The main objective of this work was to develop a framework to predict the fracture toughness degradation of highly toughened adhesive joints using fracture test data obtained by accelerated open-faced degradation method. First, the mixed-mode fracture resistance (R-curve) behavior of two rubber-toughened epoxy-aluminum adhesive systems was measured and could be fit in a bilinear R-curve model. Then, open-faced DCB (ODCB) specimens of the same adhesive systems were aged over a relatively wide range of temperature, relative humidity (RH) and time, dried and tested to characterize the irreversible evolution of the mixed-mode fracture R-curves. The R-curve bilinear model parameters of adhesive system 1 varied significantly with degradation while that of adhesive system 2 remained unchanged. The absorption and desorption of water in the adhesives cast wafers was measured gravimetrically. The absorption data were fitted to a new sequential dual Fickian (SDF) model while water desorption was modeled accurately using Fick’s law. A significant difference was observed between the amounts of retained water in the two adhesives after drying. An exposure index (EI) was defined as the integral of water concentration over time and calculated at all points in the ODCB and closed DCB joints. The fracture toughness of the closed joints was then predicted from these calculated EIs by making reference to fracture toughness data from the ODCB specimens degraded to various EI levels. To verify the predictions, fracture experiments and analyses were carried out for closed DCB joints. Good agreement was found between the predicted and experimentally measured fracture toughness values for the degraded closed DCB joints. Furthermore, the crack path and fracture surface characteristics were evaluated as a function of the degree of aging using optical profilometery. The unexpected crack path in the mixed-mode fracture of unaged open-faced DCB specimens was addressed. The results showed a strong relationship between fracture surface parameters and the critical strain energy release rate, Gcs, irrespective of the type of adhesive and exposure condition.

The main objective of this work was to develop a framework to predict the fracture toughness degradation of highly toughened adhesive joints using fracture test data obtained by accelerated open-faced degradation method. First, the mixed-mode fracture resistance (R-curve) behavior of two rubber-toughened epoxy-aluminum adhesive systems was measured and could be fit in a bilinear R-curve model. Then, open-faced DCB (ODCB) specimens of the same adhesive systems were aged over a relatively wide range of temperature, relative humidity (RH) and time, dried and tested to characterize the irreversible evolution of the mixed-mode fracture R-curves. The R-curve bilinear model parameters of adhesive system 1 varied significantly with degradation while that of adhesive system 2 remained unchanged. The absorption and desorption of water in the adhesives cast wafers was measured gravimetrically. The absorption data were fitted to a new sequential dual Fickian (SDF) model while water desorption was modeled accurately using Fick’s law. A significant difference was observed between the amounts of retained water in the two adhesives after drying. An exposure index (EI) was defined as the integral of water concentration over time and calculated at all points in the ODCB and closed DCB joints. The fracture toughness of the closed joints was then predicted from these calculated EIs by making reference to fracture toughness data from the ODCB specimens degraded to various EI levels. To verify the predictions, fracture experiments and analyses were carried out for closed DCB joints. Good agreement was found between the predicted and experimentally measured fracture toughness values for the degraded closed DCB joints. Furthermore, the crack path and fracture surface characteristics were evaluated as a function of the degree of aging using optical profilometery. The unexpected crack path in the mixed-mode fracture of unaged open-faced DCB specimens was addressed. The results showed a strong relationship between fracture surface parameters and the critical strain energy release rate, Gcs, irrespective of the type of adhesive and exposure condition.

Made available in DSpace on 2014-06-11T19:29:53Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-09-26Bitstream added on 2014-06-13T18:59:49Z : No. of bitstreams: 1 faria_mcm_me_guara.pdf: 1588754 bytes, checksum: 9b1c6339bf770de5c7936e9e915a4c01 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O contínuo crescimento na utilização de compósitos termoplásticos em componentes estruturais na indústria aeroespacial deve-se, primordialmente, à flexibilidade de projeto, excelência de suas propriedades mecânicas e baixa massa específica, aliadas aos elevados valores de resistência mecânica e rigidez e baixa incidência de corrosão, atendendo aos severos requisitos de desempenho dessas estruturas quando em serviço. No entanto, componentes que requerem exigências estruturais, quando expostos a ambientes agressivos como elevada temperatura e umidade, podem ter suas propriedades mecânicas sensibilizadas por esses fatores ambientais, e devem ser cuidadosamente avaliados antes de serem colocados em serviço. Sendo assim, o objetivo deste trabalho é avaliar a influência do condicionamento higrotérmico (câmara climática e imersão em banho termostatizado) nas propriedades mecânicas (resistências à tração, fadiga e cisalhamento) e viscoelásticas de laminados PPS/Carbono e PPS/Vidro. Os laminados utilizados neste trabalho foram fornecidos pela empresa holandesa TenCate. Os resultados mostram que os laminados condicionados em câmara climática apresentaram absorção de umidade segundo as leis de Fick, entretanto, os laminados de PPS/Vidro submetidos ao condicionamento por imersão em banho termostatizado apresentaram um comportamento anômalo. Associado a estes resultados foi também observado que os laminados condicionados tiveram um decréscimo no valor de suas resistências ao cisalhamento, entretanto, apresentaram um aumento nos valores de temperatura de transição vítrea e resistência à tração. Os resultados obtidos a partir dos ensaios de fadiga praticamente não sofreram alteração com o condicionamento ambiental. A partir dos resultados obtidos neste trabalho, pode ser concluído que a utilização de laminados de PPS/Carbono e PPS/Vidro em aplicações... / The continuous use of thermoplastic composites in structural components of aerospace industry is due to essentially to the project flexibility, good mechanical properties and low specific mass, allied with elevated values of mechanical strength and rigidity and low corrosion incidence, attempted to severe requirements of these structures in service. However, components that require structural demand, when exposed in aggressive atmosphere such as high temperature and moisture, can have mechanical properties sensibility for these factors, and should be carefully studied before to be available in service. This way, the purpose of this work is to evaluate the hygrothermal conditioning influence (by using hygrothermal chamber and thermostatic bath immersion) on the mechanical properties (tensile strength fatigue and interlaminar shear) and on the viscoelastic behavior of PPS/carbon and PPS/glass laminates. The laminates used in this work were supplied by TenCate Dutch Company. The results obtained shows that conditioning laminates in hygrothermal chamber presented moisture absorption according to the Fick‟s law, however, the PPS/glass laminates submitted to thermostatic bath immersion presented a anomalous behavior. Associated to these results, it was also observed that the conditioned laminates had a decrease of shear strength values, however, presented an increase of glass transition temperature and tensile strength values. Results obtained according to fatigue tests practically do not change with the atmosphere conditioning. According to the results obtained in this work can be concluded that the use of thermoplastic laminates in aerospace applications is viable, because these laminates are less susceptible to atmosphere effect problems.

Thermal resistance per unit thickness for Vacuum Insulation Panel (VIP) is 5 to 10 times higher than conventional insulation materials. This makes VIP an attractive option for retrofitting exterior building envelopes. Insulation can be added in an exterior wall either on the interior side, exterior side or in the available stud cavity. VIP has high vapor diffusion resistance factor and could lead to moisture management risk in the wall layers because of the steep temperature gradient in the wall generated due to very high thermal resistance of VIP. VIP is a relatively new insulation material for building envelope construction, thus the hygrothermal or moisture management performance of VIP-insulated exterior building envelopes need to be critically analyzed before its application. This study aims to evaluate the moisture management risk associated with wood-frame stucco-cladded exterior walls retrofitted with VIP using a 2-D hygrothermal simulation tool WUFI-2D. Eight North American locations were considered, based on Moisture Index (MI) which varied between 0.13 and 1.17, and two different indoor hygrothermal loading conditions as prescribed by the ASHRAE 160P and EN 13788, respectively. The outputs from hygrothermal simulations (water content, relative humidity and temperature) were critically analysed and expressed further using freeze-thaw cycles and RHT indices. The results show that the appropriately designed VIP retrofitted walls can have superior moisture management performance as compared to conventional stucco-cladded wall. / Graduate

In this dissertation, the effect of temperature and humidity on the viscoelastic and fracture properties of proton exchange membranes (PEM) used in fuel cell applications was studied. Understanding and accurately modeling the linear and nonlinear viscoelastic constitutive properties of a PEM are important for making hygrothermal stress predictions in the cyclic temperature and humidity environment of operating fuel cells. In this study, Nafion® NRE 211, Gore-Select® 57, and Ion Power® N111-IP were characterized under various humidity and temperature conditions. These membranes were subjected to a nominal strain in a dynamic mechanical analyzer (DMA), and their stress relaxation behavior was characterized over a period of time. Hygral master curves were constructed noting hygral shift factors, followed by thermal shifts to construct a hygrothermal master curve. This process was reversed (thermal shifts followed by hygral shifts) and was seen to yield a similar hygrothermal master curve. Longer term stress relaxation tests were conducted to validate the hygrothermal master curve. The Prony series coefficients determined based on the hygrothermal stress relaxation master curves were utilized in a linear viscoelastic stress model. The nonlinear viscoelastic behavior of the membranes was characterized by conducting creep tests on uniaxial tensile specimens at various constant stress conditions and evaluating the resulting isochronal stress-strain plots. The nonlinearity was found to be induced at relatively moderate stress/strain levels under dry conditions. To capture the nonlinearity, the well known Schapery model was used. To calculate the nonlinear parameters defined in the Schapery model, creep/recovery tests at various stress levels and temperatures were performed. A one-dimensional Schapery model was developed and then validated using various experiments. The fracture properties were studied by cutting membranes using a sharp knife mounted on a specially designed fixture. Again, various temperature and humidity conditions were used, and the fracture energy of the membranes was recorded as a function of cutting rate. Fracture energy master curves with respect to reduced cutting rates were constructed to get some idea about the intrinsic fracture energy of the membrane. The shift factors obtained from the fracture tests were found to match with those obtained from the stress relaxation experiments, suggesting that the knife cutting process is viscoelastic in nature. The rate and temperature dependence for these fracture energies are consistent with the rate, temperature, and moisture dependence of the relaxation modulus, suggesting the usefulness of a viscoelastic framework for examining and modeling durability of fuel cell membranes. The intrinsic fracture energy was initially thought to be a differentiating factor, which would separate various membranes tested in this study from one another. However, it was later found that all the membranes tested showed similar values at lower cutting rates, but showed significant variation at higher reduced cutting rates, and thus was thought to be a more meaningful region to differentiate the membranes for durability understanding. While the preceding work was undertaken to characterize as-received commercial PEMs, it is possible to modify material properties through treatment processes including thermal annealing and water treatment. The transient and dynamic viscoelastic properties of water-treated Nafion membranes revealed unusual behavior. Such unusual properties might have originated from irreversible morphological changes in PEM. Besides the constitutive viscoelastic properties, another set of properties useful for the stress modeling is the hygral strain induced as a function of relative humidity (RH) The effect of pretreatment on hygral strains induced as a function of RH was also investigated. These studies suggest that pretreatment significantly changes the mechanical properties of proton exchange membranes. / Ph. D.

L'objectif de notre étude est de mettre en évidence les synergies existantes entre les différents facteurs de vieillissement lors de la dégradation d’un revêtement polymère modèle, représentatif d’une peinture anticorrosion.Notre travail a consisté à suivre le vieillissement hygrothermique du système DGEBA/TETA sous forme de film libre et de revêtement déposé sur substrat acier dans différentes solutions (eau pure et NaCl 3%) pour différentes températures et contraintes mécaniques visco-élastique appliquées. Nos résultats ont montré que le programme de cuisson affectait les propriétés physico-chimiques et mécaniques du système initial et que l’absorption d’eau, non homogène, suivait une loi non-Fickienne, suite à un phénomène de gonflement.La prise en eau et la diffusion ont été caractérisées par gravimétrie et spectroscopie d’impédance électrochimique. Nos résultats montrent que les propriétés barrière du revêtement diminuent avec la quantité d’eau absorbée et avec la température de vieillissement. Cependant, la contrainte plane appliquée sur le système tend à contrarier cet effet. La formalisation de nos observations expérimentales dans le cadre d’une approche thermodynamique a montré l’effet prépondérant de la partie entropique par rapport à la partie enthalpique de l’énergie d’activation des processus de transport de l’eau, en raison de l’orientation des chaînes sous l’action de la contrainte. De plus, une diminution de la permittivité relative du revêtement sec a été observée en fonction de la température et de la contrainte appliquée, indépendamment de son signe (tension ou compression). Dans ce cas, la contribution enthalpique semble être prépondérante. / The objective of this study is to highlight synergies existing between different ageing factors during the degradation of a polymer model coating system, representing an anti-corrosion coating.We first monitored the hygrothermal ageing of DGEBA/TETA system as free films and as attached films onto a steel substrate in different solutions (water and NaCl 3wt% solution) for different temperatures and applied mechanical visco-elastic stresses. Our results showed that the curing programs affected the physic-chemical and mechanical properties of the cured systems and that the non-homogeneous water uptake process followed a non-Fickian law, due to a swelling phenomenon.The water uptake and diffusion were characterized by gravimetry and electrochemical impedance spectroscopy. The results indicate that the barrier properties of the coating decrease with the quantity of absorbed water in system and with the increasing of the ageing temperature. However, the planar stress applied onto the system tends to counteract this effect. The formalization of our experimental observations within a thermodynamic approach showed the predominant effect of the entropic part in comparison with enthalpic part of the activation energy of the water uptake process, due to the reorientation of polymer chains under the applied stress. In addition, a decrease in the relative permittivity of the initial dry coating was observed as a function of the temperature and the applied stress, regardless of its sign (tension and compression). In this case, the enthalpic contribution seems to be predominant.

This study focuses on the hygrothermal performance of Moso bamboo. The knowledge in this aspect is remarkable important for the research of building energy saving and the low carbon building design. However, the detailed hygrothermal properties of Moso bamboo are fairly rare. To obtain these data, a series of experimental works have been done for measurement of density, porosity, thermal conductivity, specific heat capacity, water vapour permeability, hygrothermal expansion and sorption isotherm of Moso bamboo. To obtain further understanding on the hygrothermal performance of Moso bamboo, a number of dynamic heat and moisture transfer experiments were conducted. These experiments simulated two extreme outdoor environments and one indoor environment. The temperature and RH responses of Moso bamboo panels were monitored. Then a coupled transient heat and moisture transfer numerical simulation at the material level was conducted to predict and validate the hygrothermal performance of Moso bamboo. A sensitivity study of the hygrothermal properties of bamboo was also presented to indentify the influence of each hygrothermal property of Moso bamboo. Major findings include the following aspects. Both experiment and simulation results appear to be consistent with the results of measurements of the basic hygrothermal parameters. The parametric study found that density can be regarded as the most sensible parameter to influence the temperature simulation results at the transient state, while the thermal conductivity dominated the temperature variation at the steady state. The water vapour diffusion resistance factor can be regarded as the most critical parameter to influence the RH simulation results. The influence of liquid water diffusivity is negligible in this study. The parametric study results indicated that the simulation with moisture is more accurate than the simulation without moisture in both equilibrium and transient state. The results also imply that the existence of moisture could increase the heat capacity and reduce the thermal conductivity. The results of this study recommend that the external part of the bamboo culm wall can be utilised to minimise the RH variation of the panel while the internal part of the bamboo culm wall is suitable to increase the thermal insulation performance of the panel. To avoid hygroexpansion, the implementation of external part of bamboo culm wall needs to be minimised.

This thesis examines the widespread moisture problems which emerged over the past twenty years in buildings throughout coastal British Columbia, commonly known as ‘leaky condos’. A literature review of building physics and a historical review of wood-frame construction in North America provide background for this review. The purpose of this work is to report and interpret the performance of rainscreen walls in the coastal climate of Vancouver BC, based on extensive field data from five local buildings constructed or rehabilitated with rainscreen wall assemblies. Hygrothermal data was collected within exterior walls, and corresponding environmental data was recorded for each building. Driving rain loads at the five buildings across the city are calculated and compared to Vancouver airport data. Site factors are shown to have a significant impact on driving rain load, wind speed and direction. The WUFI 4.1 hygrothermal model was compared with the field data collected and found to be accurate at predicting past performance. Applying this validated model to each wall assembly, further simulations were performed to determine the impact of boundary conditions and assembly details on wall performance. Field measurements and modeling show that ventilated and drained claddings (i.e. rainscreen) reduce the sensitivity of wood frame buildings to moisture damage. Ventilation of the cladding is shown to be particularly important and natural buoyancy forces (from temperature and humidity differences between cavity and exterior) are usually sufficient to provide good drying. Exterior insulation is shown to further improve rainscreen wall performance by increasing the drying potential of the sheathing to both the exterior and interior. Additional work performed included material testing of fiberglass-faced gypsum sheathing and air-leakage testing of individual suites in the monitored buildings. Elevated interior humidity, resulting from inadequate ventilation, is shown to be exacerbated by inter-zonal air-flow in multi-unit residential buildings.

Roofs are the single enclosure element common to artificial shelters constructed by all cultures in all climate regions. The hygrothermal performance of insulated, sloped, wood-framed roof assemblies has long been of interest to building scientists and building codes alike. Requirements for the ventilation of roof assemblies have been included in building codes for more than 50 years, however moisture problems still occur. Unvented roof assemblies have been suggested as an alternate and potentially superior solution. While unvented roofs have become relatively common in the warmer southern climates of North America, some technical issues remain unclear and the need exists for further study and demonstration of the hygrothermal performance of both ventilated and unvented roof assemblies in cold northern climates. This thesis seeks to address these issues through a review of existing literature, experience and industry practice, field investigation and measurement, analytical calculation and computer simulations.

This thesis examines the widespread moisture problems which emerged over the past twenty years in buildings throughout coastal British Columbia, commonly known as ‘leaky condos’. A literature review of building physics and a historical review of wood-frame construction in North America provide background for this review. The purpose of this work is to report and interpret the performance of rainscreen walls in the coastal climate of Vancouver BC, based on extensive field data from five local buildings constructed or rehabilitated with rainscreen wall assemblies. Hygrothermal data was collected within exterior walls, and corresponding environmental data was recorded for each building. Driving rain loads at the five buildings across the city are calculated and compared to Vancouver airport data. Site factors are shown to have a significant impact on driving rain load, wind speed and direction. The WUFI 4.1 hygrothermal model was compared with the field data collected and found to be accurate at predicting past performance. Applying this validated model to each wall assembly, further simulations were performed to determine the impact of boundary conditions and assembly details on wall performance. Field measurements and modeling show that ventilated and drained claddings (i.e. rainscreen) reduce the sensitivity of wood frame buildings to moisture damage. Ventilation of the cladding is shown to be particularly important and natural buoyancy forces (from temperature and humidity differences between cavity and exterior) are usually sufficient to provide good drying. Exterior insulation is shown to further improve rainscreen wall performance by increasing the drying potential of the sheathing to both the exterior and interior. Additional work performed included material testing of fiberglass-faced gypsum sheathing and air-leakage testing of individual suites in the monitored buildings. Elevated interior humidity, resulting from inadequate ventilation, is shown to be exacerbated by inter-zonal air-flow in multi-unit residential buildings.