Metallic utility poles, light poles, and mast arms are intermittently damaged by vehicle collision. In many cases the vehicular impact does not cause immediate failure of the structure, but induces localized damage that may result in failure under extreme service loadings or can promote degradation and corrosion within the damaged region. Replacement of these poles is costly and often involves prolonged lane closures, service interruption, and temporary loss of functionality. Therefore, an in situ repair of these structures is required. This thesis examines the failure modes of damaged metallic poles reinforced with externally-bonded fiber reinforced polymer (FRP) composites. Several FRP repair systems were selected for comparison, and a set of medium and full-scale tests were conducted to identify the critical failure modes. The material properties of each component of the repair were experimentally determined, and then combined into a numerical model capable of predicting global response. Four possible failure modes are discussed: yielding of the unreinforced substrate, tensile rupture of the FRP, compressive buckling of the FRP, and debonding of the FRP from the substrate. It was found that simple linear, bilinear, and trilinear stress-strain relationships accurately describe the response of the composite and substrate components, whereas a more complex bond-slip relationship is required to characterize debonding. These constitutive properties were then incorporated into MSC.Marc, a versatile nonlinear finite element program. The output of the FEM analysis showed good agreement with the results of the experimental bond-slip tests.

Yes / Failure Modes and Effect Analysis (FMEA) is a proactive, highly structured, and systematic approach for failure analysis. It has been also applied as a risk assessment tool, by ranking potential risks based on the estimation of Risk Priority Numbers (RPNs). This paper develops an improved FMEA methodology for strategic risk analysis. The proposed approach combines the Analytic Hierarchy Process (AHP) technique with the Exponential and Weighted Geometric Mean method (EWGM) to support risk analysis. AHP is applied to estimate the weights of three risk factors: Severity (S), Occurrence (O) and Detection (D), which integrate the RPN for each risk. The EWGM method is applied for ranking RPNs. Combining AHP with EWGM allows avoiding repetition of FMEA results. The results of the developed methodology reveal that duplication of RPNs has been decreased, and facilitating an effective risk ranking by offering a unique value for each risk. The proposed methodology focuses not only on high severity values for risk ranking but also it considers other risk factors (O and D), resulting in an enhanced risk assessment process. Furthermore, the weights of the three risk factors are considered. In this way, the developed methodology offers unique value for each risk in a simple way which makes the risk assessment results more accurate. This methodology provides a practical and systematic approach to support decision-makers in assessing and ranking risks that could affect long-term strategy implementation. The methodology was validated through the case study of a power plant in the Middle East, assessing 84 risks within 9 risk categories. The case study revealed that top management should pay more attention to key risks associated with electricity price, gas emissions, lost-time injuries, bad odor, and production. / This research has been supported by Hashemite University, Jordan.

Sweetgum, Liquidambar styraciflua, is a diffuse-porous hardwood occurring in the southeastern United States. In this observational study, trees from two plantations of sweetgum were evaluated for mechanical properties. The two plantations were similar in age, soil type, competition control, and water availability, but differed in nutrient availability, growing season, and growth rate. Three trees representing different crown classes were removed from both plantations. Each tree was sampled for compression strength parallel to grain along the height of the merchantable stem. Oven-dry specific gravity was then calculated for each sample. The results indicate that young sweetgum trees grow weaker wood than mature trees. It was observed that dominant trees were stronger and denser than other trees. Denser wood was formed in the plantation with the shortest growing season and smallest growth rate. Three of six trees showed significant correlations of strength and stiffness with height in the tree. / Master of Science

A deposição de filmes finos resistentes ao desgaste é uma prática realizada com bastante frequência para melhorar o comportamento tribológico (atrito, desgaste, lubrificação) de diferentes peças e componentes. Afim de se garantir o adequado funcionamento do sistema revestido (substrato+filme), é importante avaliar o comportamento mecânico do mesmo. Um método para avaliação e estudo do comportamento mecânico destes sistemas é o ensaio de riscamento. O ensaio é utilizado para analisar a fratura superficial do revestimento (falha chamada coesiva), ou a resistência à adesão (falha chamada adesiva), e os modos de falha de revestimentos duros (HV>=5 GPa) e finos (<=30 ?m), depositados sobre substratos cerâmicos ou metálicos. A caracterização de alguns modos de falha nos sistemas revestidos está relacionada com modelos qualitativos de tensões presentes na região de contato e nas bordas do riscamento. Neste trabalho, foi estudado o comportamento das tensões Sxx e Szz desenvolvidas durante o riscamento de sistemas compostos por combinações de revestimentos/substratos. O trabalho foi baseado no desenvolvimento de modelos de simulação em 3D e 2D, utilizando o método dos elementos finitos (MEF), nos quais, uma partícula rígida com características de indentador Rockwell C, aplica carga progressiva até 2 N, ao longo de uma distância de 0,5 mm. No estudo, variou-se a dureza, traduzida em valores de tensão de escoamento do revestimento e do substrato, da mesma forma, analisou-se o efeito da tensão residual do revestimento, o efeito da espessura, o atrito, e a rugosidade, na superfície e na interface do sistema. O fato de obter valores de tensão que ultrapassam o valor do escoamento do revestimento pressupõe a possível ocorrência de falhas nos sistemas revestidos. Os resultados obtidos por simulação indicaram que as combinações de revestimento com tensão de escoamento baixa (Sy<3000 MPa) levam a experimentar tensões ao nível da tensão de escoamento do revestimento. Os revestimentos com tensão de escoamento Sy>5000 MPa apresentaram valores de tensão inferiores aos da tensão do revestimento, bem como o uso de tensão residual de -3 GPa no revestimento, assim como o aumento da espessura do revestimento têm grande importância nos sistemas revestidos, em particular nos casos em que a tensão de escoamento no revestimento é Sy>=5000MPa. O efeito do coeficiente de atrito leva à obtenção de valores de tensão (Sxx ou Szz) suficientemente altos na maioria das combinações, sendo esta a variável de estudo que levou ao maior número de vezes que foi atingido o valor da tensão de escoamento do revestimento. Da mesma forma, a rugosidade afeta os valores de tensão Sxx (interior do sulco). Ao aumentar a rugosidade do sistema aumenta a possibilidade de ultrapassar valores da tensão do revestimento na superfície e na interface do conjunto. Finalmente, pela complexidade do número de variáveis que afetam o ensaio, a simulação numérica sugere que o fato de analisar unicamente a dureza dos materiais, assim como as diferentes variáveis de forma isolada, não permite a reprodução de um mapa de falhas próximo ao proposto na literatura. / The deposition of wear resistant thin films is a common practice to improve the tribological behavior (friction, wear, lubrication) of several mechanical components. In order to guarantee the adequate performance of the coated systems, it is important to evaluate the mechanical behavior. A method for evaluation and study of the coated systems is the scratch test. The test is used to analyze the fracture of the coating (cohesive failure), or the adhesion of the coating (adhesive failure), and the failure modes of hard coatings (HV>=5 GPa) and thin (<=30 ?m) deposited on ceramic or metallic substrates. The characterization of some failure modes in coated systems is related to qualitative stress models at the contact region and the scratch edges. In this work, the behavior of the Sxx and Szz stresses developed during the scratch test was analyzed in different combinations of coatings/substrates. The work was based on the development of 3D and 2D simulation models using the finite element method (FEM). In the simulation, a rigid particle (with the geometry of Rockwell C indenter) applied progressive load to 2N along a 0.5 mm distance. In the study, the hardness was expressed as yield stress values in the coating and the substrate. In addition, it was examined the effect of coating residual stress (-3 GPa), as well as the effect of the thickness, the friction coefficient, and roughness of the surface and interface in the stresses behavior. The fact of obtaining tension values, which exceed the yield stress of coating implies the possible occurrence of failure. The results obtained by simulation indicated that the coating combinations with low yield stress (Sy < 3000 MPa) lead to Sxx and Szz stress values in the level of the coated yield stress. The coatings with yield stress Sy > 5000 MPa enable to obtain low Sxx and Szz values. The use of the residual stresses (-3 GPa) as well as increasing the thickness of the coating are very important factors in the coated systems, especially in the case of coatings with Sy > 5000 MPa. The effect of the friction coefficient leads to stress values (Sxx or Szz) sufficiently high in most of the combinations. This factor is the most important variable leading to the greater number of times that the value of the coating yield stress was reached. The roughness is responsible for Sxx stress values (inside groove). Increasing the roughness of the system increased the possibility of exceeding stress values in the surface and interface coating. Finally, by the complexity of the number of variables that affect the scratch test, the numerical simulation suggests that the fact of only analyzing the hardness of materials, as well as other isolated variables of the scratch test does not allow reproduction of a map of failures similar to that proposed in the literature.

Neste trabalho, são desenvolvidas novas técnicas aproximadas de análise de confiabilidade para grelhas de concreto armado levando-se em consideração as probabilidades de falha de vários modos importantes. Realiza-se um acoplamento entre os métodos de Monte Carlo, elementos finitos e procedimentos de otimização para considerar esses modos de falha importantes e classificá-los. Esse acoplamento também permite a redução do número de chamadas ao modelo de elementos finitos. Os cenários de falha são caracterizados como o encurtamento excessivo do concreto e o alongamento do aço. Estes cenários determinam a capacidade última da estrutura, e podem ser representados por um coeficiente escalar que multiplica todas as ações presentes na estrutura. Para a determinação desses estados estruturais últimos, um procedimento incremental-iterativo é utilizado. A análise de confiabilidade é realizada em diferentes conjuntos de realizações aleatórias das variáveis de projeto. O conjunto de respostas estruturais e de realizações permite a determinação dos coeficientes da superfície de respostas da estrutura. O acoplamento realizado permite também o tratamento com estruturas de concreto com elevado número de modos de falha. Aplicam-se as técnicas em exemplos de grelhas de concreto armado / In this work, new local approaches of reliability analysis applied to reinforced concrete grid structures are developed, taking into account several critical cross-section failure probabilities. Monte Carlo simulations are coupled with finite element analyses and optimization techniques with techniques to take into account the failure in the most important cross-sections, in order to classify the severity of failure modes. The failure scenario is depicted when either a concrete fiber or a steel bar reaches the predefined conventional limit. This scenario gives the structural ultimate capacity, which can be represented by a scalar coefficient multiplying all the loads acting on the structure. To achieve the failure scenario, an incremental and iterative procedure is used. To carry out the reliability analysis, the mechanical analysis has to be performed for different sets of random variable realizations of the mechanical, material and geometrical properties. The set of ultimate coefficients obtained from several mechanical analyses defines the response surface. The coupling between Monte Carlo simulations and response surface techniques applied in this work aims to reduce significantly the number of the finite element model calls, and hence to deal with real, or high-scale, reinforced concrete grids where large number of failure components can be found. The proposed procedure is then applied to reinforced concrete grids in order to show some more complex reinforced concrete examples

Enfrentar situações de falha é o principal desafio do engenheiro estrutural. Parece paradoxal, mas a fim de obter um projeto bem sucedido, o engenheiro estrutural deve estudar e examinar todos os possíveis modos de falha de uma estrutura. Na otimização estrutural não é diferente. Assim, na otimização estrutural deve-se considerar os custos esperados de falha. No projeto de engenharia estrutural, economia e segurança são aparentemente objetivos conflitantes. No entanto, quando custos esperados de falha são considerados, nota-se que investimentos em segurança são necessários a fim de não arcar com os custos esperados de falha. O ponto ideal de compromisso pode ser encontrado por uma otimização de risco, onde a função objetivo inclui todos os custos ao longo do ciclo de vida da estrutura: construção, operação, manutenção inspeção, descarte e as consequências de falha esperadas. Este último é um remanescente que não pode ser desconsiderado dos modos de falha contra os quais a estrutura precisa ser projetada. Esta dissertação aborda a otimização de sistemas estruturais simples, considerando o equilíbrio entre modos de falha concorrentes, tais como escoamento (esmagamento), flambagem e snap-through. O estudo mostra como os diferentes modos de falha, associados a diferentes custos de falha, levam a diferentes projetos ótimos. Uma estrutura de treliça plana é estudada como exemplo de aplicação. A forma (posições nodais) e tamanho dos elementos são consideradas como variáveis de projeto. Resultados mostram que projetos ótimos suficientemente diferentes são obtidos quando o equilíbrio entre modos de falha concorrentes é alterado. / Defying failure is the primary challenge of the structural engineer. It sounds paradoxical, but in order to achieve a successful design, the structural engineer must think about and account for all possible failure modes of a structure. This is not different in structural optimization. Hence, in structural optimization one has to consider the expected costs of failure. In structural engineering design, economy and safety are apparently conflicting goals. However, when expected costs of failure are considered, one notes that investments in safety are necessary in order not to pay for the expected costs of failure. The optimum point of compromise can be found by a risk optimization, where the objective function includes all costs over the life-cycle of the structure: construction, operation, inspection maintenance, disposal, and the expected consequences of failure. The latter are an undeletable remainder of the failure modes that the structure needs to be designed against. This paper addresses the optimization of simple structural systems, considering the balance between competing failure modes such as yielding (squashing), buckling and snap-through. The study shows how different failure modes, associated to different costs of failure, lead to different optimal designs. A plane truss structure is studied as application example. The shape (nodal positions) and member size are considered as design variables. Results show that quite different optimal designs are obtained when the balance between competing failure modes is changed.

This thesis deals with the reliability analysis of a fuel pump driver circuit (FPDC), which regulates the amount of fuel pumped to a turbojet engine. Reliability analysis in such critical circuits has great importance since unexpected failures may cause serious financial loss and even human death. In this study, two types of reliability analysis are used: &ldquo / Worst Case Circuit Tolerance Analysis&rdquo / (WCCTA) and &ldquo / Failure Modes and Effects Analysis&rdquo / (FMEA). WCCTA involves the analysis of the circuit operation under varying parameters in their tolerance bands. These parameters include the resistances of the resistors, operating temperature and voltage input value. The operation of FPDC is checked and the most critical parameters are determined in the worst case conditions. While performing WCCTA, a method that guarantees the exact worst case conditions is used rather than probabilistic methods like Monte Carlo analysis. The results showed that the parameter variations do not affect the circuit operation unfavorably / operating temperature, voltage input variation and tolerance bands for the resistances are fairly compatible with the circuit operation. FMEA is implemented according to the short circuit and open circuit failures of all the electronic components used in FPDC. The components whose failure has catastrophic effect on the circuit operation have been determined and some preventive actions have been offered for some catastrophic failures.

In this thesis different mechanical properties for shotcrete (sprayed concrete) such as compression strength, bond strength, bending tensile strength, elastic modulus, free and restrained shrinkage as a function of its age was investigated. One of the main issues was to investigate the difference between ordinary cast concrete and shotcrete. Reliable material data for young and hardening shotcrete is scarce which in the past have made such comparisons difficult. Also, less accurate data representative for cast concrete has often been used in numerical modelling and design analyses. The focus of the project has particularly been on the properties bond strength and restrained shrinkage for which two new testing methods has been developed and evaluated. Microstructural studies have also been performed as a complement to the bond strength testing. The bond to rock is one of the most important properties for shotcrete used as rock reinforcement. During the very first time after spraying the physical properties and the bond to the rock depend on the set accelerator and the micro structure that is formed. The investigation of early age bond strength of shotcrete is of great importance both from a production perspective and a safety perspective. The newly developed method was tested and evaluated and proved that it can be used for bond strength testing already from a couple of hours after shotcreting. The bond, or adhesion, depends on several factors such as texture of the rock, the type of accelerator, application technique, etc. In this work the development of the microstructure in the interfacial transition zone (ITZ) and strength of the bond was investigated. The results show that the bond strength is related to the hydration process, i.e. the strength gain of the shotcrete. The early development of the ITZ was here studied using a scanning electron microscope (SEM) making it possible to observe changes over time, before and after proper cement hydration. Restrained shrinkage cracking of shotcrete, especially in the case of shotcrete sprayed on soft drains that are parts of a tunnel lining not continuously bonded to the rock, can be detrimental for the sustainability of an infrastructure tunnel system. Maintenance and repair costs can be high over time. It is shown that the developed test method realistically captures the behaviour of shotcrete drains on hard rock in situ. The method can be used in the evaluation of different technical solutions for avoiding or minimizing shrinkage cracks in shotcreted soft drains. It can also be used to assess the performance of shotcrete fully bonded to a rock surface, with respect to the ability to prevent cracking or to distribute possible shrinkage damage into several fine cracks instead of one wide. / <p>QC 20140526</p>

Actuellement, dans les plateformes aérospatiales, le nombre et le besoin d’intégration des équipements électriques et électroniques sont grandissant du fait que leurs fonctions nécessitent de plus en plus de puissance. L’objectif de minimisation des coûts et surtout la disponibilité des dispositifs électroniques forcent les concepteurs et les fabricants de ces plateformes à s’orienter vers des produits commerciaux (dits grand public). La fiabilité des boîtiers des composants de puissance doit être évaluée dans les environnements sévères des applications aérospatiales. Une dizaine de composants électroniques de puissance a été sélectionnée en fonction de leur disponibilité et l’adéquation de leurs performances électriques et thermiques aux exigences des applications aérospatiales. Ces composants intègrent différents types de semi-conducteurs tels que le silicium, le carbure de silicium et le nitrure de gallium. Tout d’abord, une étude a été menée sur les potentiels modes et mécanismes de défaillance de ces composants électroniques de puissance dans ces environnements. Elle a permis de mettre en place plusieurs procédures de vieillissement accéléré ainsi que le développement de deux bancs de tests pour suivre électriquement le vieillissement de ces composants. Ces tests ont été menés sur deux diodes Schottky SiC, commercialisées par deux fabricants, regroupant les technologies des boîtiers des composants électroniques de puissance. Les analyses de défaillance ont tout d’abord mis en évidence une immaturité de la technologie de la jonction Schottky des puces SiC de l’une des deux diodes soumis à une tension inverse. Ces défaillances sont attribuées à la destruction partielle de la structure Schottky et indique une reproductibilité non maitrisée de la fabrication des puces de ce composant. Ensuite, ces analyses ont mis en évidence plusieurs mécanismes de vieillissement lors de tests simulant des régimes « On-Off » des applications (cycles thermiques de puissance). Celui considéré comme la cause de la défaillance est la fissuration de la soudure des fils d’interconnexion avec la puce. Une loi pouvant décrire la fissuration des interconnexions a été identifiée à la suite des évolutions des cycles thermiques de puissance à l’approche de la défaillance. L’étude de ces évolutions a permis de démarrer l’élaboration d’un modèle physique de défaillance adapté aux interconnexions de la puce en vue d’estimer la durée de vie des composants commerciaux. / Currently, in the aerospace platforms, the number and the need for integration of the electric and electronic equipment are growing because their functions require more and more power. The goal of cost minimization and mostly the availability of power electronic devices push the designers and the manufacturers of these platforms moving towards commercial products (Component Off-The Shelf). The packaging reliability of power electronic components must be assessed in harsh environments of aerospace applications. A dozen of power electronic components have been selected in accordance with their availability and with the adequacy of their electrical and thermal performances according to the requirements of aerospace applications. These components integrate different types of semi-conductors such as silicon, silicon carbide and gallium nitride. Foremost, a study has been leaded on the potential failure modes and mechanisms of these power electronic components in these environments. It has permitted to put in place several procedures of accelerated ageing and the development of two test benches to electrically monitor the ageing of these components. These tests have been carried on two SiC Schottky diodes, marketed by two manufacturers, gathering the technologies of the packaging of power electronic components. The failure analyses have first highlighted an immaturity of the Schottky junction technology of the SiC die of one of the two diodes subjected to a reverse voltage. These failures are attributed to the partial destruction of the Schottky structure and indicate a not mastered reproducibility of the die manufacturing of these components. Then, these analyses have highlighted several ageing mechanisms during tests simulating « On-Off » power of applications (power thermal cycles). One considered as the failure cause is the cracking of the welding of the wire bonding with the die. A behavioral law that can describe the cracking of the interconnections has been identified according to the evolutions of the power thermal cycles when near to failure. The study of these evolutions have permitted to start the elaboration of a physical model of failure adapted to the die interconnections in order to estimate the lifetime of commercial components.

Neste trabalho, são desenvolvidas novas técnicas aproximadas de análise de confiabilidade para grelhas de concreto armado levando-se em consideração as probabilidades de falha de vários modos importantes. Realiza-se um acoplamento entre os métodos de Monte Carlo, elementos finitos e procedimentos de otimização para considerar esses modos de falha importantes e classificá-los. Esse acoplamento também permite a redução do número de chamadas ao modelo de elementos finitos. Os cenários de falha são caracterizados como o encurtamento excessivo do concreto e o alongamento do aço. Estes cenários determinam a capacidade última da estrutura, e podem ser representados por um coeficiente escalar que multiplica todas as ações presentes na estrutura. Para a determinação desses estados estruturais últimos, um procedimento incremental-iterativo é utilizado. A análise de confiabilidade é realizada em diferentes conjuntos de realizações aleatórias das variáveis de projeto. O conjunto de respostas estruturais e de realizações permite a determinação dos coeficientes da superfície de respostas da estrutura. O acoplamento realizado permite também o tratamento com estruturas de concreto com elevado número de modos de falha. Aplicam-se as técnicas em exemplos de grelhas de concreto armado / In this work, new local approaches of reliability analysis applied to reinforced concrete grid structures are developed, taking into account several critical cross-section failure probabilities. Monte Carlo simulations are coupled with finite element analyses and optimization techniques with techniques to take into account the failure in the most important cross-sections, in order to classify the severity of failure modes. The failure scenario is depicted when either a concrete fiber or a steel bar reaches the predefined conventional limit. This scenario gives the structural ultimate capacity, which can be represented by a scalar coefficient multiplying all the loads acting on the structure. To achieve the failure scenario, an incremental and iterative procedure is used. To carry out the reliability analysis, the mechanical analysis has to be performed for different sets of random variable realizations of the mechanical, material and geometrical properties. The set of ultimate coefficients obtained from several mechanical analyses defines the response surface. The coupling between Monte Carlo simulations and response surface techniques applied in this work aims to reduce significantly the number of the finite element model calls, and hence to deal with real, or high-scale, reinforced concrete grids where large number of failure components can be found. The proposed procedure is then applied to reinforced concrete grids in order to show some more complex reinforced concrete examples