Effects of Thermal Cycling Environment on Graphite/Epoxy Composites PDF Download
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Author: JL. Camahort
Publisher:
ISBN:
Category : Coefficient of thermal expansion
Languages : en
Pages : 13
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Book Description
Graphite/epoxy (Gr/E) composites have attractive properties--low density, high stiffness, and a low coefficient of thermal expansion (CTE)--that make them prime candidates for many spacecraft applications. The effects of a thermal cycling environment on the dimensional stability and microstructural integrity of Gr/E composites were evaluated. Severe microcracking was found in several high-modulus fiber (HMS)-reinforced 350°F-cure epoxy resin systems after exposure to 25 thermal cycles between the temperature of liquid nitrogen (-320°F) and that of boiling water (+212°F). A hybrid system combining Thornel-300 (T-300) fabric and HMS tape exhibited fewer microcracks, with the fabric acting as a crack stopper. Of the material systems investigated, a 250°F-cure system, HMS/CE 339, was found to be the most resistant to microcracking. The effects of thermal cycling on the microyield strength (MYS) and CTE of several near-zero expansion Gr/E composites were also studied.
Author: JL. Camahort
Publisher:
ISBN:
Category : Coefficient of thermal expansion
Languages : en
Pages : 13
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Book Description
Graphite/epoxy (Gr/E) composites have attractive properties--low density, high stiffness, and a low coefficient of thermal expansion (CTE)--that make them prime candidates for many spacecraft applications. The effects of a thermal cycling environment on the dimensional stability and microstructural integrity of Gr/E composites were evaluated. Severe microcracking was found in several high-modulus fiber (HMS)-reinforced 350°F-cure epoxy resin systems after exposure to 25 thermal cycles between the temperature of liquid nitrogen (-320°F) and that of boiling water (+212°F). A hybrid system combining Thornel-300 (T-300) fabric and HMS tape exhibited fewer microcracks, with the fabric acting as a crack stopper. Of the material systems investigated, a 250°F-cure system, HMS/CE 339, was found to be the most resistant to microcracking. The effects of thermal cycling on the microyield strength (MYS) and CTE of several near-zero expansion Gr/E composites were also studied.
Author: VF. Mazzio
Publisher:
ISBN:
Category : Carbon fibers
Languages : en
Pages : 15
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Book Description
There is strong evidence that weaker composites, regardless of fiber content, tend to cleave on a single plane, while stronger specimens exhibit extensive fracture zones as a result of cumulative damage. This type of behavior is the same before and after thermal cycling of specimens up to 500 cycles.
Author: Joseph Kwaku Mensah
Publisher:
ISBN:
Category :
Languages : en
Pages : 96
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Book Description
Author: Christian JL.
Publisher: ASTM International
ISBN:
Category :
Languages : en
Pages : 105
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Book Description
Author: N. Jayaraman
Publisher:
ISBN:
Category : Composite materials
Languages : en
Pages : 15
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Book Description
Graphite-fiber-reinforced polymer composite materials have become prime candidates for space structures. The high specific strengths and stiffnesses obtainable with these materials and the ability to design them with a near-zero coefficient of thermal expansion provide a flexibility that is virtually unmatched. However, microcracks resulting from thermal cycling can lead to drastic property changes of the composites. Specimens of five composite materials, each with the same epoxy-cyanate blend matrix and reinforced with different graphite fibers, were subjected to a simulated spacecraft thermal cycling environment to determine the effects of fiber physical properties on the resulting microcrack behavior. The lay-up for each material was [0/45/90/-45]s with a nominal ply thickness of 0.0125 cm (0.005 in). The specimens were cycled between -157°C (-250°F) and +121°C (+250°F) up to 500 times. They were examined at a magnification of x400 at different thermal cycle intervals for microcracks. It was found that although the maximum crack density varied with the ply lay-up angle, it did not vary much with fiber type. However, the fiber type had a strong influence on the rate of microcrack development. This behavior was found to be best described by fitting a hyperbolic function to the microcrack density as a function of the number of thermal cycles.
Author: K. N. Lauraitis
Publisher:
ISBN:
Category :
Languages : en
Pages : 78
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Book Description
Effect of low speed impact damage on composite materials is a new and potentially significant design condition for high performance systems. In metallic structure, damage due to tool drop, small rock impact and hail (while on the ground) did not constitute a damage of major concern. However, composites generally exhibit little inelastic ductility, are sensitive to secondary stresses, and are susceptible to splitting and delamination with cracks often propagating in the fiber direction through debonding. Upon failure, energy absorption is low. Due to these fracture characteristics and the low strain to failure, composite materials generally exhibit lower impact resistance than the metals typically used for aircraft construction. Environmental exposure may aggravate the deleterious effects of impact damage. It is well known that the mechanical properties of a polymeric matrix are susceptible to environmental degradation. Matrix cracking resulting from impact, loading or thermal cycling may provide pathways for moisture which can enter by laminar flow much more rapidly than by diffusion upon subsequent exposure to high humidity environment. Detrimental effects may also be expected because the internal tensile stress in the matrix increases with decreasing temperature, promoting crazing and the formation of microvoids.
Author: Frank W. Crossman
Publisher:
ISBN:
Category : Epoxy resins
Languages : en
Pages : 164
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Book Description
Author: DF. Adams
Publisher:
ISBN:
Category : Composite materials
Languages : en
Pages : 22
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Book Description
Results are presented of an inelastic finite-element analysis of the residual microstress state in a unidirectional graphite/epoxy composite subjected to temperature cycling from room temperature (294 K) to 405 K or a combined cycle of changing matrix moisture content from a saturated condition (5.6 percent water by weight) to 2.0 percent moisture content with a simultaneous temperature change from room temperature to 339 K. In the analysis, the graphite fibers are modeled as being transversely isotropic, and assumed temperature- and moisture-dependent properties of modulus and strength for epoxy are utilized.
Author:
Publisher: ASTM International
ISBN:
Category :
Languages : en
Pages : 299
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Author:
Publisher: ASTM International
ISBN:
Category :
Languages : en
Pages : 546
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Book Description
