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  • 1
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    Buckling and postbuckling research on flat and curved composite panels (1980)
    In:  CASI
    Details
    Publikationsdatum: 2006-06-26
    Beschreibung: Progress in the development of verified design technology for generic advanced-composite structural components loaded in compression is reported. Generic structural configurations material systems and load ranges of interest for a given application were investigated using structural procedures, structural analysis procedures, and laboratory testing of structural specimens. Both flat and curved composite compression panels that are designed either to be buckling resistant or to have postbuckling strength depending on the expected application of the panels were considered.
    Schlagwort(e): COMPOSITE MATERIALS
    Materialart: Selected NASA Res. in Composite Mater. and Struct.; p 35-78
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  • 2
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    Evaluation of long-duration exposure to the natural space environment on graphite-polyimide and graphite-epoxy mechanical properties (A0175) (1984)
    In:  CASI
    Details
    Publikationsdatum: 2006-02-14
    Beschreibung: The primary objective of this experiment is to accumulate the needed operational data associated with the exposure of graphite-polyimide and graphite-epoxy material to the environments of space. The experiment will be mounted in two 3-in.-deep peripheral trays. Graphite-polyimide specimens will occupy 1 1/3 trays and the graphite-epoxy specimens will occupy two-thirds of a tray. The experiment approach requires two matched sets of specimens with traceable records that are maintained for materials processing and specimen quality. After fabrication, one set of each test specimen will be sectioned and structurally tested to serve as a data baseline. After the flight, the other set of specimens will undergo extensive measurements of mechanical properties for comparison with the original data baseline. Structural testing of the graphite-polyimide specimens will provide strength and elastic data in tension, compression, and shear. Transverse tension microcracking and crack propagation will be evaluated by photomicroscopy. Structural testing of the graphite-epoxy specimens will include verification of laminate, core, adhesive, and fatigue properties as applied to the design and analysis of the payload bay door. Microcracking and crack propagation will also be analyzed by photomicroscopy.
    Schlagwort(e): COMPOSITE MATERIALS
    Materialart: NASA. Langley Research Center Long Duration Exposure Facility (LDEF); p 38-40
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  • 3
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    Durability/life of fiber composites in hygrothermomechanical environments (1982)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-18
    Beschreibung: Statistical analysis and multiple regression were used to determine and quantify the significant hygrothermomechanical variables which influence the tensile durability/life (cycle loading, fatigue) of boron-fiber/epoxy-matrix (B/E) and high-modulus-fiber/epoxy-matrix (HMS/E) composites. The use of the multiple regression analysis reduced the variables from fifteen, assumed initially, to six or less with a probability of greater than 0.999. The reduced variables were used to derive predictive models for compression and intralaminar shear durability/life of B/E and HMS/E composites assuming isoparametric fatigue behavior. The predictive models were subsequently generalized to predict the durability/life of graphite/fiber-r generalized model is of simple form, predicts conservative values compared with measured data and should be adequate for use in preliminary designs. Previously announced in STAR as N82-14287
    Schlagwort(e): COMPOSITE MATERIALS
    Format: text
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  • 4
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    Prediction of composite hygral behavior made simple (1982)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: A convenient procedure is described to determine the hygral behavior (moisture expansion coefficients and moisture stresses) of angleplied fiber composites using a pocket calculator. The procedure consists of equations and appropriate graphs for various (+ or - theta) ply combinations. These graphs present reduced stiffness and moisture expansion coefficients as functions of (+ or - theta) in order to simplify and expedite the use of the equations. The procedure is applicable to all types of balanced, symmetric fiber composites including interply and intraply hybrids. The versatility and generality of the procedure is illustrated using several step-by-step numerical examples. Previously announced in STAR as N82-16181
    Schlagwort(e): COMPOSITE MATERIALS
    Materialart: SAMPE Quarterly (ISSN 0036-0821); 14; 30-39
    Format: text
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  • 5
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    Ultrasonic and mechanical characterizations of fatigue states of graphite epoxy composite laminates (1982)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-18
    Beschreibung: Results of an exploration of the relationship between ultrasonic attenuation and fatigue survivability of graphite fiber epoxy composites fabricated under different cure conditions are reported. A total of 9 27 x 40 cm eight-ply graphite epoxy laminated specimens were formed, and fatigue tests were run on five partial samples at 73.5 N varying at 30 Hz, with tests ending at a 1.27 cm deflection. A pulsed oscillator generated sinusoidal waves and transducers recorded the passage of the ultrasonic waves for display on oscilloscopes. Cure pressures ranged from 0.52-0.85 MPa and cure temperatures were in the 150-200 C interval. Ultrasonic through-transmission at 4 MHz was performed prior to and during fatigue testing. The minimum void volume fraction occurred at 175 C and 0.86 MPa. The flexural stiffness decreased with the number of fatigue cycles past 10,000, when the attenuation also increased. Correlations were found between the 4.0 MHz signal attenuation and the void volume fraction, and between the number of fatigue cycles to failure and the 4.0 MHz signal attenuation.
    Schlagwort(e): COMPOSITE MATERIALS
    Materialart: Materials Evaluation; 40; Apr. 198
    Format: text
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  • 6
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    Dynamic crack propagation and arrest in orthotropic DCB fiber composite specimens (1981)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-18
    Beschreibung: An orthotropic double cantilever beam (DCB) model is used to study dynamic crack propagation and arrest in 90 deg unidirectional Hercules AS/3501-6 graphite fiber epoxy composites. The dynamic fracture toughness of the composite is determined from tests performed on the long-strip specimen and DCB crack arrest experiments are conducted. By using the dynamic fracture toughness in a finite-difference solution of the DCB governing partial differential equations, a numerical solution of the crack propagation and arrest events is computed. Excellent agreement between the experimental and numerical crack arrest results are obtained.
    Schlagwort(e): COMPOSITE MATERIALS
    Materialart: Engineering Fracture Mechanics; 14; 2, 19; 1981
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  • 7
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    Ultrasonic attenuation and velocity in AS/3501-6 graphite fiber composite (1980)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-18
    Beschreibung: The ultrasonic group velocity and attenuation were measured as a function of frequency for longitudinal and shear waves in the Hercules epoxy matrix (3501-6) and in the principal directions of the unidirectional Hercules graphite fiber epoxy composite (AS/3501-6). Tests were conducted in the frequency ranges 0.25-14 MHz and 0.5-3 MHz for longitudinal and shear wave modes, respectively. While the attenuation increased with frequency for all wave modes, the group velocity was independent of frequency for all wave modes. In studying the effects of transducer-specimen interface couplant and pressure, it was found that for each transducer, there exists a frequency-dependent 'saturation pressure' corresponding to the maximum output amplitude of the signal.
    Schlagwort(e): COMPOSITE MATERIALS
    Materialart: Journal of Nondestructive Evaluation; 1; June 198
    Format: text
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  • 8
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    An equation for bolt clampup relaxation in transient environments (1982)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-18
    Beschreibung: (Previously announced in STAR as N82-25327)
    Schlagwort(e): COMPOSITE MATERIALS
    Materialart: Composites Technology Review; 4; Winter 1
    Format: text
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  • 9
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    DC calibration of the strain sensitivity of a single mode optical fiber interferometer (1981)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-18
    Beschreibung: The strain sensitivity of an optical fiber interferometer developed for the detection of pulsed ultrasonic waves in solids was calibrated. Light from the output ends of both fibers was superimposed to form an interference fringe pattern that was interrogated in the far field to give a signal proportional to the differential optical fiber path length. Strain sensitivity is determined by comparing data obtained by clamping and bending the bar at different lengths to simple cantilever beam theory. A minimum theoretical detectable strain of less than 10 to the minus 10th power is indicated.
    Schlagwort(e): COMPOSITE MATERIALS
    Materialart: Va. Polytech. Inst. and State Univ. Opt. Fiber Interferometer for the Study of Ultrasonic Waves in Composite Mater.; p 13-15
    Format: text
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  • 10
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    Detection of ultrasonic waves in solids by an optical fiber interferometer (1981)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-18
    Beschreibung: An optical fiber interferometer was developed for the detection of ultrasonic waves in solids. The optical paths in both the signal and reference arms of the Mach-Zehnder interferometer are through the cores of similar lengths of single mode fiber mode stripped at both input and output. Instantaneous translation of the pattern is proportional to the localized strain produced by ultrasonic bulk waves generated in the disc and integrated along the fiber path. By spatially filtering the moving fringe pattern and synchronously demodulating the filtered optical intensity distirbution, a signal proportional to the integrated strain is obtained.
    Schlagwort(e): COMPOSITE MATERIALS
    Materialart: Va. Polytech. Inst. and State Univ. Opt. Fiber Interferometer for the Study of Ultrasonic Waves in Composite Mater.; p 7-11
    Format: text
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