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Dissertations / Theses on the topic 'Fracture parameter'

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Published: 9 March 2023
Last updated: 10 March 2023

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1

MacLennan, Iain James. "Two parameter engineering fracture mechanics." Thesis, University of Glasgow, 1996. http://theses.gla.ac.uk/6756/.

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The object of this work was to investigate and expand on previously carried out research into elastic-plastic crack tip fields using the first two terms of the Williams expansion to characterise the degree of crack tip constraint. As a precursor to this research a history of fracture mechanics is also presented. In the present work crack tip fields in small scale yielding have been detennined using modified boundary layer formulations in an attempt to model the influence of the second order term of the Williams expansion, the T -stress. The prime object of this thesis was to investigate and expand on previously carried out research into a two parameter characterisation of elastic-plastic crack tip fields using the second parameter of the Williams expansion(T), which attempts to characterise the degree of crack tip constraint. Modified Boundary Layer formulations in conditions of plane strain were implemented to derive a suitable reference solutions, against which the effects of out of plane strains can be compared and the validity of presently established reference fields can be gauged. The effect of out of plane non-singular stress, S, on the crack tip stress field were also considered, where constraint was largely determined by T. A wide range of analyses have been carried out, from the microstructural scale to complete engineering components in an attempt to characterise crack tip stress fields. The ability to apply two parameter fracture concepts to real engineering structures requires methods for calculating T for complex components with realistic semi-elliptical defects. A simple engineering method for achieving this was developed making use of linespring elements in the finite element package ABAQUS. This approach was validated by the calculation of T for semi-elliptical cracks at the chord-brace intersection of a tubular welded joint, modelled using the mesh generation program PATRAN. The micromechanics of cleavage, using the Ritchie-Knott-Rice model have also been constructed. This work relates the ratio of J for unconstrained and constrained geometries to critical microstructural distance, critical cleavage stress and the toughness ratio on the strainhardening effect. The elastic-plastic behaviour of short and deeply cracked bend bars has previously been described by Betegon and Hancock based on the first two terms of the Williams expansion. A local cleavage criterion has been applied to these fields to indicate the effect of loss of constraint on lower shelf toughness of shallow cracked bend bars. The work models the maximum temperature at which cleavage can occur in these geometries to show the effect of constraint and aJW ratio of cracked bend bars on the ductile-brittle transition temperature. This has also been backed by a significant experimental research program. Finally constraint dependent toughness has been considered in relation to failure assessment methodologies. A simple engineering method for modifying these Failure Assesssment Diagrams has been presented, this consists of considering the constraint matched toughness of the strucutre. This procedure recovers the original Failure Assessment Line and unifies the constraint dependent fracture toughness within defect assessment schemes which utilise Failure Assessment Diagrams.
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2

Yoon, Kee Bong. "Characterization of creep fatigue crack growth behavior using C[superscript](t[superscript]) parameter." Diss., Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/17523.

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3

Curtin, William J. "An investigation of a two parameter elastic-plastic fracture mechanics methodology." Thesis, Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/17782.

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4

Reakes, Clayton E. IV. "Nonlinear Fracture Mechanics Analysis of Threaded Fastener Geometry." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1447425945.

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5

Wert, Melissa Jane. "The applicability of modified J-integral as a fracture parameter for polycarbonate." Thesis, Georgia Institute of Technology, 1988. http://hdl.handle.net/1853/18860.

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6

MARTINELLI, MATTIA. "From outcrop to fracture model. A multidisciplinary approach to characterize fracture networks from outcrop analogues in carbonates affected by extensional tectonics." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2020. http://hdl.handle.net/10281/271026.

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I network di fratture hanno un ruolo fondamentale nel controllo della permeabilità e del flusso dei geo-fluidi (e.g. idrocarburi, acqua, fluidi idrotermali ecc.). Nel sottosuolo i parametri delle fratture vengono solitamente caratterizzati utilizzando dati di pozzo e dati sismici, i quali però sono divisi da un salto di scala. Infatti, i dati di pozzo sono sparsi e parziali mentre anche la sismica migliore non è in grado di identificare fratture con dimensione minori di 200 metri. Gli analoghi esumati con dimensioni chilometriche posso aiutare a colmare questo divario permettendo di raccogliere una grande quantità di dati a scale differenti. In questa tesi di dottorato abbiamo caratterizzato il network di fratture nei carbonati delle isole di Malta e Gozo, che si trovano all’interno della Piattaforma Pelagica nel foreland della catena Appeninico-Magrebide e sono degli spettacolari analoghi esumati di reservoir di idrocarburi fratturati sviluppatisi in ambienti tettonici estensionali. La stratigrafia delle isole maltesi è caratterizzata dalla presenza di differenti tipi di carbonati di età compresa tra il tardo Oligocene e il Miocene superiore., tagliati da due set di faglie normali (ENE-WSW e WNW-ESE) con rigetti verticali che possono raggiungere i 210 metri. Dicchi nettuniani associati a faglie normali con rigetto limitato (meno di 5 metri) sono inoltre presenti nelle unità più antiche. In questa tesi abbiamo utilizzato un approccio multidisciplinare che ci ha permesso di effettuare diversi tipi di studi che sono presentati nei quattro capitoli della tesi. i) Nel primo capitolo abbiamo ricostruito l’evoluzione tettonica e geodinamica delle isole di Malta e Gozo e della Piattaforma Pelagica a partire dal tardo Oligocene fino al Pliocene. Questo ci ha permesso inoltre di ricostruire l’età di formazione e la cinematica dei diversi set di faglie e fratture. ii) Nel secondo capitolo abbiamo caratterizzato i parametri delle fratture assieme al loro impatto sulla connettività idraulica e l’architettura della zona di danneggiamento legata alla faglia di Qala (Gozo). Per fare questo abbiamo applicato un nuovo workflow che combina scan-line lineari con scan-area applicate su modelli di affioramento digitali di dimensioni chilometri utilizzando inoltre metodi automatici per il calcolo dei parametri della fratturazione. iii) Nel terzo capitolo, abbiamo mostrato come la meccanica stratigrafica e in particolare le proprietà elastiche delle rocce giochino un ruolo fondamentale nel controllo dello spessore della damage zone. I risultati sono stati ottenuti combinando osservazioni di terreno con analisi petro-fisiche, petrografiche, geo-meccaniche e modelli numerici. iv) Nel quarto capitolo abbiamo utilizzato il Volume Elementare Rappresentativo del network di fratture caratterizzato durante lo studio effettuato nel capitolo due per realizzare modelli DFN ad una scala più piccola rispetto a quella del reservoir. Questo ci ha permesso di risolvere diversi problemi legati alla modellazione della fratturazione alla scala del reservoir.
Fracture networks exert a primary role in the control of permeability and flow of geo-fluids (e.g hydrocarbons, ground water, hydrothermals fluid, etc.). Fracture parameters in the subsurface are usually characterised using borehole and seismic data, but these are affected by a scale gap. Well data are only sparse and partial and even the best seismic data cannot detect fractures shorter than ca 200 m. Km-scale outcrop analogues can help to fill this gap, allowing to collect huge amounts of of data at different scales. This PhD thesis investigates the fracture networks in carbonates of the Maltese Islands, located in the Pelagian Platform in the foreland of the Sicilian-Appenine-Maghrebian fold and thrust belt, that are world-class analogues of extensional fractured and faulted hydrocarbon reservoirs. Here a Late-Oligocene – Late Miocene carbonatic sequence composed by different types of carbonates is exposed. It is cross-cut by normal faults with a vertical displacement up to 210 meters, arranged in two main sets striking ENE-WSW and WNW-ESE. Moreover, Neptunian dykes associated with small normal faults (less than 5 meters of displacement) are present in the lower units. We applied a multidisciplinary approach that allowed us to carry out the following studies that are presented in the four chapters of these thesis. i) In the first chapter, we characterize the tectonic and geodynamic evolution of the Maltese Islands and Pelagian Platform from the Late Oligocene to the Pliocene and to understand the timing, kinematics and stress regime of the different fault and joint sets. ii) In the second chapter, we Investigate the fracture parameters and their impact on hydraulic connectivity and the architecture of the damage of the Qala fault (Gozo). The study was performed applying a new workflow that combines linear scanlines and scanareas collected on a large Digital Outcrop Model also using automatic methods for the extraction of fracture parameters. iii) In the third chapter, we investigate the control of the mechanical stratigraphy and in particular of the elastic properties of the rocks on the damage zone thickness combining petrographical, petrophysical, geomechanical and numerical modeling analyses. iv) In the fourth chapter, we characterize the Representative Elementary Volume of fracture network parameters extracted from the DOM study to drive Discrete Fracture Network modeling. This allows building DFN models on in order to build DFN model on a smaller scale with respect to the reservoir scale solving many numerical models.
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7

Wang, Yongyi. "A two-parameter characterization of elastic-plastic crack tip fields and applications to cleavage fracture." Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/13461.

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8

Hosseinian, Armin. "Numerical simulations of fluid flow through a single rough walled fracture." Thesis, Curtin University, 2011. http://hdl.handle.net/20.500.11937/1764.

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The morphological properties of rock fractures may have a significant influence on their hydromechanical behaviour. Fracture surface roughness could change the fluid flow regime from laminar to turbulent, while it causes the flow properties to deviate from cubic law for smooth channels due to a change in fracture equivalent hydraulic aperture. Different empirical (including the well known Joint Roughness Coefficient, JRC) and statistical methods have been proposed for surface roughness characterisation in an attempt to link them to the hydromechanical behaviour of fractures.This thesis aims to investigate the potential for assessment of fluid behaviour by studying its surface geometrical properties. D[subscript]R[subscript]1 and D[subscript]R[subscript]2, the 2D and 3D roughness parameters developed recently using Riemannian geometry, were used to correlate fracture geometry to its flow behaviour. Also, the 2D Riemannian isotropy parameter (I[subscript]R[subscript]2) was used to correlate surface roughness anisotropy with directionality in fluid flow behaviour along different directions.Numerical simulations in both 2D and 3D were performed assuming the laminar flow regime using FLUENT software. This assumption is, to a large extent, acceptable for situations where the height to length ratios of a fracture is very small. 2D analysis of synthetic profiles with different geometries demonstrated how a change in profile roughness can affect flow response, for example, the pressure drop. JRC flow channels developed in this work as combinations of pairs of JRC profiles were simulated numerically. The analysis results indicated that channels with a similar JRC average for the upper and lower walls but a different JRC profile number responded differently when they were subjected to fluid flow. Therefore, assuming special fluid properties, correlations developed using the pressure drop of a fracture can be estimated by its analogy to JRC flow channels.3D simulations of a corrugated plane were performed assuming different asperity height distributions, for fluid travelling along different directions with respect to surface geometry and at different shear displacements. No asperity contact and failure is assumed in the analysis performed in this work. D[subscript]R[subscript]2 analysis results of the corrugated plane indicated how fluid flow could be related to surface geometry. For instance, it was observed that the pressure drop was maximised along the direction of maximum roughness and reduced to its minimum along a perpendicular direction which shows anisotropy in fluid flow behaviour. Significant changes in pressure drop due to shear offset indicated the importance of fracture wall displacements with respect to each other. A detailed analysis of one synthetically generated surface, and also five surfaces with identical statistical parameters except their correlation distances being different, further confirmed the above concepts. This was followed by analysing a real rock like fracture which was studied elsewhere for fracture shear tests in the lab. Simulation of this surface was performed with particular interest in identifying the locations where the velocity magnitude reduced to nearly zero after the fracture was subjected to a shear offset corresponding to maximum shear stress. These areas were found to be very similar to the locations of asperity degradations as observed through lab experiments. The roughness analysis of the surface was in agreement with the correlation found between the mechanical and hydraulic behaviour of the surface.The results of this research demonstrate how detailed analysis of surface geometry could provide valuable information with respect to surface flow behaviour. Detailed discussions and interpretations of the results will be presented and various conclusions will be made.
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9

WATANABE, Katsuhiko, and Hideyuki AZEGAMI. "Proposal of a New Crack Model Considering the Discontinuity in the Cracked Plane and Its Application to the Evaluation of Crack Parameter." 日本機械学会, 1986. http://hdl.handle.net/2237/12161.

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10

渡辺, 勝彦, Katsuhiko Watanabe, 秀幸 畔上, and Hideyuki Azegami. "き裂前縁を含む面の非連続性を考慮したき裂モデルの提案とそのき裂パラメータ評価への適用." 日本機械学会, 1985. http://hdl.handle.net/2237/7227.

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11

Shukla, Pratik P. "Viability and characterization of the laser surface treatment of engineering ceramics." Thesis, Loughborough University, 2011. https://dspace.lboro.ac.uk/2134/8426.

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Laser surface treatment of engineering ceramics offers various advantages in comparison with conventional processing techniques and much research has been conducted to develop applications. Even so, there still remains a considerable gap in knowledge that needs to be filled to establish the process. By employing a fibre laser for the first time to process silicon nitride (Si3N4) and zirconia (ZrO2) engineering ceramics, a comparison with the CO2 and a Nd:YAG lasers was conducted to provide fundamental understanding of various aspects of the laser beam-material interaction. Changes in the morphology, microstructure, surface finish, fracture toughness parameter (K1c) were investigated, followed by thermal finite element modelling (FEM) of the laser surface treatment and the phase transformation of the two ceramics, as well as the effects of the fibre laser beam parameter - brightness (radiance). Fibre and CO2 laser surface treatment of both Si3N4 and ZrO2 engineering ceramics was performed by using various processing gases. Changes in the surface roughness, material removal, surface morphology and microstructure were observed. But the effect was particularly more remarkable when applying the reactive gases with both lasers and less significant when using the inert gases. Microcracking was also observed when the reactive gases were applied. This was due to an exothermic reaction produced during the laser-ceramic interaction which would have resulted to an increased surface temperature leading to thermal shocks. Moreover, the composition of the ceramics was modified with both laser irradiated surfaces as the ZrO2 transformed to zirconia carbides (ZrC) and Si3N4 to silicon dioxide (SiO2) respectively. The most appropriate equation identified for the determination of the fracture toughness parameter K1c of the as-received, CO2 and the fibre laser surface treated Si3N4 and ZrO2 was K1c=0.016 (E/Hv) 1/2 (P/c3/2). Surfaces of both ceramics treated with CO2 and the fibre laser irradiation produced an increased K1c under the measured conditions, but with different effects. The CO2 laser surface treatment produced a thicker and softer layer whereas the fibre laser surface treatment increased the hardness by only 4%. This is inconsiderable but a reduction in the crack lengths increased the K1c value under the applied conditions. This was through a possible transformation hardening which occurred within both engineering ceramics. Experimental findings validated the generated thermal FEM of the CO2 and the fibre laser surface treatment and showed good agreement. However, a temperature difference was found between the CO2 and fibre laser surface treatment due to the difference in absorption of the near infra-red (NIR) wavelength of the fibre laser being higher than the mid infra-red (MIR) wavelength of the CO2 laser. This in turn, generated a larger interaction zone on the surface that was not induced further into the bulk, as was the case with the fibre laser irradiation. The MIR wavelength is therefore suitable for Viability and Characterization of the Laser Surface Treatment of Engineering Ceramics 3 the surface processing of mainly oxide ceramics and surface treatments which do not require deep penetration. Phase transformation of the two ceramics occurred at various stages during the fibre laser surface treatment. The ZrO2 was transformed from the monoclinic (M) state to a mixture of tetragonal + cubic (T+C) during fibre laser irradiation and from T+C to T and then a partially liquid (L) phase followed by a possible reverse transformation to the M state during solidification. The Si3N4 transformed to a mixture of α-phase and β-phase (α→ α+β) followed by α+β and fully transforms from α+β → β-phase. What is more, is a comparison of the fibre laser-beam brightness parameter with that of the Nd:YAG laser. In particular, physical and microstructural changes due to the difference in the laser-beam brightness were observed. This research has identified the broader effects of various laser processing conditions, as well as characterization techniques, assessment and identification of a method to determine the K1c and the thermal FEM of laser surface treated engineering ceramics. Also, the contributions of laser-beam brightness as a parameter of laser processing and the influence thereof on the engineering ceramics have been identified from a fundamental viewpoint. The findings of this research can now be adopted to develop ceramic fuel cell joining techniques and applications where laser beam surface modification and characterization of engineering ceramics are necessary.
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12

Rasche, Stefan. "Bestimmung von Materialparametern der elastisch-plastischen Verformung und des spröden Versagens aus Small-Punch-Kleinstproben." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2013. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-116905.

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Der Small-Punch-Test (SPT) ist eine vielversprechende minimalinvasive mechanische Prüfmethode, wenn nur sehr wenig Material für Proben zur Verfügung steht. Die vorliegende Arbeit hat das Ziel, aus Small-Punch-Kleinstproben wahre Materialparameter der elastisch-plastischen Verformung und des spröden Versagens zu bestimmen. Die Kraft-Verschiebungs-Kurve des Versuchs stellt die nichtlineare Materialantwort der inhomogen beanspruchten Probe dar. Das inverse Problem der Identifikation konstitutiver Materialparameter wird numerisch mit Hilfe von Finite-Elemente-Simulationen in Verbindung mit einem Response-Surface-Modell und nichtlinearer Optimierungsverfahren gelöst, indem die Abweichung zwischen gemessener und simulierter Kurve minimiert wird. Mit Hilfe einer eigens entwickelten Kühlapparatur wurden Versuche mit ferritischen Stählen von Raumtemperatur bis hinunter zu -191°C durchgeführt und die temperaturabhängigen Fließkurven identifiziert. Bei tiefen Temperaturen wurden die Weibull-Parameter der zufällig streuenden Sprödbruchfestigkeit bestimmt und die Bruchzähigkeitsverteilung durch Simulation einer CT-Probe vorhergesagt. Für eine Aluminiumoxidkeramik wurden ebenfalls die Weibull-Parameter bestimmt sowie mit Indenterrissen versehene Proben zur Abschätzung der Bruchzähigkeit verwendet
The small punch test (SPT) is a promising minimally invasive material testing method, especially in cases where only small amounts of material are available. This thesis is aimed at identifying true material parameters of elastic-plastic deformation and brittle fracture. The load-displacement curve of the test represents the non-linear material response of the nonuniformly stressed specimen. The identification of material parameters of constitutive laws is an inverse problem, which is solved numerically. Finite element simulations together with a response surface model and nonlinear optimization techniques are applied to minimize the error between measured and simulated curves. A specially developed cooling apparatus was used to perform tests with ferritic steels from room temperature down to -191°C. The temperature dependent yield stresses and hardening curves were identified. At low temperatures the Weibull parameters of randomly distributed cleavage fracture strength were estimated. The fracture toughness distribution was then predicted by the help of a finite element simulation of a CT specimen. Furthermore the Weibull parameters of an alumina ceramic were determined and its fracture toughness was predicted using specimens prepared with indentation cracks
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13

Smith, Daniel J. "Rapid determination of temperature-dependent parameters for the crystal viscoplasticity model." Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/43670.

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Thermomechanical fatigue life prediction is important in the design of Ni-base superalloy components in gas turbine engines and requires a stress-strain analysis for accurate results. Crystal viscoplasticity models are an ideal tool for this stress-strain analysis of Ni-base superalloys as they can capture not only the anomalous yielding behavior, but also the non-Schmid effect, the strain rate dependence, and the temperature dependence of typically large grained directionally-solidified and single crystal alloys. However, the model is difficult to calibrate even for isothermal conditions because of the interdependencies between parameters meant to capture different but similar phenomena at different length scales, many tied to a particular slip system. The need for the capacity to predict the material response over a large temperature range, which is critical for the simulation of hot section gas turbine components, causes the determination of parameters to be even more difficult since some parameters are highly temperature dependent. Rapid parameter determination techniques are therefore needed for temperature-dependent parameterizations so that the effort needed to calibrate the model is reduced to a reasonable level. Specific parameter determination protocols are established for a crystal viscoplasticity model implemented in ABAQUS through a user material subroutine. Parameters are grouped to reduce interdependencies and a hierarchical path through the groups and the parameters within each group is established. This dual level hierarchy creates a logical path for parameter determination which further reduces the interdependencies between parameters, allowing for rapid parameter determination. Next, experiments and protocols are established to rapidly provide data for calibration of the temperature-dependencies of the viscoplasticity. The amount of data needed to calibrate the crystal viscoplasticity model over a wide temperature range is excessively large due to the number of parameters that it contains which causes the amount of time spent in the experimentation phase of parameter determination to be excessively large. To avoid this lengthy experimentation phase each experiment is designed to contain as much relevant data as possible. This is accomplished through the inclusion of multiple strain rates in each experiment with strain ranges sufficiently large to clearly capture the inelastic response. The experimental and parameter determination protocols were exercised by calibrating the model to the directionally-solidified Ni-bas superalloy DS-CM247LC. The resulting calibration describes the material's behavior in multiple loading orientations and over a wide temperature range of 20 °C to 1050 °C. Several parametric studies illustrate the utility of the calibrated model.
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14

Hao, Bin. "Use of fracture mechanics parameters to characterize comminution." Master's thesis, This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-02162010-020306/.

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15

Kraus, Michael A. [Verfasser], Geralt [Akademischer Betreuer] [Gutachter] Siebert, Jens [Gutachter] Schneider, and Gerhard [Gutachter] Müller. "Machine Learning Techniques for the Material Parameter Identification of Laminated Glass in the Intact and Post-Fracture State / Michael A. Kraus ; Gutachter: Geralt Siebert, Jens Schneider, Gerhard Müller ; Akademischer Betreuer: Geralt Siebert ; Universität der Bundeswehr München, Fakultät für Bauingenieurwesen und Umweltwissenschaften." Neubiberg : Universitätsbibliothek der Universität der Bundeswehr München, 2019. http://d-nb.info/1183739559/34.

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16

Kraus, Michael A. Verfasser], Geralt [Akademischer Betreuer] [Gutachter] [Siebert, Jens [Gutachter] Schneider, and Gerhard [Gutachter] Müller. "Machine Learning Techniques for the Material Parameter Identification of Laminated Glass in the Intact and Post-Fracture State / Michael A. Kraus ; Gutachter: Geralt Siebert, Jens Schneider, Gerhard Müller ; Akademischer Betreuer: Geralt Siebert ; Universität der Bundeswehr München, Fakultät für Bauingenieurwesen und Umweltwissenschaften." Neubiberg : Universitätsbibliothek der Universität der Bundeswehr München, 2019. http://d-nb.info/1183739559/34.

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17

Que, Norbert S. Civil &amp Environmental Engineering Faculty of Engineering UNSW. "Identification of cohesive crack fracture parameters using mathematical programming." Awarded by:University of New South Wales. School of Civil and Environmental Engineering, 2003. http://handle.unsw.edu.au/1959.4/19189.

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This thesis is concerned with the characterisation of the parameters governing the tension-softening relations of the cohesive crack model. Parameter identification is an important area in fracture mechanics as it enables the use of a fracture model for the simulation of fracture processes in structures. Research, however, has shown that such a task is not trivial and continues to pose challenging problems to experimentalists and analysts alike. This dissertation presents general and efficient indirect methods for the characterisation of mode I fracture parameters defining the cohesive crack model. The identification problem is formulated as a special type of inverse problem. The formulation is in the form of a constrained optimisation problem known as a mathematical program with equilibrium constraints characterised, in the present instance, by complementarity conditions involving the orthogonality of two-sign constrained vectors. The solution of such a mathematical program is computationally challenging as it is disjunctive and nonconvex by nature. A number of nonlinear programming based approaches are proposed, after appropriate reformulation of the mathematical program as an equivalent nonlinear programming problem. Actual experimental data are used to validate and determine the most suitable algorithm for parameter identification. It was found that the smoothing-based method is by far superior than other schemes. As the problem is nonconvex and the nonlinear program can only guarantee a local or stationary point, global optimisation procedures are introduced in order to verify the accuracy of the solutions obtained by the algorithm. Two evolutionary search methods capable of finding the global optimum are implemented for parameter identification. The results generated by the evolutionary search techniques confirm the reliability of the solutions identified by the best nonlinear programming algorithm. All computations carried out in the thesis suggest the suitability and robustness of the selected algorithm for parameter identification.
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18

LIN, CHUNG-YI. "Determination of the Fracture Parameters in a StiffenedComposite Panel." NCSU, 2000. http://www.lib.ncsu.edu/theses/available/etd-20001122-103139.

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A modified J-integral, namely the equivalent domain integral, is derived for athree-dimensional anisotropic cracked solid to evaluate the stress intensity factor alongthe crack front using the finite element method. Based on the equivalent domain integralmethod with auxiliary fields, an interaction integral is also derived to extract the secondfracture parameter, the T-stress, from the finite element results. The auxiliary fields arethe two-dimensional plane strain solutions of monoclinic materials with the plane ofsymmetry at x3=0 under point loads applied at the crack tip. These solutions areexpressed in a compact form based on the Stroh formalism. Both integrals can beimplemented into a single numerical procedure to determine the distributions of stressintensity factor and T-stress components, T11, T13, and thus T33, along a three-dimensionalcrack front.The effects of plate thickness and crack length on the variation of the stressintensity factor and T-stresses through the thickness are investigated in detail for through-thicknesscenter-cracked plates (isotropic and orthotropic) and orthotropic stiffenedpanels under pure mode-I loading conditions. For all the cases studied, T11 remainsnegative. For plates with the same dimensions, a larger size of crack yields largermagnitude of the normalized stress intensity factor and normalized T-stresses. The resultsin orthotropic stiffened panels exhibit an opposite trend in general. As expected, for thethicker panels, the fracture parameters evaluated through the thickness, except the regionnear the free surfaces, approach two-dimensional plane strain solutions. In summary, thenumerical methods presented in this research demonstrate their high computationaleffectiveness and good numerical accuracy in extracting these fracture parameters fromthe finite element results in three-dimensional cracked solids.

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19

Yang, Lin. "Fracture mechanics parameters for cracks on non-planar interfaces." Diss., Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/17659.

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20

CALAND, VERONICA DE SOUZA. "EXPERIMENTAL RESULTS OF FRACTURE PARAMETERS FOR HIGH PERFORMANCE CONCRETE." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2001. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=1995@1.

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COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
A utilização mais freqüente dos concretos de alto desempenho na Construção Civil exige um melhor conhecimento sobre o comportamento deste material e a verificação de possíveis modificações no dimensionamento de elementos estruturais, como a consideração do efeito de escala. Recentemente, os conceitos da teoria da mecânica da fratura para a análise do comportamento das estruturas começaram a ser utilizados. A energia de fraturamento passa a ser uma propriedade intrínseca do material, fundamental no controle da resistência à flexão e ao cisalhamento Os principais objetivos desta dissertação são: obter experimentalmente os parâmetros de fraturamento para concretos de alto desempenho através da realização de ensaios estáveis e comparar estes resultados com resultados numéricos e experimentais encontrados na literatura. A metodologia utilizada para a determinação destes parâmetros é apresentada no trabalho. Foram executados ensaios estáveis à flexão em três pontos em vigas de concreto simples com entalhe, de acordo com as especificações elaboradas pela recomendação do comitê RILEM 50-FMC. As vigas foram moldadas no Laboratório de Estruturas da PUC- Rio e os ensaios realizados no Instituto de Tecnologia (ITUC) desta Universidade. Os ensaios foram realizados com controle de deslocamento da abertura do entalhe em uma máquina servo-hidráulica Instron modelo 8502. Foram ensaiadas 75 vigas, em quatro tamanhos diferentes, com alturas variando de 38 mm a 304 mm. A espessura das vigas foi mantida constante e igual a 38 mm. Os concretos utilizados apresentaram fator água/cimento entre 0,25 e 0,37 e resistência à compressão entre 70 MPa e 90 MPa.
The increasing use of high performance concrete in civil construction demands better knowledge of the behavior of this material and the review of possible changes in the design of structural elements, like the size effect. The concepts of the theory of fracture mechanics for the analysis of structures started to be used in recent days. The fracture energy became an inherent property of the material, and it is basic for the control of the nominal flexural strength and the modulus of rupture. The main purposes of this dissertation are to achieve experimentally the fracture parameters for high performance concrete by performing stable tests, and to carry out a comparison with numerical and experimental results found in literature. The methodology used for determining of these parameters is introduced in the work.Stable three-point bend tests were conducted in notched beams made with unreinforced concrete. These tests comply with the specifications given by the RILEM 50- FMC committee. The beams were cast at PUC-Rio Structural Laboratory and the tests were conducted at the Technology Institute (ITUC) of this University. The tests were performed using crack mouth opening displacement control in a closed-loop servohydraulic Instron machine model 8502. The experiments involved the testing of 75 singlenotched beams with four different sizes with depths varying from 38 mm to 304 mm. The thickness of the beams was kept constant and equal to 38 mm. The concrete had a watercement ratio varying from 0.37 to 0.25 and compressive strength between 70 MPa and 90 MPa.
La utilización más frecuente de los concretos de alto desempeño en la Construción Civil exige un mejor conocimiento sobre el comportamiento de este material y la verificación de posibles modificaciones en el dimensionamiento de elementos extructurales, como la consideración de la escala. Recientemente, los conceptos de la teoría de la mecánica de la fractura para el análisis del comportamiento de las extructuras comezaron a ser utilizados. La energía de fractura pasa a ser una propriedad intrínseca del material, fundamental en el control de la resistencia a la flexión y al cisallamento Los principales objetivos de esta disertación son: obtener experimentalmente los parámetros de fractura para concretos de alto desempeño a través de la realización de ensayos estables y comparar estos resultados con los resultados numéricos y experimentales encontrados en la literatura. LA metodología utilizada para la determinación de estos parámetros se presenta en el trabajo. Se ejecutaron ensayos estables a la flexión en tres puntos en vigas de concreto simple con entalle, de acuerdo con las especificaciones elaboradas por la recomendación del comité RILEM 50 FMC. Las vigas fueron moldadas en el Laboratorio de Extructuras de la PUC Rio y los ensayos realizados en el Instituto de Tecnología (ITUC) de esta Universidad. Los ensayos fueron realizados con control de desplazamiento de la abertura del entalle en una máquina servo hidráulica Instron modelo 8502. Fueron utilizadas 75 vigas, en cuatro tamaños diferentes, con alturas variando de 38 mm la 304 mm. Se mantuvo la espesura de las vigas constante e igual la 38 mm. Los concretos utilizados presentaran factor agua/cemento entre 0,25 y 0,37 y resistencia a la compresión entre 70 MPa y 90 MPa.
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21

Ekman, Matthew J. "Automated photoelastic determination of fracture parameters for bimaterial interface cracks." Thesis, Loughborough University, 1998. https://dspace.lboro.ac.uk/2134/10421.

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This thesis details an experimental study on the determination of the fracture parameters for a crack located at the interface between two dissimilar materials using the method of photoelasticity. The interface is potential1y an inherent weak spot of any composite material, structure"or adhesively bonded joint. Accurate description of the state of stress at the crack tip is required for strength prediction. The concept of the complex stress intensity factor is used to characterise the elastic crack tip stress field for an interface crack. Complex stress intensity factors and their moduli have been measured experimental1y for standard bimaterial crack geometries using the wel1 established technique of photo elasticity. Bimaterial specimens comprising aluminium al10y and epoxy resin components were used. This creates a large material mismatch at the interface and al10ws data to be col1ected from the epoxy component of the specimen using transmission photoelasticity. An automated ful1 field photoelastic technique was developed to significantly reduce the data col1ection time. The technique comprises elements from the approaches of three wavelength and phase stepping photoelasticity and is a significant improvement on techniques previously available. Stress intensity factors were determined by fitting a theoretical stress field solution for the bimaterial crack to the experimental data. A computational routine automatical1y selects the region of best fit between the experimental data and the theoretical solution. This data is then used to determine the complex stress intensity factor and its modulus value. In order to provide a robust fit between the experimental data and the theoretical field solution a weighting function was incorporated into the routine. The measured bimaterial stress intensity factors are compared with those determined experimental1y for equivalent homogeneous specimens made from epoxy resin. The differences between the two are then discussed. The experimental results agree with the wel1 known concept that tension and shear effects are inherently coupled at the crack tip. However, the effects of changing the load angle with respect to the interface also demonstrate that some contrasts exist with known numerical solutions.
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22

Hrstka, Miroslav. "Evaluation of Fracture Mechanical Parameters for Bi-Piezo-Material Notch." Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2019. http://www.nusl.cz/ntk/nusl-399212.

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Předkládaná dizertační práce se zabývá stanovením hlavních členů Williamsova asymptotického rozvoje popisujícího rovinné elektro-elastické pole v okolí piezoelektrických bi-materiálových vrubů a trhlin na rozhraní za použití rozšířeného Lechnického-Eshelbyho-Strohova formalismu v návaznosti na čistě anizotropní pružnost. Je ukázáno, že rozšířený Lechnického-Eshelbyho-Strohův formalismus představuje spolu s moderními programovacími koncepty v jazyku Python efektivní a také praktický nástroj pro lomovou analýzu piezoelektrických bi-materiálů. Teoretická část práce popisuje aspekty anizotropní pružnosti a její návaznost na piezoelektrické materiály. Základní rovnice zaměřené na speciální typy monoklinických materiálů, které umožňují oddělení rovinného a anti-rovinného problému, jsou vyjádřeny pomocí komplexních potenciálů. V praktické části práce je sestaven problém vlastního hodnot pro bi-materiálový vrub, na jehož základě jsou stanoveny exponenty singularity a pomocí dvoustavového -integrálu také zobecněné faktory intenzity napětí. Veškeré vztahy a numerické procedury jsou následně rozšířeny na problém piezoelektrických bi-materiálových vrubů a podrobně prozkoumány v uvedených příkladech. Zvláštní pozornost je věnována přechodu asymptotického řešení téměř zavřených vrubů a trhlin na rozhraní. Vliv směru polarizace na asymptotické řešení je také zkoumán. Přesnost stanovení zobecněných faktorů intenzity napětí je testována srovnáním asymptotického řešení a řešení získaného pomocí metody konečných prvků s velmi jemnou sítí konečných prvků. Na závěr je formalismus modifikován pro nepiezoelektrické materiály.
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23

Macdonald, Vincent. "Détermination d’un critère de rupture des gaines de Zircaloy-4 détendu hydruré contenant un blister d’hydrures, en conditions d’accident d’injection de réactivité." Thesis, Paris Sciences et Lettres (ComUE), 2016. http://www.theses.fr/2016PSLEM038/document.

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Cette étude porte sur la détermination d’un critère de rupture des gaines de combustible de Zircaloy-4 détendu hydruré contenant un blister d’hydrures, en conditions accidentelles représentatives d’un accident d’injection de réactivité. Deux plages de comportement différentes en fonction de la température ont clairement été mises en évidence grâce à l’étude bibliographique, aux différentes campagnes d’essais mécaniques et aux analyses des faciès de rupture des éprouvettes rompues : une rupture de type fragile pour la gaine à 25°C et une rupture ductile à 350°C.A 25°C, la rupture fragile a été traitée par une analyse globale en mécanique élasto-plastique de la rupture. A partir des essais mécaniques effectués à 25°C sur les gaines contenant des blisters, des simulations numériques par éléments finis ont été réalisées avec le code CAST3M. Des calculs d’intégrales-J en pointe de fissure ont alors permis d’identifier un critère de rupture en ténacité moyenne de 13,8 +/- 3,1 MPa.m1/2.A 350°C, une campagne d’essais biaxés de type pression interne couplée à la traction axiale a été réalisée sur des tronçons de Zircaloy-4 contenant des blisters, à des biaxialités des contraintes représentatives du RIA. Il a été montré que la rupture de la gaine, avec et sans blister, avait lieu de façon ductile, que la déformation diamétrale à rupture de la gaine diminuait lorsque la profondeur de blister augmentait, et que la biaxialité des contraintes n’avait pas d’effet sur la rupture des gaines contenant un blister suffisamment profond.Un modèle d’endommagement ductile couplé à la plasticité, basé sur un formalisme de type GTN, a été utilisé. Afin d’améliorer la description de l’endommagement des gaines de Zircaloy-4, une nouvelle source de germination de porosités liée au paramètre de Lode a été intégrée dans le modèle. L’évaluation de la triaxialité des contraintes et du paramètre de Lode dans les simulations numériques de la rupture ductile des gaines à 350°C a notamment permis de comprendre certaines tendances expérimentales
This study deals with the determination of a fracture criterion for hydrided, cold worked and stress relieved Zircaloy-4 fuel cladding tubes with hydride blister, during a reactivity initiated accident. Two types of fracture profiles were identified, depending on the temperature, thanks to a bibliographical study, mechanical tests and fracture profiles analysis : brittle fracture at 25°C, and ductile fracture at 350°C.At 25°C, brittle fracture was studied by a global analysis in elasto-plastic fracture mechanic. Numerical simulations were performed by a finite element method with the CAST3M code, based on mechanical tests on fuel cladding tubes with blisters. Crack tip J-integral calculations were carried out to identify a mean fracture toughness of 13,8 +/- 3,1 MPa.m1/2.At 350°C, internal pressure combined to axial tensile tests were performed on Zircaloy-4 fuel cladding tubes with hydride blisters, at stress biaxialities corresponding to those of a RIA. It was observed a ductile fracture for tubes with and without blister. It was shown that hoop strain at failure decreases when blister thickness increases, and that stress biaxiality has no effect on cladding tubes bearing a thick blister. A ductile fracture model based on the GTN model was employed and a nucleation of voids due to shear stress was introduced, based on the Lode parameter. Stress triaxiality and Lode parameter were assessed in numerical simulations to understand some experimental observations
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24

Sajjadian, Valiahmad. "Gravity drainage : microscopic studies and free fall in fractured reservoirs." Thesis, Heriot-Watt University, 1999. http://hdl.handle.net/10399/595.

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25

Healy, David. "Fracture prediction and the inversion of fault parameters using elastic dislocation theory." Thesis, University of Liverpool, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.402306.

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26

Koutsolelos, Evangelos. "Numerical analysis of a shear ram and experimental determination of fracture parameters." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/74982.

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Thesis (Nav. E. and S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 127-129).
The human, economic and environmental disaster that followed the Deepwater Horizon catastrophe at the Gulf of Mexico in April 2010 revealed how much the offshore drilling industry relies on the Blowout Preventer (BOP) as the primary means of controlling a 'well kick' or 'blowout'. One of the most important components of the BOP are the shear rams which are tasked with cutting the drilling string in case of an emergency, allowing the blind rams and the annular type blowout preventer to seal the wellbore and generally prevent things from becoming unmanageable. The increased drill pipe material strength, the fact that its diameter and wall thickness are eventually optimized (larger and heavier pipe sizes) and the greater water depths in combination with the high drilling fluid density affect the BOP's ability to shear. This study investigates all stages of the shearing process and attempts to optimize the geometry of the shear blades. In order to do that, simulations are conducted with Finite Element Models (FEM) by utilizing the Impact and Crashworthiness Lab's (ICL) fracture methodology, the backbone of which is the Modified Mohr-Coulomb (MMC) fracture criterion. Nine cases which involve three different angles defining the sharpness (cutting angle) and three angles characterizing the shape of the blades are evaluated. The optimum configurations for the shear blades are investigated based on the maximum required cutting force and the sealing capability. The simulations are performed for the TRIP 690 steel as well as for the X70 grade steel. The fracture and plasticity parameters for the X70 grade steel are experimentally determined in the ICL lab as part of this research. In addition, recommendations for shearing the tool joints, the connections of the drill pipes, are made based on the Finite Element (FE) simulations. Finally, as a second application of the MIT's fracture prediction capability, the process of fracture of a pre-cracked drill pipe is solved numerically and compared with the response of an uncracked drill pipe.
by Evangelos Koutsolelos.
Nav.E.and S.M.
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27

Deng, Hailin. "Upscaling reactive transport parameters for porous and fractured porous media." Tallahassee, Florida : Florida State University, 2009. http://etd.lib.fsu.edu/theses/available/etd-10292009-103844/.

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Thesis (Ph. D.)--Florida State University, 2009.
Advisor: Ming Ye, Zhenxue Dai, Florida State University, College of Arts and Sciences, Dept. of Geological Sciences. Title and description from dissertation home page (viewed on Apr. 26, 2010). Document formatted into pages; contains xxii, 167 pages. Includes bibliographical references.
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28

Bejček, Michal. "Vyhodnocení lomově-mechanických parametrů betonu po vystavení vysokým teplotám." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2018. http://www.nusl.cz/ntk/nusl-371838.

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The diploma thesis is focused on the evaluation of mechanical fracture parameters of concrete after exposure to high temperatures. In the introductory theoretical part general principles of fracture mechanics with the concentration on a linear elastic fracture mechanics and non-linear fracture models for the concrete are summarized. The meaning of the three-point bending fracture test used for determination of fracture parameters is also explained. Further the influence of high temperatures on the partial components of concrete and general modeling of temperature loading is described. The practical part is concerned with the evaluation of fire experiments on the concrete panels including numerical simulations using GiD and ATENA software. The evaluation of data obtained from the three-point bending test carried out on specimens with initial stress concentrator taken from concrete panels is a main part of the diploma thesis. The values of modulus of elasticity, effective fracture toughness, work of fracture and fracture energy are determined from the measured F–d and F–CMOD diagrams after their proper corrections in the GTDiPS application. The evaluation of the selected mechanical fracture parameters was performed by StiCrack software using effective crack model and work of fracture method and DKFM_BUT software using the double-K fracture model. Finally, the attention is paid to the analysis of the obtained data.
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29

Baietti, Giulia <1991&gt. "Mode-I fracture parameters of quasi-brittle materials: direct evaluation using DIC and relationship with Mode-II interfacial parameters." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amsdottorato.unibo.it/9788/1/baietti_giulia_tesi.pdf.

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The objective of this thesis is the investigation of the Mode-I fracture mechanics parameters of quasi-brittle materials to shed light onto the influence of the width and size of the specimen on the fracture response of notched beams. To further the knowledge on the fracture process, 3D digital image correlation (DIC) was employed. A new method is proposed to determine experimentally the critical value of the crack opening, which is then used to determine the size of the fracture process zone (FPZ). In addition, the Mode-I fracture mechanics parameters are compared with the Mode-II interfacial properties of composites materials that feature as matrices the quasi-brittle materials studied in Mode-I conditions. To investigate the Mode II fracture parameters, single-lap direct shear tests are performed. Notched concrete beams with six cross-sections has been tested using a three-point bending (TPB) test set-up (Mode-I fracture mechanics). Two depths and three widths of the beam are considered. In addition to concrete beams, alkali-activated mortar beams (AAMs) that differ by the type and size of the aggregates have been tested using the same TPB set-up. Two dimensions of AAMs are considered. The load-deflection response obtained from DIC is compared with the load-deflection response obtained from the readings of two linear variable displacement transformers (LVDT). Load responses, peak loads, strain profiles along the ligament from DIC, fracture energy and failure modes of TPB tests are discussed. The Mode-II problem is investigated by testing steel reinforced grout (SRG) composites bonded to masonry and concrete elements under single-lap direct shear tests. Two types of anchorage systems are proposed for SRG reinforced masonry and concrete element to study their effectiveness. An indirect method is proposed to find the interfacial properties, compare them with the Mode-I fracture properties of the matrix and to model the effect of the anchorage.
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30

Dubravec, Kristián. "Elastoplastická analýza napětí a deformace a stanovení lomových parametrů při tahovém namáhání těles s koncentrátory napětí." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2021. http://www.nusl.cz/ntk/nusl-443729.

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The aim of this thesis is the construction of a diagram of fracture strain for high strength steel OCHN3MFA and its application for the estimation of fracture toughness of this material. The first part of the thesis contains the necessary theoretical framework for numerical modelling of tensile tests of various specimens - smooth specimen, specimen with a notch and specimen with a circumferential crack, it describes the influence of triaxiality on the fracture of bodies and the possibilities of construction of the diagram of fracture strain. Subsequently, a numerical model of these specimens is created using the finite element method (FEM). A non-linear, elastoplastic calculation is performed. Fracture is identified by means of comparing the true stress versus the strain obtained from tests with the finite element analysis results. Stress–strain states of specimens at the moment of fracture are obtained from a numerical model. A diagram of fracture strain is constructed, and it is used to estimate the fracture toughness of a cracked body. Finally, a local approach, which uses the diagram of fracture strain, and a classical approach of fracture mechanics, especially the stress intensity factor, are compared.
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31

Michniak, Radomír. "Možnosti využití rozptýlené výztuže pro konstrukční betony." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2013. http://www.nusl.cz/ntk/nusl-226092.

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The master's thesis is focused on polypropylene fibres, their properties, availability, pitfalls associated with the use in practice. In the experimental part are the results of testing specimens with dispersed reinforcement fibers in varying proportions and their comparison.
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32

Nadri, Dariush. "Joint non-linear inversion of amplitudes and travel times in a vertical transversely isotropic medium using compressional and converted shear waves." Thesis, Curtin University, 2008. http://hdl.handle.net/20.500.11937/1810.

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Massive shales and fractures are the main cause of seismic anisotropy in the upper-most part of the crust, caused either by sedimentary or tectonic processes. Neglecting the effect of seismic anisotropy in seismic processing algorithms may incorrectly image the seismic reflectors. This will also influence the quantitative amplitude analysis such as the acoustic or elastic impedance inversion and amplitude versus offsets analysis. Therefore it is important to obtain anisotropy parameters from seismic data. Conventional layer stripping inversion schemes and reflector based reflectivity inversion methods are solely dependent upon a specific reflector, without considering the effect of the other layers. This, on one hand, does not take the effect of transmission in reflectivity inversion into the account, and on the other hand, ignores the information from the waves travelling toward the lower layers. I provide a framework to integrate the information for each specific layer from all the rays which have travelled across this layer. To estimate anisotropy parameters I have implemented unconstrained minimization algorithms such as nonlinear conjugate gradients and variable metric methods, I also provide a nonlinear least square method, based on the Levenberg-Marquardt algorithm. In a stack of horizontal transversely isotropic layers with vertical axis of symmetry, where the layer properties are laterally invariant, we provide two different inversion schemes; traveltime and waveform inversion.Both inversion schemes utilize compressional and joint compressional and converted shear waves. A new exact traveltime equation has been formulated for a dipping transversely isotropic system of layers. These traveltimes are also parametrized by the ray parameters for each ray element. I use the Newton method of minimization to estimate the ray parameter using a random prior model from a uniform distribution. Numerical results show that with the assumption of weak anisotropy, Thomsen’s anisotropy parameters can be estimated with a high accuracy. The inversion algorithms have been implemented as a software package in a C++ object oriented environment.
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33

Yi, Jangho. "Effect of Microstructural Parameters on Mechanical Properties and Fracture in α+β Titanium Alloy." Doctoral thesis, Kyoto University, 2019. http://hdl.handle.net/2433/244547.

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京都大学
0048
新制・課程博士
博士(工学)
甲第22066号
工博第4647号
新制||工||1725(附属図書館)
京都大学大学院工学研究科材料工学専攻
(主査)教授 辻 伸泰, 教授 安田 秀幸, 教授 宇田 哲也
学位規則第4条第1項該当
Doctor of Philosophy (Engineering)
Kyoto University
DFAM
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34

Botros, Farag Elia Farag. "On upscaling groundwater flow and transport parameters in porous and fractured media." abstract and full text PDF (free order & download UNR users only), 2007. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3275828.

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35

Young, Catherine Mary. "Do In-Line Dance, Progressively Loaded Squats and Foot Stomping Affect the Parameters of Fracture Risk in Postmenopausal Women?" Thesis, Griffith University, 2007. http://hdl.handle.net/10072/366122.

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Introduction: The incidence of hip fracture is increasing and the associated costs to individuals and the community needs to be vigorously addressed. This study was a randomized controlled intervention designed to examine the effects of a simple-to-do, easy-to-implement exercise programme on the elements of hip fracture risk which are known to be amenable to exercise therapy. Methods: Forty-five volunteers were randomly assigned to one of three groups. All groups attended one line dance class per week. Two groups additionally performed progressively loaded squats five times a week. One group also performed four foot stomps twice daily five times per week. Hip fracture risk (HFR), broadband ultrasound attenuation (BUA), proximal femoral (PF) and lumbar spine (LS) bone mineral density (BMD), squats number, and balance variables were measured. Results: There were no changes in HFR, BUA, PF or LS BMD, however, a strong positive stomps compliance effect was noted for BUA (r = 0.73, p = 0.003) and for PF BMD (r = 0.79, p = 0.002). Squats number increased in all participants, especially in those performing all three activities (p = 0.001). Single Leg Stance (SLS) times increased (p < 0.01), and Timed Up and Go (TUG) times decreased (p < 0.01) in all participants who complied with the protocol of squatting and stomping. Forward and lateral step velocities did not change. Conclusions: Our novel intervention conferred positive benefits on the skeletons of independent living, postmenopausal women. Other indices of fall and fracture risk, including muscle strength and balance, improved in all participants suggesting a beneficial effect of line dancing on these factors.
Thesis (Masters)
Master of Philosophy (MPhil)
School of Physiotherapy and Exercise Science
Faculty of Health
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36

Anjos, Ana Alexandra da Cunha Pereira. "" Objective Assessment of Acupuncture Effects By Microcirculation-Related Parameters in Patients With Proximal Femur Fracture "." Master's thesis, Instituto de Ciências Biomédicas Abel Salazar, 2011. http://hdl.handle.net/10216/57085.

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Anjos, Ana Alexandra da Cunha Pereira. "" Objective Assessment of Acupuncture Effects By Microcirculation-Related Parameters in Patients With Proximal Femur Fracture "." Dissertação, Instituto de Ciências Biomédicas Abel Salazar, 2011. http://hdl.handle.net/10216/57085.

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38

Aksu, Engin. "The Effect Of Austempering Parameters On Impact And Fracture Toughness Of Din 35nicrmov12.5 Gun Barrel Steel." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12606240/index.pdf.

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In this study the effects of different austempering times and temperatures on impact toughness, hardness and fracture toughness properties of 35NiCrMoV12.5 gun barrel steel are investigated. 300 °
C, 325 °
C and 350 °
C were chosen as austempering temperatures. Isothermal holding times at these temperatures were chosen as 1 minute, 10 minutes, 1 hour and 10 hours. It was found that, 350 °
C being an exception, austempering temperature and impact toughness has an inverse relationship and impact toughness increases as isothermal holding time increases. However this behavior is valid until some point. Prolonged transformation times causes toughness to decrease. Hardness measurements revealed that, as isothermal holding time increases, hardness decreases. In order to compare the mechanical properties obtained by austempering with that of conventional cooling and tempering, 400 °
C was chosen as the tempering temperature and applied to both charpy impact and fracture toughness specimens. It was found that conventional cooling and tempering produced tougher structures. Size of the fracture toughness specimens might have caused an undesired situation such as incomplete transformation to bainite. Optical and scanning electron microscopy was used in order to analyze the microstructures obtained after each treatment. It was observed that the majority of the morphologies occurred is lower bainite. On the other hand, martensitic structures were observed almost at every temperature.
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39

Freeman, P. N. "A study of parameters influencing fracture development in longwall coalfaces with particular reference to powered support." Thesis, Cardiff University, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329635.

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40

AZEVEDO, CECILIA TOLEDO DE. "FRACTURE PARAMETERS ESTIMATION THROUGH THE ANALYSIS OF THE PRESSURE CURVE DURING FRACTURING OF HIGH PERMEABILITY FORMATION." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2011. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=34622@1.

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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
PROGRAMA DE EXCELENCIA ACADEMICA
Valkó e Oligney propuseram um modelo que estima a evolução da fratura utilizando uma interpretação direta da curva de pressão de fundo medida durante uma operação de fracpack. Os únicos dados de entrada necessários para a aplicação do modelo são os registros geralmente disponíveis durante e após a operação. Considerando uma fratura de geometria radial e utilizando equações simples de fluxo e de geomecânica, o modelo obtém raios de empacotamento a partir da inclinação positiva da curva de pressão de fundo nos períodos de tip screenout. Nesta dissertação o modelo de Valkó e Oligney é aprimorado com a inclusão e o ajuste das equações de estado para o crescimento da fratura e para o processo de filtração, respectivamente. O modelo é também estendido para outras geometrias bidimensionais de fratura, PKN e KGD. A aplicação do modelo foi realizada utilizando os registros de pressão de oito operações de fracpack. Os resultados obtidos são a curva de propagação da fratura, o crescimento da abertura, a eficiência ao longo do tempo e a distribuição final do agente de sustentação na fratura. Para a validação desses resultados foram utilizados dois simuladores comerciais com modelos tridimensionais. Os estudos de caso indicaram que os ajustes realizados aproximaram os resultados do modelo aos obtidos nos simuladores comerciais. Além disso, a aplicação dos modelos desenvolvidos para cada geometria de fratura e a comparação com os resultados dos simuladores comerciais, permitiu confirmar a tendência esperada que, durante uma operação de fracpack, a geometria da fratura se aproxima da radial.
Valkó and Oligney developed a model to estimate fracture evolution using a direct interpretation of the measured bottom hole pressure curve during a fracpack operation. The only input data needed to use the model are the usual records of the job, available during and after the operation. Considering radial fracture geometry and using simplified equations of flow and geomechanics, the model estimates a packing radius of the fracture using the slope of the increasing bottom hole pressure curve during the tip screenout period. In this work, Valkó and Oligney method is enhanced with the inclusion of state equations for the fracture growth and for the leakoff process in order to improve the model, but still maintaining minimum input data. The method is also extended to other two-dimensional fracture geometries, PKN and KGD. To apply the enhanced method, eight fracpack operation data were used. The results obtained are fracture propagation, width growth and fluid efficiency in time as well as the final proppant distribution in the fracture. To validate these results, this work used two commercial simulators with three-dimensional models. The case studies show that the modifications done to Valkó and Oligney method approximate the two-dimensional model results to the ones obtained using the commercial simulators with threedimensional models. Furthermore, the comparison between the application of the model for each fracture geometry and the commercial simulators results confirmed the expected tendency for the fracture geometry during a fracpack operation, which is a radial fracture.
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41

Kay, Norman R. "A combined experimental and analytical approach for interface fracture parameters between dissimilar materials in electronic packages." Diss., The University of Arizona, 2003. http://hdl.handle.net/10150/289886.

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Failure of materials and interfaces are commonly linked to the fracture parameters such as the stress intensity factors and the energy release rate. However, there exists no experimental procedure for the direct measurement of these fracture parameters. This dissertation reports on the development of a new technique to obtain these parameters by testing specimens created from post-production electronic packages. The results from the experimental testing are then used as the input for an analytical model which computes the desired parameters. The specimens are thin strips of post production electronic packages. A crack is introduced along the interface in the specimen. Loading is applied to the specimen using the bend fixture inside the chamber of a scanning electron microscope, and images are captured following each load step. Digital image analysis on these images provides the displacement field around the crack tip to be used as boundary conditions in the analytical model. A hybrid formulation is developed utilizing the exact solution for the stress and displacement fields based on the eigenfunction expansion method under general loading. The region has two dissimilar elastic or viscoelastic material wedges with perfect bonding, and is not limited to a particular geometric configuration. The solution method is based on the principle of virtual work in conjunction with the use of Laplace transformation to eliminate time dependency. The strength of the singularity is obtained in the time space without resorting to approximate Laplace inversion techniques. However, the intensification of the stress components is obtained by employing an approximate inversion technique. One of the main contributions of this dissertation is the development of multiple techniques for the creation of test specimens from electronic packages. These methods involve different procedures of encapsulation for sectioning and techniques for the introduction of the crack to the interface. A second development is the technique of testing using image capture in conjunction with digital image correlation to find localized displacements. The third contribution from this work is the development of an analytical model to accurately model the region near the junction of two dissimilar viscoelastic materials.
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42

Nadri, Dariush. "Joint non-linear inversion of amplitudes and travel times in a vertical transversely isotropic medium using compressional and converted shear waves." Curtin University of Technology, Department of Exploration Geophysics, 2008. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=17631.

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Massive shales and fractures are the main cause of seismic anisotropy in the upper-most part of the crust, caused either by sedimentary or tectonic processes. Neglecting the effect of seismic anisotropy in seismic processing algorithms may incorrectly image the seismic reflectors. This will also influence the quantitative amplitude analysis such as the acoustic or elastic impedance inversion and amplitude versus offsets analysis. Therefore it is important to obtain anisotropy parameters from seismic data. Conventional layer stripping inversion schemes and reflector based reflectivity inversion methods are solely dependent upon a specific reflector, without considering the effect of the other layers. This, on one hand, does not take the effect of transmission in reflectivity inversion into the account, and on the other hand, ignores the information from the waves travelling toward the lower layers. I provide a framework to integrate the information for each specific layer from all the rays which have travelled across this layer. To estimate anisotropy parameters I have implemented unconstrained minimization algorithms such as nonlinear conjugate gradients and variable metric methods, I also provide a nonlinear least square method, based on the Levenberg-Marquardt algorithm. In a stack of horizontal transversely isotropic layers with vertical axis of symmetry, where the layer properties are laterally invariant, we provide two different inversion schemes; traveltime and waveform inversion.
Both inversion schemes utilize compressional and joint compressional and converted shear waves. A new exact traveltime equation has been formulated for a dipping transversely isotropic system of layers. These traveltimes are also parametrized by the ray parameters for each ray element. I use the Newton method of minimization to estimate the ray parameter using a random prior model from a uniform distribution. Numerical results show that with the assumption of weak anisotropy, Thomsen’s anisotropy parameters can be estimated with a high accuracy. The inversion algorithms have been implemented as a software package in a C++ object oriented environment.
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43

Milenko, Perović. "Uticaj parametara zavarivanja trenjem - miješanjem na otpornost prema lomu suočenog spoja legure aluminijuma visoke čvrstoće." Phd thesis, Univerzitet u Novom Sadu, Fakultet tehničkih nauka u Novom Sadu, 2018. https://www.cris.uns.ac.rs/record.jsf?recordId=107429&source=NDLTD&language=en.

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U disertaciji je predstavljen postupak spajanja topljenjem nezavarljive legure aluminijuma EW AN 7049A u stanju T 652 postupkom zavarivanja trenjem -miješanjem. Korišćenjem pet različitih tipova alata za zavarivanje, varijacijom brzine zavarivanja i broja obrtaja, zavareni spoj dostiže efikasnost od 70% do 80 % zatezne čvrstoće osnovnog materijala. Karakterizacija zavarenog spoja izvedena je standardnim metodama za eksperimentalno određivanje energije udara i udarne žilavosti na Charpy epruvetama, a ispitivanja mehanike loma zavarenih spojeva savijanjem u tri tačke SENB epruveta (ASTM E 1820), poprečno na pravac zavarivanja u zoni najviše pogođenom termomehaničkim uticajem alata.Kriterijumima elasto-plastične mehanike loma ( CTOD-otvaranje vrha prsline i J-integrala) utvrđena je veća otpornost prema širenju prsline u različitim mjestima zavarenog spoja (centru, strani napredovanja i na povratnoj strani metala šava) nego u osnovnom materijalu.
The thesis presents the procedure of joining by melting of unweldable alloy of Al EW AN 7049A of status T 652 by the procedure of friction-stir welding. By using five various types of tools for welding, variation of welding velocity and number of revolutions, the welded joint shall reach the efficiency of 70% -80% of tensile strenght of basic material. Characterization of welded joint was made by standard methods for experimental determination of impact energy and impact toughness on Charpy tubes, and breakage mechanical properties by bending in three points of SENB tubes (ASTM E 1820), transversely to direction of welding in the zone of highly affected thermo mechanical impact of tool. Criteria of elastoplastic mechanics of the fracture (CTOD crack opening displacement and J-integral) determined bigger resistivity to cracking at various locations of welded joint (center, side of advancing and on retreating side of the seam metal) than on the basic material.
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Taskonak, Burak. "The effects of residual stress, viscoelastic and thermodynamic parameters on apparent fracture toughness of dental bilayer ceramic composites." [Gainesville, Fla.] : University of Florida, 2004. http://purl.fcla.edu/fcla/etd/UFE0006425.

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Guo, Xiaofei [Verfasser]. "Influences of Microstructure, Alloying Elements and Forming Parameters on Delayed Fracture in TRIP/TWIP-Aided Austenitic Steels / Xiaofei Guo." Aachen : Shaker, 2012. http://d-nb.info/1066197296/34.

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46

Melin, Hanna. "Controlling parameters for normal and shear behaviour of rock fractures-a study of direct shear test data from SKB." Thesis, KTH, Jord- och bergmekanik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-93976.

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The deep mining and civil engineering industry need to perform rock stability analyses during excavation projects. The stability is mainly controlled by the shear strength of the rock fractures, which are the weakest point of the rock mass. In turn, the shear strength is governed by the mechanical properties of the fractures. It is both time and cost demanding to determine the properties of the rock fractures in laboratory. Also, the interpretation of the results requires a deep understanding of the normal and shear behaviour of rock fractures. This study aims to investigate if it is possible to determine the peak shear strength of rock fractures by merely estimating fracture parameters during field mapping and core logging. SKB supplied test results on drilled bore cores from site investigations in Forsmark and Laxemar for deep nuclear waste deposits. SKB generated data of high quality and in large quantity, which made it very valuable for the purpose of the study. The study begins with a literature review and an interaction matrix, clarifying the relationships between mechanical properties and affecting parameters of rock fractures. The predicted relationships of the parameters are then tested in an analysis based on the compiled data from SKB. The results show that the peak friction angle, the residual friction angle and the dilation angle are possible to approximate for open granite fractures in deep mining projects. Further on, the study proposes that the joint matching coefficient is included in the field mapping and core logging since it has a strong influence on the mechanical behaviour of the fracture, notably the normal and shear stiffness. Finally, the study questions estimations of JRC on small samples.
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47

Holušová, Táňa. "Analýza napjatosti a porušení ve zkušebních tělesech používaných pro určování lomově-mechanických parametrů kvazikřehkých materiálů." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2012. http://www.nusl.cz/ntk/nusl-225575.

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The thesis is focused on a test on determination of the fracture-mechanical parameters of quasi-brittle materials, especially concrete. What is referred to as the wedge-splitting test is considered, for which a variety of shapes of notched specimen can be used. This work is exclusively focused on the cylinder-shaped specimen of diameter 150 mm and breadth of 100 mm. The test is performed virtually using Atena 2D FEM software. Progress of failure is observed during loading of the specimen for various notch lengths. The amount of energy released for the development the failure outside of the tested cross-sectional area (weakened by the notch) is quantified and the size of the fracture process zone is investigated. The described analysis is performed for several material sets witch differ in cohesive properties of the quasi-brittle material expressed via the so-called characteristic length. Suitable proportions of the test specimen are sought, in order to avoid the failure and thus also the energy dissipation outside of the specimen ligament area during the experimental tests, which shall lead to more accurate estimates of fracture-mechanical parameters of the tested material.
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48

Lombard, Hannalie. "Optimized fatigue and fracture performance of friction stir welded aluminium plate : a study of the inter-relationship between process parameters, TMAZ, microstructure, defect population and performance." Thesis, University of Plymouth, 2007. http://hdl.handle.net/10026.1/2389.

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Friction stir welding (FSW) is an exciting new solid-state welding process with the potential to advantageously impact many fabrication industries. Current take-up of the process by industry is hindered by lack of knowledge of suitable welding parameters for any particular alloy and sheet thickness. The FSW process parameters are usually chosen empirically and their success is evaluated via simple mechanical property testing. There are severe drawbacks with such methods of determining manufacturing conditions. These include indirect relationships between tensile and fatigue properties, particularly for welds, and a high probability of totally missing real optimized conditions. This research is therefore undertaken as a first step in providing information that will assist manufacturing industry to make sound decisions with respect to selecting FSW parameters for weldable structural alloys. Some of the key issues driving material selection for manufacturing are weld quality in terms of defects, fatigue strength and crack growth, and fracture toughness. Currently a very limited amount of data exists regarding these mechanical properties of FSW welds, and even less information exists regarding process parameter optimization. This is due to the mechanical microstructural complexity of the process and the relatively large number of process parameters (feed, speed, force and temperature) that could influence weld properties. In order to advance predictive understanding and modeling for FS welds, it is necessary to develop force and energy based models that reflect the underlying nature of the thermo-mechanical processes that the material experiences during welding. This project aims at determining the influence and effect of Friction Stir Welding process control parameters on the microstructure of the thermo-mechanically affected zone, the defect population in the weld nugget, hardness, residual stresses, tensile and fatigue performance of 6 mm plate of 5083-H321 aluminium alloy, which is known to be susceptible to planar defect formation. Welds were made with a variety of process parameters (that is feed rate and rotational speed) to create different rates of heat input. Forces on the FSW tool (horizontal and vertical), torque and tool temperature were measured continuously during welding from an instrumented FSW tool. Detailed information on fatigue performance, residual stress states, microstructure, defect occurrence, energy input and weld process conditions, were investigated using regression models and contour maps which offer a unique opportunity to gain fundamental insight into the process-structure-property relationships for FS welds. Weld residual strains have been extensively measured using synchrotron X-ray diffraction strain scanning to relate peak residual stresses and the widths of the peak profiles, taken from a single line scan from the mid depth of the FS welds, with the weld process conditions and energy input into the welds. Several residual stress maps were also investigated. The optical and scanning electron microscope were used to determine the type of intrinsic defects present in the FSW fatigue and tensile specimens. Vickers hardness measurements were taken from the mid depth of the welds and were compared with the weld input parameters. The main contribution of this thesis is as follow: (i) the relationship between input parameters and process parameters; (ii) the relationship between input weld parameters (that is feed rate and rotational speed) and process parameters (that is vertical downwards force Fz, tool temperature, tool torque and the force footprint data), energy input and tensile strength, fatigue life and residual stresses to obtain regions of optimum weld conditions; (iii) identification of the defects present in FSW, their relationship with process parameters and their effect on tensile strength and fatigue life; and (iv) the usefulness of the real time process parameter monitoring automated instrumented FSW tool to predict the mechanical properties of the welds.
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LE, GIA VINH. "Extraction de parametres de texture d'images de croissance cristalline dendritique." Université Joseph Fourier (Grenoble), 1996. http://www.theses.fr/1996GRE10181.

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La croissance cristalline de cucl#2, 2h#2o par evaporation en presence d'impuretes de type biologique donne naissance a une structure dendritique quasi-bidimensionnelle dont l'image est caracteristique des impuretes introduites. Cette methode est appliquee dans les domaines du vivant (agro-alimentaire et sante) sous le nom de thesigraphie. L'etude a pour objectif, apres un bilan de l'etat de l'art de methodes d'analyse visuelle, de definir une methodologie de caracterisation de ces images par les techniques de traitement d'image et de classification. Apres un recensement des caracteristiques visuelles de ces images, les choix d'acquisition, de pretraitement et d'amelioration des images sont presentes. Les techniques d'analyse retenues sont la segmentation (methodes de seuillage, de squeletisation) et l'analyse de texture (y compris la dimension fractale). Les attributs issus de ces techniques sont utilises en entree de classifieur. La classification supervisee a ete utilisee et elle permet avec succes de classifier les etats de degradation biologique d'un produit agro-alimentaire
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Santafe, Iribarren Berta. "Progressive collapse simulation of reinforced concrete structures: influence of design and material parameters and investigation of the strain rate effects." Doctoral thesis, Universite Libre de Bruxelles, 2011. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209912.

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This doctoral research work focuses on the simulation of progressive collapse of reinforced concrete structures. It aims at contributing to the ‘alternate load path’ design approach suggested by the General Services Administration (GSA) and the Department of Defense (DoD) of the United States, by providing a detailed yet flexible numerical modelling tool.

The finite element formulation adopted here is based on a multilevel approach where the response at the structural level is naturally deduced from the behaviour of the constituents (concrete and steel) at the material level. One-dimensional nonlinear constitutive laws are used to model the material response of concrete and steel. These constitutive equations are introduced in a layered beam approach, where the cross-sections of the structural members are discretised through a finite number of layers. This modelling strategy allows deriving physically motivated relationships between generalised stresses and strains at the sectional level. Additionally, a gradual sectional strength degradation can be obtained as a consequence of the progressive failure of the constitutive layers. This means that complex nonlinear sectional responses exhibiting softening can be obtained even for simplified one dimensional constitutive laws for the constituents.

This numerical formulation is used in dynamic progressive collapse simulations to study the structural response of a multi-storey planar frame subject to a sudden column loss. The versatility of the proposed methodology allows assessing the influence of the main material and design parameters in the structural failure. Furthermore, the effect of particular modelling options of the progressive collapse simulation technique, such as the column removal time or the strategy adopted for the structural verification, can be evaluated.

The potential strain rate effects on the structural response of reinforced concrete frames are also investigated. To this end, a strain rate dependent material formulation is developed, where the rate effects are introduced in both the concrete and steel constitutive response. These effects are incorporated at the structural level through the multilayered beam approach. In order to assess the degree of rate dependence in progressive collapse, the results of rate dependent simulations are presented and compared to those obtained via the rate independent approach. The influence of certain parameters on the rate dependent structural failure is also studied.

The differences obtained in terms of progressive failure degree for the considered parametric variations and modelling options are analysed and discussed. The parameters observed to have a major influence on the structural response in a progressive collapse scenario are the ductility of the steel bars, the degree of symmetry and/or continuity of the reinforcement and the column removal time. The results also depend on the strategy considered (GSA vs DoD). The strain rate effects are confirmed to play a significant role in the failure pattern. Based on these observations, general recommendations for the design of progressive collapse resisting structures are finally derived.

L’effondrement progressif est un sujet de recherche qui a connu un grand développement suite aux événements désastreux qui se sont produits au cours des dernières décennies. Ce phénomène est déclenché par la défaillance soudaine d’un nombre réduit d’éléments porteurs de la structure, qui provoque une propagation en cascade de l’endommagement d’élément en élément jusqu’à affecter une partie importante, voire la totalité de l’ouvrage. Le résultat est donc disproportionné par rapport à la cause. La plupart des codes de construction ont inclus des prescriptions pour le dimensionnement des structures face aux actions accidentelles. Malheureusement, ces procédures se limitent à fournir des ‘règles de bonne pratique’, ou proposent des calculs simplifiés se caractérisant par un manque de détail pour permettre leur mise en oeuvre.

Cette thèse de doctorat intitulée Simulation de l’Effondrement Progressif des Structures en Béton Armé: Influence des Paramètres Materiaux et de Dimensionnement et Investigation des Effets de Vitesse a pour but de contribuer à la simulation numérique de l’effondrement progressif des structures en béton armé. Une formulation aux éléments finis basée sur une approche multi-échelles a été développée, où la réponse à l’échelle structurale est déduite à partir de la réponse au niveau matériel des constituants (le béton et l’acier). Les sections des éléments structuraux sont divisées en un nombre fini de couches pour lesquelles des lois constitutives unidimensionnelles sont postulées. Cet outil permet une dégradation graduelle de la résistance des sections en béton armé suite à la rupture progressive des couches. Des comportements complexes au niveau des points de Gauss peuvent être ainsi obtenus, et cela même à partir de lois unidimensionnelles pour les constituants.

Cette formulation est utilisée pour la simulation de l’effondrement progressif d’ossatures 2D, avec prise en compte des effets dynamiques. La versatilité de la présente stratégie numérique permet d’analyser l’influence de différents paramètres matériaux et de dimensionnement, ainsi que d’autres paramètres de modélisation, sur la réponse structurale face à la disparition soudaine d’une colonne.

Les effets de la vitesse de déformation sur le comportement des matériaux constituants est aussi un sujet d’attention dans ce travail de recherche. Des lois constitutives prenant en compte ces effets sont postulées et incorporées au niveau structural grâce à l’approche multi-couches. Le but est d’étudier l’influence des effets de la vitesse de chargement sur la réponse structurale face à la disparition d’un élément porteur. Les resultats obtenus à l’aide de cette approche avec effets de vitesse sont comparés à ceux obtenus avec des lois indépendantes de la vitesse.

Les différences dans la réponse à la disparition d’une colonne sont analysées pour les variations paramétriques étudiées. Les paramètres ayant une influence importante sont notamment: la ductilité des matériaux constituants et la disposition et/ou la symétrie des armatures. Les effets de vitesse sont également significatifs. Sur base de ces résultats, des recommandations sont proposées pour le dimensionnement et/ou l’analyse des structures face à l’effondrement progressif.


Doctorat en Sciences de l'ingénieur
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