In order to investigate the combined action of temperature, humidity, and ultraviolet (UV) radiation, polyphenylene sulfide (PPS)-carbon fiber composite specimens were exposed to environmental degradation through two different techniques: water immersion and UV climatic chamber. The moisture weight gain curves of the composites were compared with those of the neat matrix in order to determine the interface effect on moisture absorption. Fourier-transform infrared spectroscopy of UV-weathered samples presented oxidation formation. Compressive tests and dynamic mechanical thermal analysis (DMA) revealed that the weathered materials gained in stiffness, nevertheless a small deterioration in strength was found after long periods of UV radiation exposure.
Nowadays, the poly(phenylene sulfide) thermoplastic matrix composites have being utilized by most of the aerospace companies in order to replace a great quantity of the components made of aluminum, thermoset composites, or both and it is the reason they are being strongly considered to be utilized into marine structures, however, are quite often exposed to the environmental conditions that can damage them irreversibly, minimizing their qualities and compromising their performance. Depending on the aviation industry policy and requirements to learn more about these possible damages and increase the performance and the safety, this work aims to evaluate how the salt water and the UV light radiation conditioning affect the viscoelastic properties of the PPS/glass fiber laminates. Those viscoelastic experiments were performed by a DMA instrument before and after to submit the specimens to the conditioning and the experiments results were compared. Additionally, the moisture absorption mechanism after immersion in the artificial ocean solution and the material surface analysis after UV conditioning were investigated. According to the results found in this work, it can be concluded that the PPS/glass fiber absorbed approximately 0.3% of moisture into artificial ocean water conditioning under 60 C and this thermoplastic laminate exhibits moisture absorption according to the Fick's law, since the n constant experimental value was around 0.5.
In recent years, structural composites manufactured by carbon fiber/epoxy laminates have been employed in large scale in aircraft industries. These structures require high strength under severe temperature changes of -56° until 80 °C. Regarding this scenario, the aim of this research was to reproduce thermal stress in the laminate plate developed by temperature changes and tracking possible cumulative damages on the laminate using ultrasonic C-scan inspection. The evaluation was based on attenuation signals and the C-scan map of the composite plate. The carbon fiber/epoxy plain weave laminate underwent temperatures of -60° to 80 °C, kept during 10 minutes and repeated for 1000, 2000, 3000 and 4000 times. After 1000 cycles, the specimens were inspected by C-scanning. A few changes in the laminate were observed using the inspection methodology only in specimens cycled 3000 times, or so. According to the found results, the used temperature range did not present enough conditions to cumulative damage in this type of laminate, which is in agreement with the macro -and micromechanical theory.
Resumo: O contínuo crescimento na utilização de compósitos termoplásticos em componentes estruturais na indústria aeroespacial devese, 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 quando em serviço dessas estruturas. Componentes com 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. Em função do que foi exposto este trabalho tem como objetivo contribuir para a avaliação do efeito higrotérmico na resistência à fadiga do compósito termoplástico PPS/fibras de carbono. Os materiais estudados foram cedidos pela empresa holandesa TenCate, fornecedora de laminados da Airbus e EMBRAER. Os resultados obtidos neste trabalho mostram que compósitos de PPS/fibras de carbono apresentam um aumento nos valores de resistência à tração quando condicionados higrotermicamente, devido à plasticização desta matriz polimérica, aumentando, consecutivamente, sua tenacidade à fratura. Entretanto, a partir dos ensaios realizados, foi constatado que o condicionamento higrotérmico não alterou de forma significativa o comportamento de vida em fadiga dos laminados PPS-C. Palavras-chave: PPS, compósitos termoplásticos, propriedades mecânicas, fadiga. On the Analysis of Hygrothermal Effect on Fatigue Behavior of PPS/Carbon Fiber CompositeAbstract: The continued growth in the use of polymer composites in structural components in the aerospace industry is due primarily to the design flexibility, excellent mechanical properties and low density, combined with the high values of mechanical strength and stiffness and low incidence of corrosion, with which these structures meet several performance requirements when in service. Components with structural requirements may have their mechanical properties affected when exposed to harsh environments such as high temperature and humidity, and should be carefully evaluated before being put into service. The aim of the present work is to evaluate the hygrothermal effect on the fatigue resistance of thermoplastic PPS/carbon fiber composite. These laminates were obtained from TenCate Company, which provides composite laminates to Airbus and Embraer. PPS/carbon fibers composites exhibited increased tensile strength under hygrothermal conditioning due to plasticization of the polymer matrix, with the fracture toughness being also increased. In contrast, the hygrothermal conditioning did not alter significantly the behavior of fatigue life of laminates from PPS/carbon fiber composite.
The aim of this study was to investigate the effects of hygrothermal exposure, ultraviolet (UV) radiation, salt spray and thermal shock aging on the thermomechanical behavior of glass fiber reinforced by poly (ether-imide) (PEI) composites. Dynamic mechanical (DMA) and Thermomechanical (TMA) analyses have been performed on the aged PEI composites after being submitted to the climatic chambers. Additional techniques have been used to characterize the laminates, such as optical microscopy and infrared spectroscopy (FT-IR) in order to evaluate possible structural changes in these materials. Slight changes were observed both in glass transition temperature and in thermal expansion coefficient as a result from the environmental conditioning used (hygrothermal, salt spray, UV radiation and thermal shock conditioning). Thus, when exposed to these conditions, PEI/glass fiber laminates maintain its compromise with the performance component.
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