Concrete dams located in northern regions are exposed to large seasonal temperature variations. These seasonal temperature variations have resulted in cracking in thin concrete dams. Continuous monitoring and evaluation of existing dams are important to increase the knowledge about massive concrete structures and to ensure dam safety.  The aim of this degree project is to increase the knowledge about how cracking occurs in concrete dams and how it affects the dam safety. This was achieved by simulating the development of cracks in a concrete arch dam exposed to seasonal temperature variations using finite element analysis (FEA). The accuracy of the model was evaluated by comparing the results with measurements from a Swedish concrete arch dam. Finally, effect of cracks and temperature on the dam safety was investigated.  FEA was used to predict the crack pattern and displacements in the arch dam. The analyses were performed both with linear elastic and nonlinear material behavior. Two models were analyzed, in one model the dam was considered to be a homogeneous arch, the other model included contraction joints. The cracking was simulated using temperature envelopes from the location of the Swedish arch dam. To evaluate the displacements in the arch, further analyses were carried out, where the cracked arch dam was exposed to the actual temperature variations at the location. The results were compared to the crack pattern and measurements of displacements of the Swedish arch dam. To investigate the effects from the cracking on the safety of the dam, a progressive failure analyses performed.  The results show that the downstream face of the arch cracked under hydrostatic pressure. The cracks propagated further during winter when the temperature load was applied. The resulting crack pattern corresponded well with the survey of the cracks from the Swedish arch dam. The FE-models with nonlinear material developed a horizontal plastic hinge due to excessive cracking in a region halfway down from the crest. The plastic hinge affected the shape of the deflected arch. The magnitude of the displacements and the shape of the deflected arch was captured with the nonlinear models. A safety factor of 3 for internal structural failure in the arch was found in the failure analyses. The safety factor of the arch only decreased slightly due to the cracking. During a cold winter, the safety factor decreased to 2.5. / Betongdammar belägna i nordliga klimat blir utsatta för stora säsongsburna temperaturvariationer. Dessa temperaturvariationer har orsakat sprickbildning i tunna betongdammar. Kontinuerlig övervakning och utvärdering av befintliga dammar är viktigt för att öka kunskapen om massiva betongkonstruktioner och för att säkerställa dammsäkerheten.  Syftet med det här examensarbetet är att öka kunskapen om hur sprickor uppstår i valvdammar samt hur de påverkar anläggningens säkerhet. Målet är att med finit elementanalys (FEA) analysera uppsprickningen av betongen i en valvdamm som påverkas av säsongsburna temperaturvariationer. Tillförlitligheten i modellen utvärderas genom att jämföra med mätningar från en svensk valvdamm av liknande dimensioner. Slutligen utvärderas hur dammens säkerhet påverkas av sprickbildningen.  FE-analys användes för att förutsäga sprickmönstret och förskjutningarna i valvdammen. Analyserna utfördes både med linjärelastiskt och icke-linjärt materialbeteende. Två modeller användes i analysen, i ena modellen betraktades dammen som homogen och i den andra inkluderades gjutfogar. Sprickmönstret simulerades med temperaturcykler baserade på extremtemperaturer tagna intill den svenska valvdammen. För att utvärdera förskjutningarna i dammen gjordes vidare analyser där den spruckna dammen utsattes för temperaturvariationer uppmätta från samma plasts. Resultaten från analysen jämfördes med mätningar av förskjutningar och kartering av sprickor från den svenska valvdammen. För att undersöka hur säkerheten påverkades av sprickbildningen utfördes progressiv brottanalys.  Resultaten visar att dammen spricker på nedströmssidan när den utsätts för vattentryck. Sprickorna fortplantas under vintern när temperaturlasten appliceras. Sprickmönstret stämmer överens med kartering av den verkliga dammen. FE-modellerna med icke-linjärt materialbeteende utvecklade en plastisk led längs horisontella sprickor halvvägs ner från krönet. Den plastiska leden påverkade dammens utböjda form. Förskjutningarna och dammens utböjda form i de ickelinjära modellerna stämmer väl överens med de uppmätta förskjutningarna. Vid brottanalysen var säkerhetsfaktorn mot materialbrott i dammen 3. Säkerhetsfaktorn minskade något till följd av sprickorna. Under en kall vinter sjönk säkerhetsfaktorn till 2,5.

<p>Meteorites fallen from the sky and surface particles of the moon gathered by lunar space missions, have distinct microstructure and properties that can provide unique insights on the origins and processes for the evolution of our solar system. These extraterrestrial materials contain highly complex microstructures due to the formation and structure evolution events spanning long periods of time. The comprehensive characterization on these samples, to extract multi-scale structural information, is especially crucial to support formation theories, understand material utilization possibility, and preparation for potential hazard mitigation. In addition to the microstructure, an understanding of the mechanical properties of these materials is also vital. Hence, an in-depth investigation on how microstructural phase distribution and their respective mechanical properties connect to macroscopic deformation behavior is required.</p> <p>In this study, a correlative microscopy-based methodology was used to study several celestial samples; meteorite Aba Panu (L3), meteorite Tamdakht (H5), and a lunar dust grain from mature sample 10084 returned by the Apollo 11 mission. X-ray microcomputed tomography (XCT) was utilized to acquire inherent 3D structural details from samples non-destructively. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) was used to further resolve finer structural features and compositional information to complete the correlative described above.</p> <p>Both ex situ and in situ compression experiments, in the XCT, were performed on machined cylindrical samples of Aba Panu meteorite. Structure development including crack initiation, propagation, and failure states were analyzed and correlated to the macroscopic stress-strain behavior. Direct 3D correlation on ex situ and in situ images of crack growth were used to obtain a comprehensive mechanistic understanding of crack development and deformation. Finally, nanoindentation was used to complement the 3D microstructural study, by acquiring mechanical properties of individual constituent phases.</p> <p><br></p>

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AbstractThe overall safety of dams depend on several stipulations. One of them is global stability of the dam, which is addressed with approaches like that in (RIDAS, 2017) (the Swedish power companies’ guidelines for dam safety). When designing a new dam, two global failure modes; sliding and overturning should be considered according to RIDAS. However, this is a simplification and other failure modes may exist, such as the combination of sliding and overturning failure. In this combined mode, the dam typically starts to overturn slightly, then as it looses its contact in the upstream area of the footprint, the dam starts to slide. This combined failure mode is yet to be fully addressed in design codes.One additional failure mode that may occur is an internal failure which is caused by material failure of the dam or where existing cracks govern the failure mode. Reinforced concrete structures are expected to crack and hence it likely that such failure mode may occur. The objective of this report is to understand the behavior of a pre-cracked buttress dam under typical loading conditions, and to analyze potential internal failure modes caused by these cracks. Moreover, the validity of using RIDAS design criteria for evaluating the safety of cracked concrete buttress dams will be examined. Finally, this report will study the influence of various possible cracks to study if these are critical and influence the overall dam safety.The stated objectives were investigated by performing analytical calculations and FE-analyses for three different geometries, where each geometry was analyzed with and without pre-existing cracks. The analytical calculations were carried out using MATLAB, to study the two global failure modes suggested by RIDAS: sliding and overturning for the selected geometries. FE-analyses were performed using BRIGADE Plus 6.2 software, where all geometries were studied for all potential global failure modes, including a combination of sliding and overturning failure modes. When comparing results of uncracked and cracked sections, whether it was obtained analytically or by FE-analyses, the influence of cracks in reducing the overall safety of the structure could be clearly highlighted. Moreover, the results comparing analytical solution using RIDAS and FE-analysis did not follow a uniform pattern, therefore, no concrete results could be concluded and further studies to develop more detailed analytical calculation methods were suggested. Finally, the cracks develop between the inspection gangway and the front-plate was proven to have larger influence on the residual mass of the dam, and thus, the overall safety of the dam.

The adhesion and durability of model epoxy/silane/SiO2/Si bonded systems were investigated under various conditions, including the type of surface preparation, pH of the environmental media, temperature, cyclic thermal stress, and external applied stress. The fundamental debond mechanism was studied for bonded systems exposed to selected environments. The bond failure mode was characterized by examining the failed bond surfaces using X-ray photoelectron spectroscopy. The effectiveness of combining the oxygen plasma treatment and silane coupling agent (SCA) derivatization in adhesion promotion for an epoxy bonded to a silicon surface was evaluated in this research. SCAs with different amine functionalities were studied. The oxygen plasma treatment time was varied systematically to achieve a different extent of oxidation on the Si wafer. The surface chemistry/composition of various silane derivatized Si surfaces was investigated. The studies revealed that SCA interaction with the Si surface was enhanced by the oxygen plasma pre-treatment of the Si substrates. XPS surface analysis results showed that the SCA/SiO2 ratio did not correlate strongly with the increase in oxygen plasma pretreatment time. However, for Si surfaces treated for longer oxygen plasma pretreatment times, more silanol groups may be available to interact with the hydrolyzed silanol groups on silane, resulting in a stronger SCA-Si attachment. Three different tests were employed to determine adhesion and durability of the model epoxy/SCA/SiO2/Si bonded specimens. The immersion test qualitatively evaluates the bond durability for various systems exposed to different chemical and thermal conditions. Second, a novel probe test was used to quantitatively determine adhesion under critical debonding conditions for bonded specimens with different SCA preparations. A general trend of bond durability varied in the manner SCA-2 > SCA-3 > SCA-1 > no silane. Bond durability also increased for samples: model epoxy/SCA modified/O2 plasma treated/Si as the oxygen plasma pre-treatment time increased. Third, bond durability was studied using the wedge DCB (double cantilever beam) test under subcritical debonding conditions with environment-assisted crack growth as a function of applied strain energy release rate. Higher crack velocity and the absence of a Gthreshold value were noted in tests at 70 oC. The Gthreshold value increased as the strength of the interface increased and as the chemical aggressiveness of the environment decreased. For tests involving 25 oC -70 oC thermal cycling, only limited crack growth was found. / Ph. D.

La investigación tiene como objetivo generar proponer un plan de mantenimiento basado en RCM para disminuir los tiempos de parada en la empresa Multiservicios Astolingón S.A.C., así mismo cuenta con los siguientes objetivos específicos: diagnosticar el estado actual de la maquinaria de la empresa mediante los reportes de fallas; identificar en que índice de criticidad de fallas se encuentra la etapa utilizando el análisis de criticidad, árbol de fallas, análisis de modo y efecto de fallo (AMEF); proponer el plan de gestión de mantenimiento en los equipos con mayor criticidad de la empresa, a partir de los resultados del análisis de criticidad, árbol de fallas, AMEF; y evaluar la reducción tiempo de paradas, comparando los tiempos del mantenimiento correctivo aplicado actualmente en la empresa, con el mantenimiento preventivo basado en RCM. En cuanto a la metodología es de enfoque cualitativo, la técnica utilizada es la indirecta, ya que se usará las herramientas de observación y revisión de reportes (como apoyo una entrevista). / The investigation has how to generate propose a maintenance plan based on RCM to reduce downtime in the company Multiservices Astolingón S.A.C., likewise has the following specific objectives: detect the current state of the company's machinery through failure reports; identify in which failure criticality index the stage is located using the criticality analysis, fault tree, failure mode and effect analysis (FMEA); proposes the maintenance management plan for the most critical equipment in the company, based on the results of the criticality analysis, fault tree, AMEF; and evaluate the reduction of downtime, comparing the times of corrective maintenance currently applied in the company, with preventive maintenance based on RCM. As for the methodology, it is of a qualitative approach, the technique used is indirect, since the tools of observation and review of reports will be used (as support for an interview).

L’émission de lumière est une puissante technique de localisation dans le domaine de l’analyse de défaillance des circuits intégrés. Depuis plusieurs années, elle est utilisée comme une technique capable de localiser et d’identifier des défauts émissifs, tels que les courants de fuites, en fonctionnement statique du composant. Cependant, l’augmentation d’intégration et des performances des circuits actuels implique l’apparition d’émissions de défauts dynamiques dus à l’utilisation de fréquences de fonctionnement de plus en plus élevées. Ces contraintes imposent une adaptation de la technique d’émission de lumière qui doit donc évoluer en même temps que l’évolution des circuits intégrés. C’est dans ce contexte que de nouveaux modes de détection, liés à l’émission de lumière, est apparu : PICA et TRE. Ainsi, les photons sont collectés en fonction du temps donnant ainsi une place importante à la technique par émission de lumière dynamique pour le debbug et l’analyse de défaillance en procédant à une caractérisation précise des défauts issus des circuits intégrés actuels. Pour répondre aux exigences dues à l’analyse du comportement dynamique des circuits intégrés, des méthodes ont été identifiées à travers la technique PICA et la technique d’émission en temps résolu connue sous le nom de technique mono-point TRE. Cependant, les techniques PICA et TRE sont exposées à un défi continu lié à la diminution des technologies et donc des tensions d’alimentation. Pour analyser des circuits de technologies futures à faible tension d’alimentation, il est nécessaire de considérer différentes approches afin d’améliorer le rapport signal sur bruit. Deux solutions sont présentées dans ce document : un système de détection optimisé et des méthodes de traitement de signal. / Light emission is a powerful technique for the characterization of failed integrated circuits. For years, faults have been identified in a static configuration of the device. Just by providing the power supply, abnormal current leakage could be located. With the growing complexity of devices, some fault may appear only in the middle of the test sequence. As a result the evolution of light emission was to use the same detector to acquire the image of a running circuit. A new mode of light emission came became available: PICA or picoseconds IC analysis. With this configuration, photons are collected as a function of time. This technique became mainstream for IC debug and failure analysis to precisely characterize IC. Light emission has also reached dynamic IC requirements through PICA and Single-point PICA also known as TRE. However, light emission and TRE is facing a continuous challenge with technologies shrinkage and its associated power supply voltage drop. To work with recent IC technologies with ultra low VDD voltage, it is necessary to take a different approach, to improve the signal to ratio. Two solutions are presented in this document: A best detection system and TRE and PICA signal processing development.

Node downtime and failed jobs in a computing cluster translate into wasted resources and user dissatisfaction. Therefore understanding why nodes and jobs fail in HPC clusters is essential. This paper provides analyses of node and job failures in two university-wide computing clusters at two Tier I US research universities. We analyzed approximately 3.0M job execution data of System A and 2.2M of System B with data sources coming from accounting logs, resource usage for all primary local and remote resources (memory, IO, network), and node failure data. We observe different kinds of correlations of failures with resource usages and propose a job failure prediction model to trigger event-driven checkpointing and avoid wasted work. We provide generalizable insights for cluster management to improve reliability, such as, for some execution environments local contention dominates, while for others system-wide contention dominates.