Cracking is one of the most severe distress modes of asphaltpavements. Thus characterising the fracture resistance properties of asphaltmixtures is the key issue for improving the performance relatedmixture design. The present master thesis project addresses the implementationof the theoretical framework, which is used to characterise thefracture resistance of mixtures based on the SuperPave indirect tensiletest (IDT). An open source Matlab-based software for analysing resilientmodulus, Poisson’s ratio, creep parameters and fracture resistance parametershas been developed. The software analyses the the IDT results, toestimate mixture’s fracture resistance based on hot mix asphalt FractureMechanics. Predictions form the field specimens concerning the fractureresistance obtained from IDT are compared with observed field performance.

Road administrators have to make decisions regarding the maintenance and rehabilitation of many existing jointed Portland Cement Concrete (PCC) pavements in the road network. Since these pavements are in general expensive to rehabilitate, agencies often opt for overlaying the deteriorated PCC pavement with Hot Mix Asphalt (HMA), resulting in a composite pavement. Unfortunately, the tensile stresses and strains at the bottom of the overlay developed from the movement of the joints, which are caused by the traffic and the changes in temperature, will create cracks on the surface known as reflective cracking. Reflective cracking can reduce the life of a pavement by allowing water or other particles to get into the underlying layers, which causes the pavement structure to lose strength. To improve the performance of the composite pavement, road agencies have studied mitigations techniques to delay the initiation and propagation of those cracks reflected from the PCC joints and cracks. Traditionally, these studies have relied only on laboratory testing or nondestructive tests. This dissertation expands the traditional approach by adding full-scale Accelerate Pavement Testing (APT) to a laboratory effort to investigate enhanced asphalt overlays that delay the initiation and propagation of cracks reflected from the PCC joints. The study was organized into three complementary experiments. The first experiment included the first reflective cracking study of hot-mix asphalt (HMA) overlays over jointed Portland cement concrete pavements (PCCP) conducted at the Virginia APT facility. A Heavy Vehicle Simulator (HVS) was used to compare the reflective cracking performance of a Stone Matrix Asphalt (SMA) control mix with a modified mix with a synthetic fiber. The discussion includes the characterization of the asphalt mixes, the pavement structure, construction layout, the equipment used, the instrumentation installed, and lessons learned. Results showed that the fiber-modified mix had a higher resistance to fracture, which increases the pavement life by approximately 50%. The second experiment compared the cracking resistance of the same control and modified mixes in the laboratory. Four cracking resistance tests were performed on each mix. These four tests are: (1) Indirect Tensile Asphalt Cracking Test (IDEAL-CT), which measures the Cracking Test index (CTindex); (2) Semicircular Bend Test-Illinois (SCB-IL), which measures the critical strain energy release rate (Jc); (3) Semicircular Bend-Louisiana Transportation Research Center (SCB-LTRC), which measures the Flexibility Index (FI); and (4) Overlay Test (OT), which measures the Cracking Propagation Rate (CPR). The results from the four tests showed that the fiber-modified mix had a better resistance to cracking, confirming the APT test results. The laboratory assessment also suggested that the IDEAL-CT and SCB-IL test appear to be the most practical for implementation. The third phase evaluated the performance of mixes designed with a high content of Reclaimed Asphalt Pavement (RAP) and an enhanced asphalt-rubber extender, which comprises three primary components: plain soft bitumen, fine crumb rubber and an Activated Mineral Binder Stabilizer (AMBS). The experiment evaluated the fracture resistance of nine mixes designed with different rates of recycled asphalt pavement (RAP) and asphalt-rubber, compare them with a traditional mix, and propose an optimized mixture for use in overlays of concrete pavements. The mixes were designed with different rates of RAP (15, 30, 45%) and asphalt-rubber extender (0, 30, and 45%) following generally, the design requirements for an SMA mix in Virginia. The laboratory test recommended in the second experiment, IDEAL-CT and SCB-IL, were used to determine the fracture resistance of the mixes. The results showed that the addition of RAP decreases fracture resistance, but the asphalt-rubber extender improves it. A mix designed that replaced 30% of the binder with asphalt-rubber extender and 15% RAP had the highest resistance to fracture according to both. Also, as expected, all the mixed had a low susceptibility to rutting. / Doctor of Philosophy / Reflective cracking can reduce the life of a pavement by allowing water or other particles to get into the underlying layers, which causes the pavement structure to lose strength. To improve the performance of the composite pavement, road agencies have studied mitigations techniques that will delay the initiation and propagation of those cracks reflected from the PCC joints. Traditionally, these studies rely only on laboratory testing or nondestructive tests that will assist in the decision-making stage in a short time manner. This dissertation focusses on a reflective cracking study conducted through Accelerate Pavement Testing (APT) using a Heavy Vehicle Simulator (HVS) and laboratory testing. The first task used an HVS to evaluate reflective cracking of a Stone Matrix Asphalt (SMA) control mix and a modified mix with synthetic fiber. One lane was constructed with two layers of 1.5-inches of a control Stone Matrix Asphalt (SMA) mix and the second lane with an SMA mix modified with the synthetic fiber. Results from APT demonstrated that the modified SMA has a higher resistance to fracture which increases the pavement life by approximately 50%. The second task estimated the fracture resistance of the mixes studied in task one following the laboratory test: Indirect Tension Asphalt Cracking Test (IDEAL-CT), Texas Overlay Test (OT), Semi-Circular Bend-Louisiana Transportation Research Center (SCB-LTRC) and Semi-Circular Bend-Illinois (SCB-IL) to estimate the Cracking Test Index (CTindex), Cracking Propagation Rate (CPR), critical strain energy release rate (Jc) and Flexibility Index (FI), respectively. Results showed that the modified mix had a better resistance to cracking, confirming the APT test results. Specifically, CTindex results showed that the modified mix is more resistant than the control, with indices of 268.72 and 67.86. The estimated Jc indicated that less energy is required to initiate a crack for the control mix that achieved 0.48 kJ/m2 compared to the modified mix with synthetic fibers 0.54 kJ/m2. FI results for the control and fibers were 2.16 and 10.71, respectively. The calculated CPR showed that the control mix propagates a crack at a higher rate of 0.188 compared to the modified mix with a CPR of 0.152. The third phase evaluated the performance of mixes designed with a high content of Reclaimed Asphalt Pavement (RAP) and an enhanced asphalt-rubber extender, which comprises three primary components: plain soft bitumen, fine crumb rubber and an Activated Mineral Binder Stabilizer (AMBS). The experiment evaluated the fracture resistance of nine mixes designed with different rates of recycled asphalt pavement (RAP) and asphalt-rubber, compare them with a traditional mix, and propose an optimized mixture for use in overlays of concrete pavements. The mixes were designed with different rates of RAP (15, 30, 45%) and asphalt-rubber extender (0, 30, and 45%) following generally, the design requirements for an SMA mix in Virginia. The laboratory test recommended in the second experiment, IDEAL-CT and SCB-IL, were used to determine the fracture resistance of the mixes. The results showed that the addition of RAP decreases fracture resistance, but the asphalt-rubber extender improves it. A mix designed that replaced 30% of the binder with asphalt-rubber extender and 15% RAP had the highest resistance to fracture according to both. Also, as expected, all the mixed had a low susceptibility to rutting.

As hydrogel products are manufactured and used for applications ranging from biomedical to agricultural, it is useful to characterize their behavior and interaction with other materials. This thesis investigates the adhesion between two different solvated semi-interpenetrating polymer network (S-IPN) silicone hydrogels and a cyclo-olefin (COP) polymer through experimental, analytical, and numerical methods. Interfacial fracture data was collected through the application of the wedge test, a relatively simple test allowing for the measurement of fracture properties over time in environments of interest. In this case, the test was performed at discrete temperatures within range of 4Ë C to 80Ë C. Two COP adherends were bonded together by a layer of one of the S-IPN silicone hydrogels. Upon the insertion of a wedge between the two adherends, debonding at one of the two interfaces would initiate and propagate at a decreasing rate. Measurements were taken of the debond length over time and applied to develop crack propagation rate versus strain energy release rate (SERR) curves. The SERR values were determined through the application of an analytical model derived for the wedge test geometry and to take into account the effects of the hydrogel interlayer. The time-temperature superposition principle (TTSP) was applied to the crack propagation rate versus SERR curves by shifting the crack propagation rates with the Williams-Landel-Ferry (WLF) equation-based shift factors developed for the bulk behavior of each hydrogel. The application of TTSP broadened the SERR and crack propagation rate ranges and presented a large dependency of the adhesion of the system on the viscoelastic nature of the hydrogels. Power-law fits were applied to the master curves in order to determine parameters that could describe the adhesion of the system and be applied in the development of a finite element model representing the interfacial fracture that occurs for each system. The finite element models were used to validate the analytical model and represent the adhesion of the system such that it could be applied to future geometries of interest in which the S-IPN silicone hydrogels are adhered to the COP substrate. <i>[Files modified per J. Austin, July 9, 2013 Gmc]</i> / Master of Science

Wikipedia umschreibt die Topologieoptimierung als ein computerbasiertes Berechnungsverfahren, durch welches eine günstige Grundgestalt (Topologie) für Bauteile unter mechanischer Belastung ermittelt werden kann. Durch die Verwendung von 3D-Druck-Verfahren wird die Gestaltung der Komponenten revolutioniert, weil diese nicht mehr abhängig vom Fertigungsverfahren sind. Dabei werden auch optimale Gitterstrukturen innerhalb der Komponenten immer wichtiger. Diese neuen Herausforderungen können im Creo Umfeld mit ProTopCI (Hersteller CAESS, PTC Partner Advantage, Silver) elegant gelöst werden. Im Vortrag (mit Live-Demonstration) werden die neuen Möglichkeiten dieser innovativen Lösung beleuchtet: Modellerzeugung in Creo Simulate (FEM-Mode): - Verschiedene Lastfälle, - Kontakte, - Schraubenverbindungen, - CAD-Geometrie, - zu optimierende Bereiche, ... Technologische Randbedingungen zur Berücksichtigung des Fertigungsverfahren Innovatives Erzeugen/Optimieren der Gitterstrukturen Glätten, Exportieren der optimierten Geometrie

Multi-layered electronic packages increase in complexity with demands for functionality. Interfacial delamination remains a prominent failure mechanism due to mismatch of coefficient of thermal expansion (CTE). Numerous studies have investigated interfacial cracking in microelectronic packages using fracture mechanics, which requires knowledge of starter crack locations and crack propagation paths. Cohesive zone theory has been identified as an alternative method for modeling crack propagation and delamination without the need for a pre-existing crack. In a cohesive zone approach, traction forces between surfaces are related to the crack tip opening displacement and are governed by a traction-separation law. Unlike traditional fracture mechanics approaches, cohesive zone analyses can predict starter crack locations and directions or simulate complex geometries with more than one type of interface. In a cohesive zone model, cohesive zone elements are placed along material interfaces. Parameters that define cohesive zone behavior must be experimentally determined to be able to predict delamination propagation in a microelectronic package. The objective of this work is to study delamination propagation in a copper/mold compound interface through cohesive zone modeling. Mold compound and copper samples are fabricated, and such samples are used in experiments such as four-point bend test and double cantilever beam test to obtain the cohesive zone model parameters for a range of mode mixity. The developed cohesive zone elements are then placed in a small-outline integrated circuit package model at the interface between an epoxy mold compound and a copper lead frame. The package is simulated to go through thermal profiles associated with the fabrication of the package, and the potential locations for delamination are determined. Design guidelines are developed to reduce mold compound/copper lead frame interfacial delamination.

<p>Predmet ove doktorske disertacije je definisanje metoda i procedure<br />za procenu veka konstrukcije tornja postrojenja za istraživanje nafte<br />i gasa. Dati su rezultati eksperimentalnih istraživanja radi analize<br />otpornosti prema prslinama pri statičkom i pri promenljivom<br />opterećenju eksploatisanog i novog materijala konstrkcije tornja<br />postrojenja za istraživanje nafte i gasa.</p> / <p>The topic of this doctoral dissertation is definition methods and proceduries for an<br />analysis of an assessmen life of construction derrick plant for investigation oil<br />and gas. The results of experimental investigation performed for the analysis<br />of crack resistance under static and under variable loading eksploatacion<br />and new of materials of construction derrick plant for investigation oil and gas.</p>

L'Inconel 718 est un superalliage base nickel très utilisé pour produire les disques de turboréacteurs. Typiquement, une gamme de forgeage à chaud se compose de plusieurs étapes de déformation et de recuit. La présence des particules de seconde phase (particules de phase delta dans l'Inconel 718) permet en principe de limiter la croissance de grains pendant les étapes de recuit grâce au phénomène d'ancrage de Zener. Néanmoins, l'hétérogénéité microstructurale (distribution des particules, écrouissage, composition chimique) peut favoriser une croissance anormale des grains pendant le recuit. Ce phénomène est connu industriellement sous la terminologie d'"éclatement de grains". Les objectifs de la thèse étaient d'identifier les mécanismes responsables de l'éclatement des grains qui peut survenir durant les étapes de recuit sur les pièces forgées en Inconel 718, de les modéliser, et de simuler numériquement le phénomène. Les mécanismes physiques à l'origine du phénomène sont d'abord étudiés expérimentalement grâce à la caractérisation (par MEB et EBSD) des pièces forgées. L'influence des particules de seconde phase et de l'énergie stockée (estimée par des mesures de désorientations intragranulaires) est notamment étudiée. A partir des observations réalisées, une explication est proposée : le phénomène apparaît lorsque les forces motrices pour la migration des joints de grains dépassent la force de freinage de Zener ; ceci peut se produire lorsque la microstructure contient de l'énergie stockée, distribuée de manière hétérogène. Des essais de torsion à chaud sont mis en place pour reproduire, en laboratoire, le même phénomène, étudier la sensibilité aux paramètres thermomécaniques, et tester les hypothèses émises concernant les mécanismes. Les mécanismes ainsi identifiés comme responsables de l'éclatement de grains sont enfin simulés au moyen d'un modèle numérique en 2D. Le modèle numérique en champ complet est basé sur la méthode des éléments finis, et utilise le formalisme level-set pour décrire les joints de grains. La simulation de l'évolution microstructurale prend en compte à la fois les forces motrices des joints de grains liées à la capillarité et à l'énergie stockée, et l'interaction des joints de grains avec les particules de seconde phase. Ainsi, l'effet de la distribution de l'énergie stockée (estimée à partir de données expérimentales) a pu être étudié numériquement dans des microstructures avec particules. / Inconel 718 is a nickel base superalloy commonly used to manufacture the rotating disks of turbojet engines. Such disks are generally produced by hot forging, which involves a sequence of different deformation and annealing steps. The presence of second phase particles (delta phase in Inconel 718) is commonly exploited to limit grain growth during annealing via the Zener pinning phenomenon. Nonetheless, microstructure heterogeneity (with regards to second phase particles, hardening, texture and chemical composition) can lead to inhomogeneous grain growth during annealing. The objectives of this PhD work were to understand, model and simulate numerically the phenomenon of inhomogeneous grain growth that can occur in Inconel 718 turbine disks during the annealing steps of hot forging sequences. The physical mechanisms which may explain the occurrence of the phenomenon are investigated experimentally by performing SEM and EBSD analyses of Inconel 718 industrial pieces. The focus is placed on the influence of second phase particles and strain energy (estimated from intragranular misorientations) on the occurrence of the phenomenon. From those observations, it is inferred that the phenomenon occurs when the grain boundary driving forces overcome the Zener pinning forces; this is achieved when stored energy is present and heterogeneously distributed. Moreover, hot torsion tests are carried out to reproduce the phenomenon in laboratory, to evaluate its sensibility to thermomechanical parameters and to test the previously postulated mechanism. The validity of this mechanism is finally demonstrated by modelling numerically the phenomenon in 2D. The full field numerical model is based on a level set description of the grain boundaries in a finite element context. Microstructure evolution is simulated explicitly taking into account Zener pinning, capillarity and stored energy driven grain growth in a single framework. The effect of strain stored energy distributions (estimated from experimental data) in pinned microstructures is investigated focusing on the conditions leading to inhomogeneous grain growth.

Due to their ability to confer enhanced surface properties without compromising the properties of the substrate, coatings have become ubiquitous in heavy industrial applications for corrosion, wear, and thermal protection, among others. Kinetic Metallization (KM), a solid-state impact consolidation and coating process, is well-suited for depositing industrial coatings due to its versatility, low substrate heat input, and low cost. The ability of KM coatings to adhere to the substrate is determined by the quality of the interface. The purpose of this study is to develop a model to predict the interfacial quality of KM coatings using known coating and substrate properties. Of the various contributions to adhesion of KM coatings, research suggests that the thermodynamic Work of Adhesion (WAD) is the most fundamental. It is useful to define interfacial quality in terms of the critical strain energy release rate (GC) at which coating delamination occurs. Studies show that GC for a given interface is related to WAD. This study attempts to develop a theoretical model for calculating WAD and understand the relationship between GC and WAD. For a bimetallic interface between two transition metals, WAD can be theoretically calculated using known electronic and physical properties of each metal: the molar volume, V, the surface energy, γ, and the enthalpy of alloy formation, ΔHinterface; ΔHinterface is a function of the molar volume, V, the work function, φ, and the electron density at the boundary of the Wigner-Seitz cell, nWS.WAD for Ni-Cu and Ni-Ti interfaces were 3.51 J/m2 and 4.55 J/m2, respectively. A modified Four-point bend testing technique was used to experimentally measure GC for Ni-Cu and Ni-Ti specimens produced by KM. These tests yielded mean G­C values of 50.92 J/m2 and 132.68 J/m2 for Ni-Cu and Ni-Ti specimens, respectively. Plastic deformation and surface roughness are likely the main reasons for the large discrepancy between GC and WAD. At the 95% confidence level, the mean GC of the Ni-Ti interface is significantly higher than that of the Ni-Cu interface. Further testing is recommended to better understand the relationship between WAD and GC.

No description available.

Carbon fiber-reinforced silicon carbide matrix (C/SiC) composite is a ceramic matrixcomposite (CMC) that has considerable promise for use in high-temperature structuralapplications. In this thesis, systematic numerical studies including the prediction of elasticand thermal properties, analysis and optimization of stresses and simulation ofhigh-temperature oxidations are presented for the investigation of C/SiC composites.A strain energy method is firstly proposed for the prediction of the effective elastic constantsand coefficients of thermal expansion (CTEs) of 3D orthotropic composite materials. Thismethod derives the effective elastic tensors and CTEs by analyzing the relationship betweenthe strain energy of the microstructure and that of the homogenized equivalent model underspecific thermo-elastic boundary conditions. Different kinds of composites are tested tovalidate the model.Geometrical configurations of the representative volume cell (RVC) of 2-D woven and 3-Dbraided C/SiC composites are analyzed in details. The finite element models of 2-D wovenand 3-D braided C/SiC composites are then established and combined with the stain energymethod to evaluate the effective elastic constants and CTEs of these composites. Numericalresults obtained by the proposed model are then compared with the results measuredexperimentally.A global/local analysis strategy is developed for the determination of the detailed stresses inthe 2-D woven C/SiC composite structures. On the basis of the finite element analysis, theprocedure is carried out sequentially from the homogenized composite structure of themacro-scale (global model) to the parameterized detailed fiber tow model of the micro-scale(local model). The bridge between two scales is realized by mapping the global analysisresult as the boundary conditions of the local tow model. The stress results by global/localmethod are finally compared to those by conventional finite element analyses.Optimal design for minimizing thermal residual stress (TRS) in 1-D unidirectional C/SiCcomposites is studied. The finite element models of RVC of 1-D unidirectional C/SiCIIcomposites with multi-layer interfaces are generated and finite element analysis is realized todetermine the TRS distributions. An optimization scheme which combines a modifiedParticle Swarm Optimization (PSO) algorithm and the finite element analysis is used toreduce the TRS in the C/SiC composites by controlling the multi-layer interfaces thicknesses.A numerical model is finally developed to study the microstructure oxidation process and thedegradation of elastic properties of 2-D woven C/SiC composites exposed to air oxidizingenvironments at intermediate temperature (T<900°C). The oxidized RVC microstructure ismodeled based on the oxidation kinetics analysis. The strain energy method is then combinedwith the finite element model of oxidized RVC to predict the elastic properties of composites.The environmental parameters, i.e., temperature and pressure are studied to show theirinfluences upon the oxidation behavior of C/SiC composites.