This dissertation examines life-time management of process and energetic devices in industrial practice, mainly in the area of steam power plants. Furthermore, it focuses on frequent damage mechanisms occurring in this area. It summarizes basics of damaging mechanisms occurring in the process industry area, their monitoring, evaluation and prediction. In the area of steam power plants, the main emphasize was placed on cumulative damage mechanisms. Within the dissertation, mechanisms of creep, fatigue, and their combinations were assessed. Major European standards were examined in order to discuss the amount of contained conservatism and their usability. Subsequently, attention was paid to the methods applicable for creep and fatigue combination evaluation. In the next step life-time monitoring and evaluation standard was discussed. The diagnostic software was created which includes creep, fatigue and creep-fatigue combination evaluation according to valid standards. For online life-time evaluation was proposed refined analytical solution for stress and strain calculation. To further extend the life-time management, the dissertation describes oxide scale damaging together with its evaluation and implementation into diagnostic software. The proposed software is extended by the material module which on the basis of defined materials allows easy and effective usage of material characteristics. For the purpose of refining life-time prediction accuracy, experimental device was schematically described. In addition, the device should be also able to verify used equations. Furthermore, the dissertation includes solution to industrially oriented cases. Firstly, a steam generator with damaged pipes was analyzed, afterwards damaged transferring pipeline. Further analyses deal with U-tube heat exchanger and its damaging. The causes of damage were discovered and corrective measures were proposed. The dissertation concludes with the summarization of potential activities for subsequent research in examined area.

No description available.

<p>The term Reclaimed Asphalt Pavement (RAP) is used to designate a material obtained from the removal of pavement materials. RAP is used across the US in multiple applications, largely on asphalt pavement layers. RAP can be described as a uniform granular non-plastic material, with a very low percentage of fines. It is formed by aggregate coated with a thin layer of asphalt. It is often used mixed with other granular materials. The addition of RAP to aggregates decreases the maximum dry unit weight of the mixture and decreases the optimum water content. It also increases the Resilient Modulus of the blend, but decreases permeability. RAP can be used safely, as it does not pose any environmental concerns. The most important disadvantage of RAP is that it displays significant creep. It seems that this is caused by the presence of the asphaltic layer coating the aggregate. Creep increases with pressure and with temperature, and decreases with the degree of compaction. Creep can be mitigated by either blending RAP with aggregate or by stabilization with chemical compounds. Fly ash and cement have shown to decrease, albeit not eliminate, the amount of creep. Mechanical stabilizing agents such as geotextiles may also be used.</p><p><br></p><p><br></p>

No description available.

[ES] El procedimiento de ensayo de fluencia es un proceso muy complicado, largo y que envuelve muchas variables. Por una parte, están las variables relativas al proceso de ensayo de fluencia como condiciones de contorno, condiciones ambientales, parámetros de ensayo como nivel de carga o prefisura inicial, entre muchos otros. Estas variables influyen ya de por si lo suficiente en los resultados experimentales obtenidos en los ensayos sumado a la variabilidad intrínseca del hormigón reforzado con fibras. La duración mínima requerida en este tipo de ensayos y el espacio físico necesario, así como asegurar las condiciones ambientales, supone muchas veces un importante reto y consumo de recursos y espacio, lo que ha frenado hasta ahora la inversión en investigación para abordar este tema. Para ello, tras un exhaustivo estudio del estado del arte y partiendo de una metodología a flexión existente, se han desarrollado varias campañas experimentales para evaluar el efecto de los parámetros básicos de ensayo, la construcción del bastidor y el análisis de los resultados experimentales obtenidos de aplicar la metodología. Con todo ello se pretende obtener parámetros de ensayo diseñados para caracterizar el efecto de la fluencia en estado límite de servicio, así como unificar criterios y procesos del ensayo diseñando un procedimiento que pueda ser estandarizado. Por otra parte, existe la dificultad añadida de entender qué sucede dentro de la sección durante el ensayo de fluencia más allá de la variación en abertura de fisura. La redistribución de esfuerzos que se produce dentro de la sección fisurada durante el ensayo de fluencia a flexión es una incógnita. Este trabajo pretende también arrojar algo de luz estudiando tanto la evolución de la abertura de fisura como las deformaciones en la zona comprimida del hormigón. Se han diseñado campañas experimentales para evaluar simultáneamente las deformaciones de tracción (abertura de fisura) y las deformaciones de compresión (zona comprimida del hormigón) de modo que permitan evaluar tanto la contribución de la fluencia a compresión sufrida por la zona comprimida de hormigón en las mediciones de abertura de fisura como la evolución de la profundidad de la fibra neutra de la sección fisurada durante el ensayo a flexión. En este contexto, el resultado es una nueva propuesta metodológica de fluencia a flexión consensuada y capaz de caracterizar el comportamiento a flexión de hormigones reforzados con fibra en estado fisurado, así como algunas herramientas como la base de datos de fluencia que ayudan a la interpretación de los resultados experimentales y puedan contribuir a la consideración de estas deformaciones por las distintas normativas internacionales en su fase de diseño. / [CA] El procediment d'assaig de fluència és un procés molt complicat, llarg i que embolica moltes variables. D'una banda, estan les variables relatives al procés d'assaig de fluència com a condicions de contorn, condicions ambientals, paràmetres d'assaig com nivell de càrrega o prefissura inicial, entre molts altres. Aquestes variables influeixen ja de per si prou en els resultats experimentals obtinguts en els assajos sumat a la variabilitat intrínseca del formigó reforçat amb fibres. La duració mínima requerida en aquesta mena d'assajos i l'espai físic necessari, així com assegurar les condicions ambientals, suposa moltes vegades un important repte i consum de recursos i espai, la qual cosa ha frenat fins ara la inversió en investigació per a abordar aquest tema. Per a això, després d'un exhaustiu estudi de l'estat de l'art i partint d'una metodologia a flexió existent, s'han desenvolupat vàries campanyes experimentals per a avaluar l'efecte dels paràmetres bàsics d'assaig, la construcció del bastidor i l'anàlisi dels resultats experimentals obtinguts d'aplicar la metodologia. Amb tot això es pretén obtindre paràmetres d'assaig dissenyats per a caracteritzar l'efecte de la fluència en estat límit de servei, així com unificar criteris i processos de l'assaig dissenyant un procediment que puga ser estandarditzat. D'altra banda, existeix la dificultat afegida d'entendre què succeeix dins de la secció durant l'assaig de fluència més enllà de la variació en obertura de fissura. La redistribució d'esforços que es produeix dins de la secció fisurada durant l'assaig de fluència a flexió és una incògnita. Aquest treball pretén també llançar una mica de llum estudiant tant l'evolució de l'obertura de fissura com les deformacions en la zona comprimida del formigó. S'han dissenyat campanyes experimentals per a avaluar simultàniament les deformacions de tracció (obertura de fissura) i les deformacions de compressió (zona comprimida del formigó) de manera que permeten avaluar tant la contribució de la fluència a compressió patida per la zona comprimida de formigó en els mesuraments d'obertura de fissura com l'evolució de la profunditat de la fibra neutra de la secció fisurada durant l'assaig a flexió. En aquest context, el resultat és una nova proposta metodològica de fluència a flexió consensuada i capaç de caracteritzar el comportament a flexió de formigons reforçats amb fibra en estat fisurado, així com algunes eines com la base de dades de fluència que ajuden a la interpretació dels resultats experimentals i puguen contribuir a la consideració d'aquestes deformacions per les diferents normatives internacionals en la seua fase de disseny. / [EN] Creep testing methodology on fibre-reinforced concrete is a long and complex process involving multiple variables. On the one hand, creep testing parameters such as pre-cracking level and creep index or stress sustained level, as well as boundary and environmental conditions, can be found among other variables. Variations on these parameters, together with the intrinsic variability of FRC due to the random fibre distribution of FRC, have a significant impact on the experimental results obtained among the existent methodologies. The long duration of the creep test and the required space in the facilities laboratories as the environmental conditions to keep during the creep test entail a significant challenge and outlay in terms of both space and expense resources that have reduced the research investment on this topic. Thus, after an exhaustive analysis of the state-of-the-art and starting from an existent creep testing methodology, several experimental programmes were developed to assess the effect of main creep testing parameters and the influence of creep frame construction as well as different procedure steps on the experimental results when the flexure creep testing methodology is applied. This work intends to define test parameters focused on characterising the effect of creep in the service limit state (SLS), as well as to unify criteria and processes of creep test, developing a procedure that can be standardised. On the other hand, it is difficult to understand what happens within the cross-section during the creep test beyond the crack opening variation. The stress redistribution within the cross-section during the creep test is still unknown. This work also aims to shed some light by studying both the evolution of the crack opening and the compressive deformations in the compressed concrete zone. Experimental campaigns have been designed to assess both the tensile (crack opening) and compression (compressive strains) creep simultaneously that, allow to determine the contribution of compressive creep in the concrete area in the delayed crack opening and to assess the evolution of the neutral fibre position of the cross-section during the flexure creep test duration. In this context, the result of this PhD research is a new flexure creep methodology proposal able to characterise long-term behaviour in flexure of cracked fibre-reinforced concrete, as well as some valuable tools such as the creep database that will help to understand experimental results and to contribute to consider delayed deformations in the international standards in the service state limit design. / Llano Torre, A. (2023). Improvements in test methodology and characterisation of long-term flexure behaviour of fibre-reinforced concrete [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/192111

[pt] A fluência do concreto é um fenômeno físico complexo e apresenta características diferentes das observadas na maioria dos materiais. Apesar dos diversos estudos desenvolvidos, a compreensão desse fenômeno ainda não é completa e os modelos disponíveis na literatura para simulação numérica variam em complexidade, número de parâmetros e condições que garantem a sua aplicabilidade. Os estudos mais recentes desenvolvidos por Bažant se destacam e reportam boa concordância com resultados experimentais. Seus fundamentos são utilizados no desenvolvimento do modelo de fluência básica linear adotado neste trabalho. Dessa forma, realiza-se uma revisão da viscoelasticidade linear, na qual apresentam-se os modelos reológicos, as relações constitutivas e as principais hipóteses adotadas no estado multiaxial de tensão. Discute-se as propriedades da fluência do concreto e apresenta-se a teoria da solidificação, que tem por objetivo representar a evolução ao longo do tempo das propriedades aparentes do concreto. A partir desse estudo, adota-se um modelo de fluência básica com envelhecimento definido por cadeias de Kelvin e desenvolve-se um algoritmo para integração numérica da taxa de deformação. O modelo é implementado em um programa de elementos finitos e validado com resultados experimentais de fluência linear. Por fim, este trabalho propõe a modelagem da não linearidade da fluência do concreto com o emprego de elementos de interface coesiva. Apresenta-se uma metodologia para calibração dos parâmetros envolvidos, e compara-se a resposta do modelo com resultados experimentais de um ensaio de fluência na flexão. Os resultados obtidos numericamente mostram boa concordância com os resultados experimentais tanto para o caso de fluência linear pura quanto para o caso de fluência e dano. / [en] Concrete creep is a complex physical phenomenon and has different characteristics from those observed in most materials. Despite several studies developed, the understanding of this phenomenon is not yet complete and the models available in the literature for numerical simulation vary in complexity, number of parameters and conditions that ensure their applicability. The latest studies developed by Bazant stand out and report good agreement with experimental results. Their fundamentals are used in the development of the linear basic creep model adopted in this work. Thus, it is carried out a review of linear viscoelasticity, in which the rheological models, the constitutive relationships, and the main assumptions adopted in the multi-axial state of stress are presented. Concrete creep properties are discussed and the solidification theory is presented, aiming to represent the development over time of the apparent concrete properties. Based on this study, a basic creep model with aging defined by Kelvin chains is adopted and an algorithm for numerical integration of the strain rate is developed. The model is implemented in a finite element program and validated with experimental linear creep results. Finally, this work proposes modeling the nonlinear dependence of concrete creep with the use of cohesive interface elements. A methodology for calibrating the parameters involved is presented, and the model response is compared with the experimental results of a bending creep test. The numerically obtained results show good agreement with the experimental results for both the pure linear creep and the creep and damage.

In the precast construction market, the competitive situation is significantly affected by price, cost, productivity, and quality factors. Since self-consolidating concrete (SCC) was first introduced to the concrete industry in the late 1980s, it has been used worldwide in variety of applications. Despite the documented technical and economic advantages of SCC in precast, prestressed applications, the use of SCC has been limited in some countries due to some technical uncertainties of such innovative material. To explore some unsolved issues related to SCC and to contribute to a wider acceptance of SCC in precast, prestressed applications, this study was undertaken to assess the effect of mixture proportioning and material characteristics on the performance of SCC and recommend performance-based specifications for use of SCC in the precast, prestressed applications. The thesis presents an experimental program that contains four parts: (1) a parametric study to evaluate the influence of binder type, w/cm, coarse aggregate type, and coarse aggregate nominal size on the modulus of elasticity and compressive strength developments; (2) a parametric study to evaluate the effect of mixture proportioning and material characteristics on fresh and hardened properties of SCC; (3) a fractional factorial design to identify the relative significance of primary mixture parameters and their coupled effects on SCC properties; and (4) a field validation using full-scale AASHTO Type II girders cast to investigate constructability, material properties, and structural performance (the latter part was carried out by the research team of Professor Denis Mitchell at McGill University). Based on the experimental test results, SCC exhibits similar compressive strength and modulus of elasticity to that of conventional high-performance concrete (HPC) of normal slump consistency. SCC and HPC mixtures made of a given binder type exhibit similar autogenous shrinkage. However, SCC exhibits up to 30% and 20% higher drying shrinkage and creep, respectively, at 300 days compared to HPC made with similar w/cm but different paste volume. The results of the experiment program show that among the investigated material constituents and mix design parameters, the w/cm has the most significant effect on mechanical and visco-elastic properties. The binder content, binder type, and sand-to-total aggregate ratio (S/A) also have considerable effect on those properties. The thickening-type viscosity modifying admixture (VMA) content (0 to 150 ml/100 kg CM) does not significantly affect mechanical and visco-elastic properties. Based on the findings, some mixture parameters regarding the overall performance of SCC designated for precast and prestressed applications can be recommended: SCC made with relatively low w/cm (such as 0.34 vs. 0.40) should be selected to ensure desirable compressive strength, modulus of elasticity (MOE), flexural strength, as well as less drying shrinkage and creep; the use of crushed aggregate with 12.5 mm MSA is suggested since it provides better mechanical properties of SCC compared to gravel; the use of low S/A (such as 0.46 vs. 0.54) to secure adequate mechanical and visco-elastic properties is recommended; the use of thickening-type VMA can help to secure robustness and stability of the concrete in the case of SCC proportioned with moderate and relatively high w/cm; and the use of Type MS cement can lead to lower creep and shrinkage than Type HE cement and 20% Class F fly ash. However, SCC mixtures made with Type HE cement and 20% Class F fly ash can result in better workability and mechanical properties. Therefore, it is recommended to use Type HE cement and 20% Class F fly ash and reduce binder content (such as 440 kg/m[exposant 3] vs. 500 kg/m[exposant 3]) to assure better overall performance of SCC. Validation on full-scale AASHTO-Type II girders using two HPC and two SCC mixtures show that girders casting with SCC can be successfully carried out without segregation and blocking for the selected optimized mixtures. The surface quality of the girders cast with SCC is quite satisfactory and of greater uniformity than girders cast with HPC. Both HPC and SCC mixtures develop similar autogenous shrinkage for mixtures made with similar w/cm. Again, the two evaluated SCC mixtures develop about 20% greater drying shrinkage than comparable HPC mixtures. Modifications of existing models to assess mechanical and visco-elastic properties of SCC used in the precast, prestressed applications are proposed. Based on the comparisons of various code provisions, the ACI 209 and CEB-FIP codes with suggested material coefficients can be recommended to estimate compressive strength. The modified AASHTO 2007 model can be used for predicting the elastic modulus and flexural strength. The AASHTO 2004 and 2007 models with suggested material coefficients can be used to estimate drying shrinkage and creep, respectively. The CEB-FIP 90 code model can be used to predict both drying shrinkage and creep. Finally, the modified Tazawa and Miyazawa 1997 model with material modifications can be used to estimate autogenous shrinkage of SCC.

Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Concrete water retaining structures (WRS) in South Africa are under scrutiny due to the numerous durability problems that they have experienced lately; despite the efforts by local and national authorities in conserving these structures. At the heart of these problems are the creep and shrinkage phenomena. While shrinkage is the reduction of concrete volume with time, creep is defined as the time-dependent increase of concrete strain under constant or controlled stress. Both phenomena are affected by conditions to which WRS are exposed hence their accurate prediction is required. Numerical models have been developed to calculate the extent to which concrete creeps or shrinks over time. The objective of this thesis is to identify which of these models is better equipped to be used in South African WRS design. This is achieved through a systematic method that involves an investigation into the contents of these models and a statistical comparison of model calculations to WRS representative data. In partnership with reputable universities, a pioneer experimental creep and shrinkage data base is created in this project from which the WRS related data is selected. While investigating the contents of the numerical models, their applicability to South African WRS is identified and the integrity of model contents is assessed. Indeed, a few irregularities are found in the process and are presented in this thesis. The model calculations are statistically compared to data in the form of individual experiments as well as in the form of groups of experiments with similar concretes to find the ideal prediction model for different types of concretes as well. Also pioneered in this project is a weighted criteria and point system in which the findings of the model content assessment and statistical evaluations are incorporated. It is based on this system that conclusions are drawn and the most suitable prediction model for WRS design in South Africa is selected.

published_or_final_version / abstract / Civil Engineering / Doctoral / Doctor of Philosophy

Metallic materials play important roles in providing electrical, thermal, and mechanical functions in electronic devices and systems. The understanding of the electrical-thermal-mechanical interaction caused by the passage of electric current with high density is important to improve the performance and reliability of electronic assembly and packaging. The electromechanical interaction on the deformation behavior of copper and tin is studied in this work. The electromechanical response of Cu strips was studied by passing a DC electric current. The electric resistance linearly increased with time before the occurrence of electric fusing. The electrothermal interaction led to the buckling of the Cu strips with the maximum deflection increasing with the increase of the electric current density. The total strain was found to be proportional to the square of the electric current density. A power law relation was used to describe the dependence of the time-to-fusing on the electric current density. Using the nanoindentation technique, the effect of electric current on the indentation deformation of copper and tin was studied. The reduced contact modulus of copper and tin decreased with increasing the electric current density. With the passage of a DC electric current, the indentation hardness of copper increased slightly with increasing electric current density. With the passage of an AC electric current, the indentation hardness of copper decreased with increasing the indentation deformation. With the passage of a DC electric current, the indentation hardness of tin decreased with increasing the indentation load, showing the normal indentation size effect. Both the limit of infinite depth and the characteristic length were dependent on the electric current density. Using the tensile creep technique, the creep deformation of pure tin was studied with the passage of a DC electric current. The steady state creep rate increased with the increase in temperature, tensile stress and electrical current density. For the same tensile stress and the same chamber temperature, the steady state creep rate increased linearly with the square of the electric current density. The electric current density has no significant effect on the stress exponent and activation energy of the tensile creep of tin for the experimental conditions.