The objective of this research was to determine the effect of thermal cycling combined with mechanical loading on the development of microcracks in M40J/PMR-II- 50, the second generation aerospace application material. The objective was pursued by finding the critical controlling parameters for microcrack formation from mechanical stress-thermal cycling test. Three different in-plane strains (0%, 0.175~0.350%, and 0.325~0.650%) were applied to the composites by clamping composite specimens (M40J/PMR-II-50, [0,90]s, a unitape cross-ply) on the radial sides of half cylinders having two different radii (78.74mm and 37.96mm). Three different thermal loading experiments, 1) 23oC to –196oC to 250oC, 2) 23oC to 250oC, and 3) 23oC to -196oC, were performed as a function of mechanical inplane strain levels, heating rates, and number of thermal cycles. The apparatus generated cracks related to the in-plane stresses (or strains) on plies. The design and analysis concept of the synergistic stress-thermal cycling experiment was simplified to obtain main and interaction factors by applying 2k factorial design from the various factors affecting microcrack density of M40J/PMR-II-50. Observations indicate that the higher temperature portion of the cycle under load causes fiber/matrix interface failure. Subsequent exposure to higher stresses in the cryogenic temperature region results in composite matrix microcracking due to the additional stresses associated with the fiber-matrix thermal expansion mismatch.

No description available.

Experimental and numerical analyses were both adopted in the thesis. First, the BGA with three different solder ball components and pads, were investigated and their strength was affected by drop tests and thermal cycling test. Then the concept of numerical simulation to do the follow-up analysis was adopted. the relationships of stress, strain, and creep strain energy density were found. The lead-free solder ball has better resistance to the drop test with lower silver content; on the contrary, it has better properties due to thermal cycling tests with higher silver content. In the drop test, the failure of solder ball were found obviously in the packages that near four corner of the test board, and concentrated in the diagonal screw holes. The failure of solder ball was distributed over the peripheral of the package in the middle cross section of test board. Comparing the different position of 15 packages due to drop test, the amount of failed solder balls showed that the package positions U3, U8, U13 was obviously fractured, and the situation of fracture was relatively slight in the positions of U1, U5, U6, U7, U9, U10, U11, U15. In the fatigue life prediction of thermal cycling test, the simplified model of package in 45¢X direction was mostly close to the experimental data. After the except ion of the solder ball with failure mode A1, the major failure mode in drop test was mode B3. But the mode C was the majority of thermal cycling test. The structure and intensity of SMD play an important role on above experiments; the better choice of SMD can reduce the rate of failure mode A1, and improve the accuracy of the experiment.

The Plastic Ball Grid Array (PBGA) package and flip-chip technology have been widely used in the microelectronics industry. However, due to the effect of hygroscopic and thermal stresses, the reliability is still of concern during manufacturing and operation, especially for the thermal-mechanical behavior of its corresponding interfaces. Influences of the storage conditions and reflow parameters on the warpage of the PBGA package are investigated in this study first. As the results, the warpage reflected the interaction of the extent of moisture absorption and the change in reflow parameters significantly. Furthermore, a critical relative moisture absorption between 0.25% and 0.30% is found for a considerable warpage response. Next, this study presents an experimental investigation of the adhesion strength of epoxy-based encapsulant material to solder mask coated FR-4 substrate under thermal cycling. Effects of the number of thermal cycles on the interfacial strength are investigated by using button shear test. The relationship between the interfacial strength and thickness of solder mask is also examined. Moreover, to characterize the degradation and fracture behavior, the morphologies of fractured surfaces of the test specimens are analyzed by scanning electron microscopy. The results of this experiment show that the interfacial strength of the epoxy-based encapsulant/solder mask/substrate joint is apparently reduced by thermal fatigue. And, the test specimen with larger solder mask thickness has higher interfacial strength. Finally, the single-lap joint test, nonlinear finite element analysis and Moiré interferometry are employed to obtain strain/stress distributions on the interface of solder mask and substrate. The effects of solder mask thickness and overlap length are then determined, separately. The results of this study can afford important information for characterizing the features of moisture absorption, warpage and interfacial adhesion of PBGA packages. Furthermore, it can be helpful to identify improvements required in reliability of the package design.

The effects of different ferrule length and epoxy layer thickness of the module of optical fiber connector under thermal cycling are investigated in this thesis. The finite element method package, MSC. MARC, is used in this study and the coupled thermal-elastic-plastic model is employed in the analysis. The mechanical behavior and life prediction with different length of ferrule and thickness of epoxy layer are considered. It is shown that the thickness of epoxy layer has the major effect on the life of the module. The stress and strain in the fiber and epoxy layer are decreasing with increasing of ferrule length, and the life of the module is increasing with increasing of thickness of epoxy layer. Finally, we recommend the ferrule length can be designed between 7.89mm ~10.5mm.

The variations of residual stress distributions on solder balls under the cyclic thermal load and aging processes are investigated in this thesis. The solidification phenomena for different shapes and materials of the solder balls during the reflow process are predicted by using the Surface Evolver program. The distribution of residual stress in the solder ball is calculated by employing the MARC finite element package. The temperature dependent material properties of the solders, i.e. 63Sn/37Pb and 96.5Sn/3.5Ag, are used in the residual stresses calculations. The variation of the residual stresses distributions of different solder balls under the temperature cycling test ( between ¡V40¢J and 85¢J ) and the aging test ( at 85¢J ) are simulated and studied. The effects of the solder parameters, i.e. the solder height and the pad geometry shapes on the residual stresses distribution are also studied. Besides, the same simulation and analysis has also applied on the solder ball with an unleaded solder 96.5Sn/3.5Ag. A better understanding about the variation of the residual stress in a solder ball is expected from this analysis.

Abstract The effects of residual stresses distribution and post-weld-shift on the signal coupling efficiency of an Optical Add & Drop Multiplex (OADM) are investigated in this thesis. The position variations between the two collimators in the OADM under the temperature cycling test and high temperature aging test have been simulated and studied. The finite element method package, i.e. MARC, is used for the stresses and deformation simulations of an OADM under different load cases. The coupled thermal-elastic-plastic model is employed in the analysis, and the creep effect of the solder is considered in the numerical simulations. The temperature dependent material properties of the 63Sn/37Pb and 96.5Sn/3.5Ag solder are used for the solder solidification, temperature cycling and aging tests. The effects of the OADM packaging parameters, i.e. the different offset angles between collimators, different solder are also studied. Besides, the same simulation and analysis has also applied on the soldering with and without cavity. A comparison between the simulated and measured results indicates that the proposed finite element model is feasible for analyzing the OADM packaging problems.

Corrosion in underground and submerged steel pipes is a global problem. Coatings serve as an impermeable barrier or a sacrificial element to the transport of corrosive fluids. When this barrier fails, corrosion in the metal initiates. There is a critical need for sensors at the metal/coating interface as an early alert system. Current options utilize metal sensors, leading to accelerating corrosion. In this dissertation, a non-conductive sensor textile as a viable solution was investigated. For this purpose, non-woven zinc (II) oxide-polyvinylidene fluoride (ZnO-PVDF) nanocomposite fiber textiles were prepared in a range of weight fractions (1%, 3%, and 5% ZnO) and placed at the coating/steel interface. Electrochemical impedance spectroscopy (EIS) testing was performed during the immersion of the coated samples to validate the effectiveness of the sensor textile. In the second part of this dissertation, an accelerated thermal cyclic method has been applied to determine sensor's reliability in detecting corrosion under actual service condition. The results suggested that the coating is capable of detecting corrosion under harsh conditions. Moreover, the addition of ZnO decreases the error in sensor textile and improved coating's barrier property. In the next phase, experiments were conducted to detect the type of corrosion (pitting or uniform) underneath the protective coating as it has profound effect on overall performance and durability of the steel pipe. The data suggested that the pitting corrosion drew a lot of current, hence its resistance was significantly low which was tacked by the sensor accurately whereas the uniformly corroded specimens showed almost identical results which portrayed the sensor's ability to detect pitting corrosion.

Recent trends to miniaturized systems such as smartphones and wearables, as well as the rise of autonomous vehicles relying on all-electric and smart in-car systems, have brought unprecedented needs for superior performance, functionality, and cost requirements. Transistor scaling alone cannot meet these metrics unless the remaining system components such as substrates and interconnections are scaled down to bridge the gap between transistor and system scaling. In this regard, 3D glass system packages have emerged as a promising alternative due to their ultra-short system interconnection lengths, higher component densities and system reliability enabled by the tailorable coefficient of thermal expansion (CTE), high dimensional stability and surface smoothness, outstanding electrical properties and low-cost panel-level processability of glass. The research objectives are to demonstrate board-level reliability of large, thin, glass packages directly mounted on PCB with conventional BGAs at pitches of 400µm SMT and smaller. Two key innovations are introduced to accomplish the objectives: a.) Reworkable circumferential polymer collars providing strain-relief at critical high stress concentration areas in the solder joints, b.) novel Mn-doped SACMTM solder to provide superior drop test performance without degrading thermomechanical reliability. Modeling, package and board design, fabrication and reliability characterization were carried out to demonstrate reliable board-level interconnections of large, ultra-thin glass packages. Finite-element modeling (FEM) was used to investigate the effectiveness of circumferential polymer collars as a strain-relief solution on fatigue performance. Experimental results with polymer collars indicated a 2X improvement in drop performance and 30% improvement in fatigue life. Failure analysis was performed using characterization techniques such as confocal surface acoustic microscopy (C-SAM), optical microscopy, X-ray imaging, and scanning electron microscopy/energy dispersive spectrometry (SEM/EDS). Model-to-experiment correlation was performed to validate the effectiveness of polymer collars as a strain-relief mechanism. Enhancement in board-level reliability performance with advances in solder materials based on Mn-doped SACMTM is demonstrated in the last part of the thesis.The studies, thus, demonstrate material, design and process innovations for package-to-board interconnection reliability with ultra-thin, large glass packages.

O acelerado e freqüente desenvolvimento de novos materiais e técnicas restauradoras tornam necessárias avaliações rápidas que estimem seus desempenhos clínicos. Este estudo avaliou protocolos de envelhecimento acelerado, in vitro, capazes de simular o desempenho de restaurações adesivas frente aos desafios inerentes ao ambiente oral. Foram utilizados 36 molares hígidos, cortados ao meio e divididos aleatoriamente em 12 grupos. Em todos os grupos foi realizada a exposição da superfície dentinária, delimitação da área de adesão e condicionamento ácido da superfície, seguida a aplicação do Sistema Adesivo Scotchbond Multiuso, e colocação da resina composta Z100, em incrementos. Foram confeccionados 6 grupos em formato de palito e 6 grupos em formato de haltere: dois grupos não foram submetidos à ciclagem térmica e mecânica (STSM-P e STSM-H); outros dois foram submetidos à ciclagem térmica (1.000 ciclos; 5-55ºC; 1min em cada banho) e não a mecânica (CTSM-P e CTSM-H); dois ainda foram submetidos à ciclagem mecânica com dispositivo Nova Ética e não a térmica (STNE-P e STNE-H); dois foram submetido à ciclagem mecânica com dispositivo Nova Ética (500.000 ciclos), acrescido de ciclagem térmica (CTNE-P e CTNE-H); outros dois por fim, foram submetidos à ciclagem mecânica por Microrotação (105 ciclos, aproximadamente por 7 horas), e não a térmica (STMR-P e STMR-H); por fim os dois últimos grupos foram submetido à ciclagem mecânica por Microrotação acrescido de ciclagem térmica (CTMR-P e CTMR-H). Todos os grupos foram preparados para teste de microtração. Com as medidas de resistência de união dos palitos e halteres de cada dente foi realizada análise de variância e teste de Tukey. A interação tripla Formato -FORM- (Palito ou haltere) X Ciclagem Térmica- T- (Com e Sem) X Ciclagem Mecânica-M- (Nova Ética e Microrotação) não foi significante (p=0,698), bem como a interação 2 a 2 dos mesmos fatores: FORMxT (p=0,391); TxM (p=0,477); FORM x M (p=0,746). O fator Formato do espécime (Palito ou Haltere) teve diferença extremamente significante (p=0,000), sendo que os valores dos halteres foram maiores que os dos palitos. O fator Ciclagem Térmica (Com e Sem) não foi estatisticamente significante (p=0,2), bem como o fator Ciclagem Mecânica (Nova Ética e Microrotação) (p=0,587). Pode-se concluir que: a ciclagem térmica, bem como as ciclagens mecânicas sistema Nova Ética e Microrotação não foram capazes de reduzir significativamente os valores de resistência de união das interfaces adesivas, nem quando aplicadas isoladamente, nem quando associadas; os espécimes com formato de palito apresentaram valores de resistência de união menores do que os em formato de haltere; não foi possível estabelecer nenhum padrão de degradação entre os grupos através da microscopia eletrônica de varredura; os elementos finitos identificaram uma distribuição mais homogênea das tensões geradas na interface dos espécimes em formato de haltere. / The rapid and frequent development of new materials and restorative techniques necessitate rapid assessments to estimate their clinical outcomes. This study sought to evaluate protocols for accelerated aging, in vitro, capable of simulating the performance of adhesive restorations with challenges inherent to the oral environment. The study included 36 molars that were randomly divided into 12 groups. In all groups were exposed dentin surface, defining the area of adhesion and etching the surface, then the application of Scotchbond Multipurpose Adhesive System, and placement of composite resin Z100, in increments. Six groups were fabricated in the shape of sticks and six other groups in dumbbell shape: the first was not subjected to thermal cycling and mechanical (STSM-P and STSM-H), the second was subjected to thermal cycling (10,000 cycles, 5-55 ° C) and not the mechanics (CTSM-P and CTSM-H); the third was subjected to mechanical cycling device with new Ethics (500,000 cycles) and not thermal (STNE-P and STNE-H); the fourth was subjected to mechanical cycling device with new Ethics, plus thermal cycling (CTNE-P and CTNE-H); the fifth was submitted the mechanical cycling device for Microrotation (105 cycles), but not thermal (STMR-P and STMR-H) and finally the sixth was subjected to mechanical cycling device for Microrotation plus thermal cycling (CTMR-P and CTMR-H). All groups were prepared for microtensile bond-strength test. With the measures of bond strength of each tooth was performed statistical analysis (ANOVA and Tukey test). Random samples of specimens were evaluated by SEM. The triple interaction format (stick or dumbbell-shaped) X Thermal cycling (with and without) X Cycling Mechanics (New Ethics and Microrotation) was not significant (p = 0.698), as well as the interaction 2-2 of the same factors: FORMXT (p = 0.391); TXM (p = 0.477); FORMxM (p = 0.746). With regard to factor Format specimen is observed that the bond strength values obtained for the dumbbell-shaped are higher than those obtained for the sticks (p = 0.000). With regard to factor Thermal cycling was observed that the difference was not statistically significant (p = 0.2). As for factor Cycling Mechanics, the values of groups without cycling were very similar to those obtained in groups cycled through the system New Ethics, and the system by Microrotation, no significant difference between any of them (p = 0.587). The conclusions were that the stick-shaped specimens showed values of bond strength lower than the dumbbell-shaped; thermocycling and mechanical cycling were not able to significantly reduce the values of bond strength of adhesive interfaces, even when applied alone or when associated. It could not be establish any pattern of degradation among the groups by SEM; the finite element identified a more homogeneous distribution of stresses generated at the interface of dumbbell shaped specimens.