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  • COMPOSITE MATERIALS  (8)
  • CHEMISTRY AND MATERIALS (GENERAL)  (3)
  • 1
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    Hygrothermal effects on the mechanical behaviour of graphite fibre-reinforced epoxy laminates beyond initial failure (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The critical load levels and associated cracking beyond which a multidirectional laminate can be considered as structurally failed has been determined by loading graphite fiber-reinforced epoxy laminates to different strain levels up to ultimate failure. Transverse matrix cracking was monitored by acoustic and optical methods. The residual stiffness and strength parallel and perpendicular to the cracks were determined and related to the environmental/loading history. Within the range of experimental conditions studied, it is concluded that the transverse cracking process does not have a crucial effect on the structural performance of multidirectional composite laminates.
    Keywords: COMPOSITE MATERIALS
    Type: Composites (ISSN 0010-4361); 17; 23-32
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  • 2
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    Residual strength of composite laminates subjected to tensile-compressive fatigue loading (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Results are presented on the measurements of the residual strengths of T300/934 graphite epoxy laminates, in tension and in compression, after the samples were exposed to tension-compression fatigue loading (R = -1). Four laminate ocnfigurations were tested: unidirectional, cross-ply, angle-ply, and quasi-isotropic. It was found that the fatigue behavior of laminates was dependent on the quasi-static strengths and the specific structure of the laminate. No direct correlation was found between remaining residual strengths and the percentage of average fatigue life. However, a correlation scheme was developed for the individual specimen under test, based on a cumulative damage model and a stiffness change of the material.
    Keywords: COMPOSITE MATERIALS
    Type: Journal of Composites Technology and Research (ISSN 0885-6804); 12; 76-84
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  • 3
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    Hygrothermal effects on mechanical behavior of graphite/epoxy laminates beyond initial failure (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An investigation was conducted to determine the critical load levels and associated cracking beyond which a multidirectional laminate can be considered as structurally failed. Graphite/epoxy laminates were loaded to different strain levels up to ultimate failure. Transverse matrix cracking was monitored by acoustic and optical methods. Residual stiffness and strength that were parallel and perpendicular to the cracks were determined and related to the environmental/loading history. Results indicate that cracking density in the transverse layers has no major effect on laminate residual properties as long as the angle ply layers retain their structural integrity. Exposure to hot water revealed that cracking had only a small effect on absorption and reduced swelling when these specimens were compared with uncracked specimens. Cracked, moist specimens showed a moderate reduction in strength when compared with their uncracked counterparts. Within the range of environmental/loading conditions of the present study, it is concluded that the transverse cracking process is not crucial in its effect on the structural performance of multidirectional composite laminates.
    Keywords: COMPOSITE MATERIALS
    Type: NASA-TM-86001 , A-9844 , NAS 1.15:86001
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  • 4
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    Physical aging in graphite/epoxy composites (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: (Previously announced in STAR as N81-21134)
    Keywords: COMPOSITE MATERIALS
    Type: Polymer Composites; 3; Jan. 198
    Format: text
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  • 5
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    Phase relations in the Fe-Ni-Cr-S system and the sulfidation of an austenitic stainless steel (1977)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The stability fields of various sulfide phases that form on Fe-Cr, Fe-Ni, Ni-Cr and Fe-Cr-Ni alloys were developed as a function of temperature and the partial pressure of sulfur. The calculated stability fields in the ternary system were displayed on plots of log P sub S sub 2 versus the conjugate extensive variable which provides a better framework for following the sulfidation of Fe-Cr-Ni alloys at high temperatures. Experimental and estimated thermodynamic data were used in developing the sulfur potential diagrams. Current models and correlations were employed to estimate the unknown thermodynamic behavior of solid solutions of sulfides and to supplement the incomplete phase diagram data of geophysical literature. These constructed stability field diagrams were in excellent agreement with the sulfide phases and compositions determined during a sulfidation experiment.
    Keywords: CHEMISTRY AND MATERIALS (GENERAL)
    Type: NASA-TM-78465 , A-7309
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  • 6
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    Stability of chromium (III) sulfate in atmospheres containing oxygen and sulfur (1978)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The stability of chromium sulfate in the temperature range from 880 K to 1040 K was determined by employing a dynamic gas-solid equilibration technique. The solid chromium sulfate was equilibrated in a gas stream of controlled SO3 potential. Thermogravimetric and differential thermal analyses were used to follow the decomposition of chromium sulfate. X-ray diffraction analysis indicated that the decomposition product was crystalline Cr2O3 and that the mutual solubility between Cr2(SO4)3 and Cr2O3 was negligible. Over the temperature range investigated, the decomposition pressure were significantly high so that chromium sulfate is not expected to form on commercial alloys containing chromium when exposed to gaseous environments containing oxygen and sulfur (such as those encountered in coal gasification).
    Keywords: CHEMISTRY AND MATERIALS (GENERAL)
    Type: NASA-TM-78504 , A-7508
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  • 7
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    Effect of moisture on the fatigue behavior of graphite/epoxy composite laminates (1979)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The form of the moisture distribution in the specimen (gradient and flat profile) was considered to establish the influence of accelerated moisture conditioning on fatigue behavior. For the gradient specimens having an average moisture content of 1.4 percent, fatigue life was reduced by a factor of 8 at all stress levels investigated. Corresponding reduction in fatigue life for the flat moisture profile specimens at the same average moisture content was comparatively smaller, being about a factor of 5 from the value in dry specimens. X-ray radiographic analysis of damage accumulation in compression-compression fatigue revealed interlaminar cracking to be the dominant mode of failure responsible for the observed enhanced cyclic degradation of moisture-conditioned specimens. This finding was corroborated by the observed systematic reduction in interlaminar shear strength as a function of moisture content, which, in turn, increased the propensity for delamination under cyclic compressive loads. Residual strength measurements on cycled specimens indicated significant strength reductions at long lives, particularly in moisture conditioned specimens.
    Keywords: COMPOSITE MATERIALS
    Type: NASA-TM-78548 , A-7689
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  • 8
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    Influence of temperature and the role of chromium on the kinetics of sulfidation of 310 stainless steel (1977)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The sulfidation of 310 stainless steel was studied over the temperature range from 910 K to 1285 K. By adjusting the ratio of hydrogen sulfide, variations in sulfur potential were obtained. The effect of temperature on sulfidation was determined at three different sulfur potentials: 39/sqNm, 0.014/sqNm, and 0.00015/sqNm. All sulfide scales contained one or two surface layers in addition to a subscale. The second outer layer (OL-II), furthest from the alloy, contained primarily Fe-Ni-S. The first outer layer (OL-I), nearest the subscale, contained FE-Cr-S. The subscale consisted of sulfide inclusions in the metal matrix. At a given temperature and sulfur potential, the weight gain data obeyed the parabolic rate law after an initial transient period. The parabolic rate constants obtained at the sulfur potential of 39/sqNm did not show a break when the logarithm of the rate constant was plotted as a function of the inverse of absolute temperature. Sulfidation carried out at sulfur potentials below 0.02/sqNm, however, did show a break at 1145 K, which is termed as the transition temperature. This break was found to be associated with the changes which had occurred in the Fe:Cr ratio of OL-I. Below the transition temperature the activation energy was found to be approximately 125 kj/mole. Above the transition temperature the rate of sulfidation decreased with temperature but dependent on the Fe:Cr ratio in the iron-chromium-sulfide layers of the OL-I. A reaction mechanism consistent with the experimental results has been proposed.
    Keywords: CHEMISTRY AND MATERIALS (GENERAL)
    Type: NASA-TM-73246 , A-7058
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  • 9
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    A temperature dependent fatigue failure criterion for graphite/epoxy laminates (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-07-27
    Description: A fatigue failure criterion applicable to composite materials is developed and applied to predict the fatigue behavior of graphite/epoxy laminates with particular emphasis on the influence of temperature. Tensile stress-strain curves and tension-tension fatigue curves for various unidirectional, angle-ply and symmetrically balanced laminates were developed at test temperatures of 25 C, 74 C and 114 C. In general for most laminates a reduction in both static strength and fatigue strength is observed with increasing temperature. This reduction appeared more severe in fatigue loading than in static tensile loading and most severe where the shear stress in the lamina is the dominant failure mode. Through an analytical formulation of shifting functions for the influences of temperature, all fatigue data are shown to be capable of being reduced to a single reference curve at some temperature. Additionally, examples are given which demonstrate the capability of the fatigue failure criterion to predict failure of complex symmetrically balanced laminates from relevant parameters obtained from the observed behavior of unidirectional and angle-ply laminates.
    Keywords: COMPOSITE MATERIALS
    Type: New developments and applications in composites; 17, 1978; Louis, MO.
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  • 10
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    Fatigue behavior of graphite-epoxy laminates at elevated temperatures (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: An examination and analysis is presented of the elevated temperature fatigue behavior of multidirectional graphite-epoxy laminates in terms of single lamina behavior. The laminate strength is predicted by considering the cyclic stress field in each lamina, the interlaminar stresses, and the experimentally determined temperature-effect 'shifting factors'. The initial failure of a lamina in a laminate is examined first in terms of stress redistribution, and then in terms of total failure and final laminate fracture; these analytical results are then compared with the actual fatigue behavior of T300/5208 graphite-epoxy composite laminates. In view of the agreement obtained, it is concluded that the temperature 'shifting factors' introduced here enable one to predict long-term behavior at a given temperature from short-time testing at elevated temperatures.
    Keywords: COMPOSITE MATERIALS
    Type: Symposium on Fatigue of fibrous composite materials; May 22, 1979 - May 23, 1979; San Francisco, CA
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