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Author: Christopher C. Pauly Publisher: ISBN: Category : Nature Languages : en Pages : 64
Book Description
The increasing acceptance and incorporation of fiber-reinforced polymer matrix composites (PMCs) as engineering construction materials have led many to look to the infrastructure as an application for these versatile materials. One such system is pultruded graphite fiber-reinforced epoxy (graphite/epoxy). Some PMC systems degrade when subjected to environmental conditions (e.g., moisture, stress, UV light, electrochemical polarization). These variables are typically studied either singularly or in series, but in real applications (e.g., aerospace, marine, infrastructure), these materials are subjected to many of these conditions simultaneously. To simulate field conditions, this study investigated the combined effects of an aqueous environment, electrochemical polarization, and applied bending stress on the durability of a pultruded graphite/epoxy composite. The findings indicate that graphite/epoxy composites cannot be assumed to be insensitive to degradation by environmental variables. Further, electrochemical polarization, as might occur with contact with a metal such as a fastener, can accelerate degradation. This damage requires the presence of moisture. Chloride and sulfate concentrations in rain are sufficient to establish an electrolyte within creviced regions, but deicing salts would overtake these as a contributor to conductivity. Further findings may be summarized as follows: 1.) Application of polarization in an aerated 0.6M NaCl environment led to breakdown of the fiber/matrix interface. The high pH environment created during the oxygen reduction reaction was necessary but not sufficient to create this breakdown, as the unpolarized specimen exposed to a pH 13 environment did not degrade. Cathodic polarization as would occur by coupling to steel or aluminum is required. 2.)Application of cathodic polarization did not significantly alter strength. Average measurements of shear strength, however, did decrease with the application of cathodic polarization for 70 and 90 days.
Author: Christopher C. Pauly Publisher: ISBN: Category : Nature Languages : en Pages : 64
Book Description
The increasing acceptance and incorporation of fiber-reinforced polymer matrix composites (PMCs) as engineering construction materials have led many to look to the infrastructure as an application for these versatile materials. One such system is pultruded graphite fiber-reinforced epoxy (graphite/epoxy). Some PMC systems degrade when subjected to environmental conditions (e.g., moisture, stress, UV light, electrochemical polarization). These variables are typically studied either singularly or in series, but in real applications (e.g., aerospace, marine, infrastructure), these materials are subjected to many of these conditions simultaneously. To simulate field conditions, this study investigated the combined effects of an aqueous environment, electrochemical polarization, and applied bending stress on the durability of a pultruded graphite/epoxy composite. The findings indicate that graphite/epoxy composites cannot be assumed to be insensitive to degradation by environmental variables. Further, electrochemical polarization, as might occur with contact with a metal such as a fastener, can accelerate degradation. This damage requires the presence of moisture. Chloride and sulfate concentrations in rain are sufficient to establish an electrolyte within creviced regions, but deicing salts would overtake these as a contributor to conductivity. Further findings may be summarized as follows: 1.) Application of polarization in an aerated 0.6M NaCl environment led to breakdown of the fiber/matrix interface. The high pH environment created during the oxygen reduction reaction was necessary but not sufficient to create this breakdown, as the unpolarized specimen exposed to a pH 13 environment did not degrade. Cathodic polarization as would occur by coupling to steel or aluminum is required. 2.)Application of cathodic polarization did not significantly alter strength. Average measurements of shear strength, however, did decrease with the application of cathodic polarization for 70 and 90 days.
Author: Defence Science and Technology Organisation Publisher: ISBN: Category : Airplanes Languages : en Pages : 18
Book Description
The long-term environmental durability of AS4/3501-6 graphite/epoxy composite was evaluated by a ground exposure trial conducted at four locations within Australia and one in Malaysia for a period of between 468 and 520 weeks. The combined effects of moisture uptake, UV degradation, temperature, rainfall and wind on the strength of the samples were all evaluated. The coupons absorbed an average of about 0.9% moisture by weight over the length of the trial. The residual strength of the coupons was determined using the interlaminar shear strength (ILSS) test (ASTM D2344) both at ambient temperature and 100 deg C.A statistical analysis of the results determined that the combined effect of moisture and elevated temperature (100 deg C) decreases ILSS by about 10%. A small enhancement in ILSS at room temperature was noted for specimens which absorbed moisture over the period of the trial. This is likely to be due to the combined effects of stress relief and plasticisation of the matrix. No other significant degradation mechanism was identified in this study apart from a slight decrease in ILSS of about 5% for specimens which were coated with the standard F/A-18 paint scheme. This may be attributed to the solvents used in the application of the paint However, the benefits of the paint protecting the composite surface from erosion and UV degradation far outweigh this structurally insignificant change in ILSS.
Author: Publisher: ISBN: Category : Languages : en Pages : 17
Book Description
An investigation has been completed which determines the physiochemical mechanisms of environmental durability and degradation of graphite-epoxy (Thornel T300 in 5208 epoxy) and fiber glass-epoxy S-2 glass in 5208 epoxy) under hydro-thermal (high moisture and temperature) exposure. Surface energy and moisture diffusion analysis provide nondestructive test methods which detect irreversible degradatiion of the fiber-matrix interface. Dynamic mechanical damping detects reversible volumetric plasticization effect on modulus, and the interlaminar shear strength and transfibrous fracture energy distributions. A composite durability characterization program is demonstrated which effectively combines preventative nondestructive evaluation (PNDE) with environmental failure and micromechanics analysis of composite structural reliability.
Author: R. J. Callinan Publisher: ISBN: 9780642116918 Category : Composite materials Languages : en Pages : 7
Book Description
With the increasing use of graphite/epoxy composites in aircraft primary structures to achieve weight and cost savings, the long term integrity of such structures is a matter of concern. In comparison with metals, it is known that the aerospace environment of temperature and moisture has a degrading influence on composites. This paper reviews the environmental effects on the static strength and fatigue life of graphite/epoxy composites.
Author: National Aeronautics and Space Administration (NASA) Publisher: Createspace Independent Publishing Platform ISBN: 9781725726598 Category : Languages : en Pages : 36
Book Description
The electrical conductivity of graphite epoxy composites can be substantially increased by intercalating (inserting guest atoms or molecules between the graphene planes) the graphite fibers before composite formation. The resulting high strength, low density, electrically conducting composites have been proposed for EMI shielding in spacecraft. Questions have been raised, however, about their durability in the space environment, especially with respect to outgassing of the intercalates, which are corrosive species such as bromine. To answer those concerns, six samples of bromine intercalated graphite epoxy composites were included in the third Evaluation of Oxygen Interaction with Materials (EOIM-3) experiment flown on the Space Shuttle Discovery (STS-46). Changes in electrical conductivity, optical reflectance, surface texture, and mass loss for SiO2 protected and unprotected samples were measured after being exposed to the LEO environment for 42 hours. SiO2 protected samples showed no degradation, verifying conventional protection strategies are applicable to bromine intercalated composites. The unprotected samples showed that bromine intercalation does not alter the degradation of graphite-epoxy composites. No bromine was detected to have been released by the fibers allaying fears that outgassing could be disruptive to the sensitive electronics the EMI shield is meant to protect. Gaier, James R. and Davidson, Michelle L. and Shively, Rhonda Glenn Research Center NASA-TM-107157, E-10100, NAS 1.15:107157 RTOP 233-1A-1E...
Author: Christopher C. Pauly
Author: Christopher C. Pauly
Author: Christopher Charles Pauly
Author: Defence Science and Technology Organisation
Author: 
Author: Sang Chel Kim
Author: R. J. Callinan
Author: Konstantinos Peimanidis
Author: Christian JL.
Author: Jack R. Vinson
Author: National Aeronautics and Space Administration (NASA)