, possessing capabilities not accounted for previously in theories within the literature. Perhaps the most significant outcome from this work is the experimental data processing methodology that allows such a complex model to be accurately and practically fit to real materials. Being able to better predict the loaded response of semicrystalline polymers is critical for their continued and increased use in circumstances where structural loads are possible.
25
Tsoi, Wa Yeung. "Constitutive model development for lightly cemented scrap rubber tire chips /." View abstract or full-text, 2005. http://library.ust.hk/cgi/db/thesis.pl?CIVL%202005%20TSOI.
Full text
26
Wang, Shun-sheng. "Development of constitutive model for AL-2011 in mushy state." Ohio : Ohio University, 1994. http://www.ohiolink.edu/etd/view.cgi?ohiou1174224280.
Full text
27
Sun, Wenxian. "A dual constitutive communication-based model for managerial practice diffusion." Thesis, University of Hull, 2009. http://hydra.hull.ac.uk/resources/hull:2676.
Full textAbstract:
In the current research of managerial practice diffusion, discussions on how to understand and manage diffusion changes have been made primarily by drawing on institutional, rhetorical and systems theories for the reason that each of them seems to suggest a “mechanism” for diffusion. For instance, institutional theory suggests that diffusion is a changing process during which an organisation will continuously adapt itself to the outside environment in order to keep itself survival. Based on a rhetorical perspective, for which rhetoric plays an important role in diffusion, the achievement of a practice's diffusion/adoption relies on a three-period rhetorical justification which follows a Pathos-Logos-Ethos sequence. In the domain of systems theories, if diffusion is taken as a social system's reproduction, communication thus has a unique position in constituting such a system through autopoiesis (self-creation). Through comparing the above diffusion “mechanisms” suggested by different theories, it is found that some understandings for diffusion are shared in common. For example, a practice has to be legitimised in order to be diffused; communications for diffusions involve a process of filtering and creating meanings. Moreover, through analysing these “mechanisms”, the advantages and inadequacies of each can be recognised. Based on the analysis, the most outstanding issue identified is that for understanding and managing diffusion changes, a constitutive ontology that enables explorations on both people and diffusion circumstances (i.e. an organisation and its environment) is required. In this thesis, such an ontology is believed to be a social-constructionist-based one. A social-constructionist perspective assumes that the concepts of object and subject are connected in a “duality” rather than a “dualism”, and according to which, a practice is constituted during its diffusion, or in other words, it is constituted in people's action of teaching and learning this practice. Furthermore, such a constitutive process is accomplished in people's diffusion communications, which simultaneously construct a circumstance that either enables or constrains a diffusion change. In the discussion of how a constitutive communication works for diffusion, “communication duality” is defined in the sense that communication is a diffusion tool for justifying a practice which can be structured in a rhetorical way; it also selects and processes meanings of a practice relying on people's existing knowledgeabilities as a sensemaking-sensegiving (SM-SG) process. Consequently, an incorporated practice diffusion model based on a social-constructionist perspective is built which aims to suggest how a diffusion change can be enacted as well as how it can be analysed in practical terms. In the light of social constructionism, for which a researcher's ontology and epistemology jointly build each other, this thesis applies a self-ethnography strategy which follows a “SISI” (Survey-Immerse-Share-Integrate) methodology to analyse a real case of practice diffusion. The author's personal insights from this study suggest how a practice diffusion can be improved, as well as how a diffusion model can be enriched. In addition, the author's self-reflections on this research present how a communication research for practice diffusion could “constitute” a practice, and hence to help or inhibit its diffusion.
28
Nikolinakou, Maria-Aikaterini 1976. "A constitutive model for the compression behavior of Old Alluvium." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/44291.
Full textAbstract:
Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2008.<br>Includes bibliographical references.<br>Old Alluvium is classified as a transported, in-situ weathered tropical soil, and represents a class of geomaterials that have a complex microstructure, including cemented aggregates at the meso-scale and groups of clay stacks at the micro-scale. Despite the presence of significant fractions of nontronite (smectite species), the activity of charged clay particles is initially masked by the aggregation of iron oxides. Compression loading breaks the cementation at the meso-scale and causes physico-chemical changes at the micro-scale, which reveal the expansive characteristics of the clay minerals. It is difficult to achieve a fully disaggregated condition (through mechanical mixing or selective chemical dissolution) and hence, there is little practical value in referencing properties of the intact soil to a hypothetical disaggregated or intrinsic state as proposed for other bonded soils. The proposed formulation describes the variation of compressibility according to a measure of the microstructural changes using the Cation Exchange Capacity as a state variable. Upon load reversal, a model based on double layer theory is integrated to predict macroscopic volumetric expansion due to the swelling of the nontronitic clay fraction. This behavior is also linked to the Cation Exchange Capacity through the preconsolidation stress level, and hence, can accommodate changes in the clay swelling potential caused by mechanical or physicochemical loading. The model parameters depend on the compression characteristics of the intact soil, on measurements of the Cation Exchange Capacity in the intact and partially disaggregated states, on the amount of expandable minerals in the microstructure and on the initial hydration of the clay stacks.<br>(cont.) Overall, the proposed formulation introduces a new way of modeling the compression of bonded materials with evolving microstructural characteristics, which does not require a unique reference state. It builds the swelling response directly on the physicochemical characteristics of the soil. The thesis also includes an experimental program on block samples obtained from a tunneling project in San Juan, Puerto Rico. The laboratory data was used for the calibration and detailed validation of model predictions. The proposed formulation enables predictions of expected engineering properties through the vertical weathering profile of the Old Alluvium.<br>by Maria-Aikaterini Nikolinakou.<br>Sc.D.
29
Hickman, Randall John. "Formulation and Implementation of a Constitutive Model for Soft Rock." Diss., Virginia Tech, 2004. http://hdl.handle.net/10919/29000.
Full textAbstract:
Petroleum reservoirs located in the Norwegian sector of the North Sea have undergone unexpected subsidence of great magnitude (> 10 m) during more than 30 years of petroleum recovery operations. Historical laboratory investigations have shown that the subsidence is due to the mechanical behavior and mechanical properties of chalk. Chalk behavior is characterized by elastoplasticity, including pore collapse, shear failure, and tensile failure mechanisms; rate-dependence; and pore fluid dependence. The research described in this dissertation was performed with the objectives to formulate a constitutive model which describes all aspects of chalk and soft rock mechanical behavior, develop and/or implement methods to integrate the equations which form the constitutive model, and to apply the model to finite element simulations of engineering problems encountered in chalk and soft rock.
A new rate-dependent constitutive model is developed based on a three-dimensional extension of a volumetric time-lines model, similar to that of Bjerrum (1967). Shear and tensile failure surfaces are also included to reflect these failure mechanisms observed in chalk. Twelve model parameters are required to fully describe chalk behavior. Procedures to determine values for each of these parameters from laboratory test results are described. Correlations of model parameter values with index parameters are given for North Sea chalks, to allow reasonable values to be obtained in the absence of an extensive laboratory testing program. Comparisons between observed behavior and model simulations indicate that the new model is able to reproduce and predict the behavior of chalk quite well.
A new integration method for critical state cap plasticity models is presented. This new method may be used for rate-independent or rate-dependent constitutive models which are formulated with elliptical cap yield surfaces, including the chalk model. The new method gives results that compare favorably to integration methods used currently, in terms of accuracy and computational effort.
The effects of pore fluid composition on chalk behavior are included in the constitutive model. It is shown that the variability in constitutive behavior with pore fluid composition is due to dependence of model parameter values on pore fluid composition. This variability in model parameters with pore fluid composition has been quantified and implemented into the model for the complete spectrum of oil-water mixtures in chalk.
Finite element simulations are presented to demonstrate performance of the model in analyzing problems at several different scales, including laboratory, borehole, and full-field scales. A new algorithm called "equivalent uniform water saturation" has been developed to determine the average mechanical properties of finite chalk masses with non-uniform pore fluid compositions, which are frequently encountered during finite element simulations. Results of the laboratory-scale simulations indicate that the constitutive model can reproduce the inhomogeneous deformation patterns which occur in chalk during waterflooding tests, and that use of the new algorithm utilizing "equivalent uniform water saturation" produces consistent results for chalk masses with inhomogeneous pore fluid distributions when used with different finite element mesh discretizations. Results of the larger-scale simulations indicate that changes in pore fluid composition and pore fluid pressure have different effects on macro-scale chalk mechanical behavior, and that both must be considered during analysis.<br>Ph. D.
30
Kacker, Shubhra. "The Role of Constitutive Model in Traumatic Brain Injury Prediction." University of Cincinnati / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1563874757653453.
Full text
31
Saavedra, Flores Erick Isaac. "Computational multi-scale constitutive model for wood cell-wall mechanics." Thesis, Swansea University, 2011. https://cronfa.swan.ac.uk/Record/cronfa43160.
Full text
32
Zhang, Bo. "Constitutive modelling of municipal solid waste." Thesis, Loughborough University, 2007. https://dspace.lboro.ac.uk/2134/7984.
Full textAbstract:
Design of landfills must consider both stability and integrity of the lining system. Therefore, stresses and strains in both mineral and geosynthetic lining materials must be controlled. Interaction between waste and barrier system is of particular importance for assessing the stability and structural integrity of steep non-self supporting barrier systems. The most appropriate approach to assess the interaction is the use of numerical modelling techniques, and therefore an appropriate constitutive model for waste material is required to represent its mechanical behaviour. In a literature review the key aspects of mechanical behaviour of municipal solid waste (MSW) were investigated, including the influence of compressible and reinforcing particles on compression and shear behaviour of MSW were identified. Constitutive modelling of both MSW and soil material were reviewed, based on which the methodology for this study have been developed. In addition, requirements of an appropriate constitutive model for MSW have been suggested from the numerical modelling experience, and a framework to develop a constitutive model for MSW was produced. A one-dimensional compression model was developed by including the influence of compressible particles on MSW compression behaviour. One-dimensional compression tests on both real and synthetic waste samples were modelled and the results have shown that the compression model can reproduce the measured behaviour. A fibre reinforcing model was developed by including the influence of reinforcing particles on MSW shear behaviour. A triaxial compression test on fibre reinforced sand was modelled and the results have shown that the reinforcing model can predict its shear strength. A constitutive model for MSW has been developed by combining the Modified Cam-Clay with the one-dimensional compression and the fibre reinforcing models. Typical MSW triaxial compression tests have been modelled and the results have shown that the MSW model can reproduce the stress-strain behaviour in specific strain ranges. The constitutive model for MSW has been coded into a non-linear elasto-plastic finite element method program. Comparisons between the finite element analysis results and the analytical solutions have been performed and good agreements have been obtained.
33
Venkatasubramaniam, Shyam. "Constitutive Modeling of Poly(Ethylene Terephthalate)." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1417444300.
Full text
34
Phillips, Peter Louis. "Integrated Multiaxial Experimentation and Constitutive Modeling." University of Dayton / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1492598070791388.
Full text
35
García, Fernández Víctor Gerardo. "Constitutive relations to model the hot flow of commercial purity copper." Doctoral thesis, Universitat Politècnica de Catalunya, 2004. http://hdl.handle.net/10803/6043.
Full textAbstract:
Se ha llevado a cabo un estudio con el fin de observar diferencias en el comportamiento de fluencia en caliente de los cobres refinados al fuego con una pureza de 99.9%, dicho estudio ha permitido proponer modelos para predecir la curva esfuerzo-deformación y para predecir el tamaño de grano recristalizado dinámicamente. Los cobres refinados al fuego con una pureza de 99.9% se caracterizan por tener una composición residual de varios otros elementos, en algunos casos hasta 1000ppm. En los cobres con por lo menos 99.9% de pureza que tengan pocos elementos residuales, las diferencias observadas durante la fluencia en caliente se atribuyen a las interacciones entre átomos disueltos y dislocaciones, específicamente las interacciones con oxígeno intersticial. En el cobre electrolítico, el cual contiene principalmente altos contenidos de oxigeno, las diferencias de fluencia se atribuyen a cantidades cada vez mayores de partículas de Cu2O. Este trabajo más bien demuestra que las diferencias de esfuerzo encontradas en cobres refinados al fuego con una pureza de 99.9% son debidas a la cantidad de oxígeno residual, el cual forma finos precipitados a temperaturas intermedias que refuerzan la matriz metálica. A pesar del bajo contenido en oxígeno en los cobres estudiados (26-62ppm) se han caracterizado precipitados de Cu2O y se han utilizado teorías del endurecimiento por precipitación que han indicado que los precipitados de Cu2O eran los responsables del incremento en resistencia. Las interacciones entre átomos de oxígeno y dislocaciones son poco probables que causen un retro esfuerzo adicional a temperaturas superiores a los 600º C, en donde se ha llevado a cabo este trabajo. Se han comprimido tres cobres con 26, 46 y 62ppm de oxígeno a unas velocidades de deformación de 0.3s-1, 0.1s-1, 0.03s-1, 0.01s-1, 0.003s-1 y 0.001s-1 y a unas temperaturas desde 600º C hasta 950º C en intervalos de 50º. En este trabajo se presenta evidencia de cómo bajos contenidos de oxígeno en cobres 99.9% puros pueden afectar el comportamiento esfuerzo-deformación y el tamaño de grano recristalizado dinámicamente.<br/><br/>Además de haber encontrado el elemento y el mecanismo responsable del retro esfuerzo adicional también se presenta un algoritmo matemático para estudiar y predecir las oscilaciones de esfuerzo durante la recristalización dinámica de pico múltiple. Intentos anteriores utilizando Modelos Computarizados de Monte Carlo, Modelos de Autómatas Celulares o Modelos Matemáticos para la Recristalización Dinámica (DRX) no predicen las oscilaciones de esfuerzo de materiales reales y su tiempo de computo los hace inviables para procesos de simulación industrial. El nuevo Modelo de Avrami con Coseno Amortiguado para la DRX es capaz de predecir la transición de DRX de pico simple a DRX de pico múltiple. Además el nuevo modelo define el esfuerzo de estado estable sin tener que escoger un valor de una curva experimental que posiblemente no haya alcanzado un estado estable. Otra contribución del nuevo modelo es que demuestra que las oscilaciones son completamente predecibles en términos de la velocidad de deformación y la temperatura, una característica que antes se había dicho ser improbable. El nuevo modelo para la DRX junto con un modelo modificado de Voce-Kocks para la restauración dinámica han sido exitosamente implementados para predecir la fluencia en caliente.<br/><br/>Adicionalmente a las anteriores contribuciones este trabajo también da a conocer la relación que tiene el tamaño de grano recristalizado con la temperatura y la velocidad de deformación. Se asume que los cobres 99.9% puros, como los estudiados, tenderán a un tamaño de grano de estado estable el cual cuando esté a temperatura ambiente determinará las propiedades mecánicas del producto forjado.
36
Shepherd, James Ellison. "An internal state variable based constitutive model for semi-crystalline polymers." Thesis, Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/17638.
Full text
37
Stewart, Calvin. "A Hybrid Constitutive Model For Creep, Fatigue, And Creep-Fatigue Damage." Doctoral diss., University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/6023.
Full textAbstract:
In the combustion zone of industrial- and aero- gas turbines, thermomechanical fatigue (TMF) is the dominant damage mechanism. Thermomechanical fatigue is a coupling of independent creep, fatigue, and oxidation damage mechanisms that interact and accelerate microstructural degradation. A mixture of intergranular cracking due to creep, transgranular cracking due to fatigue, and surface embrittlement due to oxidation is often observed in gas turbine components removed from service. The current maintenance scheme for gas turbines is to remove components from service when any criteria (elongation, stress-rupture, crack length, etc.) exceed the designed maximum allowable. Experimental, theoretical, and numerical analyses are performed to determine the state of the component as it relates to each criterion (a time consuming process). While calculating these metrics individually has been successful in the past, a better approach would be to develop a unified mechanical modeling that incorporates the constitutive response, microstructural degradation, and rupture of the subject material via a damage variable used to predict the cumulative “damage state” within a component. This would allow for a priori predictions of microstructural degradation, crack propagation/arrest, and component-level lifing. In this study, a unified mechanical model for creep-fatigue (deformation, cracking, and rupture) is proposed. It is hypothesized that damage quantification techniques can be used to develop accurate creep, fatigue, and plastic/ductile cumulative- nonlinear- damage laws within the continuum damage mechanics principle. These damage laws when coupled with appropriate constitutive equations and a degrading stiffness tensor can be used to predict the mechanical state of a component. A series of monotonic, creep, fatigue, and tensile-hold creep-fatigue tests are obtained from literature for 304 stainless steel at 600°C (1112°F) in an air. Cumulative- nonlinear- creep, fatigue, and a coupled creep-fatigue damage laws are developed. The individual damage variables are incorporated as an internal state variable within a novel unified viscoplasticity constitutive model (zero yield surface) and degrading stiffness tensor. These equations are implemented as a custom material model within a custom FORTRAN one-dimensional finite element code. The radial return mapping technique is used with the updated stress vector solved by Newton-Raphson iteration. A consistent tangent stiffness matrix is derived based on the inelastic strain increment. All available experimental data is compared to finite element results to determine the ability of the unified mechanical model to predict deformation, damage evolution, crack growth, and rupture under a creep-fatigue environment.<br>Ph.D.<br>Doctorate<br>Mechanical and Aerospace Engineering<br>Engineering and Computer Science<br>Mechanical Engineering
38
Hogan, Erik A. "An efficient method for the optimization of viscoplastic constitutive model constants." Honors in the Major Thesis, University of Central Florida, 2009. http://digital.library.ucf.edu/cdm/ref/collection/ETH/id/1274.
Full textAbstract:
This item is only available in print in the UCF Libraries. If this is your Honors Thesis, you can help us make it available online for use by researchers around the world by following the instructions on the distribution consent form at http://library.ucf.edu/Systems/DigitalInitiatives/DigitalCollections/InternetDistributionConsentAgreementForm.pdf You may also contact the project coordinator, Kerri Bottorff, at kerri.bottorff@ucf.edu for more information.<br>Bachelors<br>Engineering and Computer Science<br>Aerospace Engineering
39
Brown, Stuart Bryan. "An internal variable constitutive model for the hot working of metals." Thesis, Massachusetts Institute of Technology, 1987. http://hdl.handle.net/1721.1/14824.
Full text
40
Wang, Shun-Sheng. "Development of constitutive model for Al-2011 alloy in mushy state." Ohio University / OhioLINK, 1994. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1174224280.
Full text
41
Kim, Dong-Gyou. "Development of a constitutive model for resilient modulus of cohesive soils." The Ohio State University, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=osu1078246971.
Full text
42
Rajasekaran, Nepolean. "A Nonlinear Constitutive Model for High Density Polyethylene at High Temperature." University of Cincinnati / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1298041213.
Full text
43
Wiseman, K. H. "Development of a constitutive model for a heaving clay from Rosebank." Master's thesis, University of Cape Town, 1993. http://hdl.handle.net/11427/8452.
Full textAbstract:
Bibliography: leaves 135-142.<br>Heaving clays are partially saturated soils composed of a high fraction of the montmorillonite clay mineral. When exposed to free water they undergo volumetric expansion, which often results in differential movements at the surface and damage to building structures founded on the clay. The economic consequences of such damage is severe. Heaving clay causes in excess of R100 million damage in South Africa each year, making it the country's most significant problem soil. The best method of dealing with a heaving clay is through appropriate design. This would be facilitated if methods such as finite element analysis were available to designers. The aim of this research project was to develop a constitutive model for an expansive clay which could be numerically implemented within the finite element method. A review of available literature on expansive clays showed that the heave strain that clay under an applied load will undergo can be expressed in terms of the parameters percent heave and heave pressure. These parameters are influenced by the degree of moisture changes experienced by the soil, and its dry density. Various different methods of establishing the percent heave and heave pressure have been proposed, but the values given by each differ due to the influence of different test stress paths on the results. More detailed examination of the effect of test stress path on the volume of heaving clays was therefore required to resolve the reasons for the differences in the test results, and to give a fuller understanding of the volumetric response of the material for the purposes of developing the constitutive model. Hence a series of laboratory tests was conducted on a clay from Rosebank in the Cape Province to investigate the effect of test stress path on the clay volume.
44
Abdelal, Gasser F. "A three-phase constitutive model for macrobrittle fatigue damage of composites." Morgantown, W. Va. : [West Virginia University Libraries], 2000. http://etd.wvu.edu/templates/showETD.cfm?recnum=1485.
Full textAbstract:
Thesis (Ph. D.)--West Virginia University, 2000.<br>Title from document title page. Document formatted into pages; contains xiii, 183 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 180-183).
45
Kim, Dong Gyou. "Development of a constitutive model for resilient modulus of cohesive soils." Columbus, Ohio : Ohio State University, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1078246971.
Full textAbstract:
Thesis (Ph. D.)--Ohio State University, 2004.<br>Title from first page of PDF file. Document formatted into pages; contains xxvi, 252 p.; also includes graphics. Includes abstract and vita. Co-advisors: Frank M. Croft and Tarunja S. Batalia, Dept. of Civil Engineering. Includes bibliographical references (p. 122-131).
46
Clarke, Samuel David. "Enhancement of the Brick constitutive model to incorporate viscous soil behaviour." Thesis, University of Sheffield, 2009. http://etheses.whiterose.ac.uk/158/.
Full textAbstract:
The Brick model is an advanced elasto-plastic constitutive model for soils and has become a recognised tool for modelling ground behaviour, following its implementation into the finite element program Safe. The model can reproduce many essential elements of soil behaviour, which is viewed from a strain-based perspective. An analogue for the model is that of a man walking around a room, pulling a number of bricks with strings of different lengths behind him. The room represents strain space, the man's movement is the applied strain and each brick movement is the response of a proportion of the soil. The present Brick model, although advanced, does not account for viscous behaviour, including creep and strain rate dependent stiffness, which can be very significant for clay soils. The principal aim of the work was to incorporate such behaviour into the Brick model. Two main approaches were identified manipulating either the velocity of the bricks or the string lengths. Both approaches were implemented into the Brick model allowing a series of tests to be conducted into their predictive capabilities. Isotach strain rate behaviour was investigated with both models by simulating both constant and step rate of strain tests. Simulations of past experimental work into the combined effects of creep and recent stress history on clay soil stiffness were also conducted. It was demonstrated, in accordance with the experiments, that creep can erase the effects on the initial stiffness of recent stress history involving relatively short stress paths approaching the current state, though this was not true for longer approach paths. The experimental results were more correctly simulated using the model with manipulated, strain rate dependent string lengths, the SRD Brick model. The SRD Brick model was then implemented into Safe to allow the analysis of two case histories, thereby quantifying the influence that viscous effects can have. The first involved the analysis of surface displacements above the westbound tunnel forming part of the Jubilee Line extension beneath St James's Park, London. The second analysis was concerned with the prediction of heave displacements of a deep basement in Horseferry Road, London. The SRD Brick model was able to significantly improve on the predictions given by the original Brick model in both cases.
47
Madaschi, Aldo. "A nonlinear viscoplastic double yield surface constitutive model for geologic materials." Doctoral thesis, Università degli studi di Trento, 2015. https://hdl.handle.net/11572/369021.
Full textAbstract:
A new constitutive model is proposed to describe the stress-strain-time behaviour of clays and organic soils. This approach is based on the framework of overstress viscoplastic theory and can be applied to any elastoplastic (inviscid) model.The most innovative idea of the proposed model is the identification of two components of strain for each deformation mechanism. In particular, in both the elastic and the plastic regimes a fast and a slow strain mechanism are assumed to be present. To this aim the constitutive model is based on two yield surfaces based on overstress viscoplasticity theory: one is quasi-instantaneous (for the fast part of plastic deformations) and the other is viscous (for the slow part of plastic deformations). This assumption permits the reliable simulation of the mechanical behaviour of a wide range of clayey soils: from inorganic clay (a.e. kaolinite and bentonite), to organic clays and peats. A further interesting aspect of the proposed model is the capability of simulate both the normally consolidated and the overconsolidated regime within a unique constitutive approach. An extensive experimental program on three different peaty soils has been performed to validate the constitutive model. The experimental tests include a wide range of oedometric tests (with very different loading conditions), and a series of triaxial tests conducted on NC and OC peats. The model has been validated also by simulating the settlements of a real embankment founded on a thick layer of organic clay.
48
Madaschi, Aldo. "A nonlinear viscoplastic double yield surface constitutive model for geologic materials." Doctoral thesis, University of Trento, 2015. http://eprints-phd.biblio.unitn.it/1513/1/Aldo_Madaschi_B5.pdf.
Full textAbstract:
A new constitutive model is proposed to describe the stress-strain-time behaviour of clays and organic soils. This approach is based on the framework of overstress viscoplastic theory and can be applied to any elastoplastic (inviscid) model.The most innovative idea of the proposed model is the identification of two components of strain for each deformation mechanism. In particular, in both the elastic and the plastic regimes a fast and a slow strain mechanism are assumed to be present. To this aim the constitutive model is based on two yield surfaces based on overstress viscoplasticity theory: one is quasi-instantaneous (for the fast part of plastic deformations) and the other is viscous (for the slow part of plastic deformations). This assumption permits the reliable simulation of the mechanical behaviour of a wide range of clayey soils: from inorganic clay (a.e. kaolinite and bentonite), to organic clays and peats. A further interesting aspect of the proposed model is the capability of simulate both the normally consolidated and the overconsolidated regime within a unique constitutive approach. An extensive experimental program on three different peaty soils has been performed to validate the constitutive model. The experimental tests include a wide range of oedometric tests (with very different loading conditions), and a series of triaxial tests conducted on NC and OC peats. The model has been validated also by simulating the settlements of a real embankment founded on a thick layer of organic clay.
49
Dabeet, Antone E. "A practical model for load-unload-reload cycles on sand." Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/4082.
Full textAbstract:
The behaviour of sands during loading has been studied in great detail. However, little
work has been devoted to understanding the response of sands in unloading. Drained
triaxial tests indicate that, contrary to the expected elastic behaviour, sand often exhibit
contractive behaviour when unloaded. Undrained cyclic simple shear tests show that the
increase in pore water pressure generated during the unloading cycle often exceeds that
generated during loading. The tendency to contract upon unloading is important in
engineering practice as an increase in pore water pressure during earthquake loading
could result in liquefaction.
This research contributes to filling the gap in our understanding of soil behaviour in
unloading and subsequent reloading. The approach followed includes both theoretical
investigation and numerical implementation of experimental observations of stress
dilatancy in unload-reload loops. The theoretical investigation is done at the micromechanical
level. The numerical approach is developed from observations from drained
triaxial compression tests. The numerical implementation of yield in unloading uses
NorSand — a hardening plasticity model based on the critical state theory, and extends
upon previous understanding. The proposed model is calibrated to Erksak sand and then
used to predict the load-unload-reload behaviour of Fraser River sand. The trends
predicted from the theoretical and numerical approaches match the experimental
observations closely. Shear strength is not highly affected by unload-reload loops.
Conversely, volumetric changes as a result of unloading-reloading are dramatic.
Volumetric strains in unloading depend on the last value of stress ratio (q/p’) in the
previous loading. It appears that major changes in particles arrangement occur once peak
stress ratio is exceeded. The developed unload-reload model requires three additional
input parameters, which were correlated to the monotonic parameters, to represent
hardening in unloading and reloading and the effect of induced fabric changes on stress
dilatancy. The calibrated model gave accurate predictions for the results of triaxial tests
with load-unload-reload cycles on Fraser River sand.
50
Llobet, Vallejo Jordi. "A constitutive model for fatigue and residual strength predictions of composite laminates." Doctoral thesis, Universitat de Girona, 2020. http://hdl.handle.net/10803/670692.
Full textAbstract:
This thesis investigates the fatigue behaviour of fibre-reinforced composite laminates. Fatigue of composite materials is a complex subject both from an experimental and numerical modelling point of view. In this context, we designed a quite extensive experimental campaign to investigate the failure mechanisms that occur when the composite material undergoes fatigue. Then, we developed a constitutive model to anticipate the mechanical behaviour and the final strength of the material. This model was implemented inside a finite element code in order to analyse the behaviour of composite structures under different loading scenarios. The final objective of this type of numerical tool is to reduce the number of test and time required for certification of aerospace composite parts<br>Aquesta tesi investiga la resposta a fatiga de laminats compòsits fabricats amb fibra de carboni. L'estudi de la fatiga en materials compòsits és un tema de gran complexitat tant des d'un punt de vista experimental com de modelització computacional. En aquest context, s'ha dissenyat una àmplia campanya experimental per investigar els mecanismes de dany que apareixen quan el material es sotmet a càrregues cícliques o a fatiga. Al mateix temps, s'ha desenvolupat un model constitutiu per anticipar la resposta estructural i la resistència final del material. Aquest model s'ha implementat dins d'un codi d'elements finits per tal d'analitzar estructures aeronàtutiques en diferent condicions de càrrega. L'objectiu final d'aquest models computacionals és la de reduir el nombre d'assajos experimentals i el temps que es necessita per certificar estructures aeronàutiques