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  • 1
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    Unknown
    Electroosmotic Reduction of Ocean Bottom Breakout Forces and Times (1975)
    Canadian Science Publishing
    Details
    Publication Date: 1975-08-01
    Description: Laboratory model pullout tests were conducted with a cylindrical object, 1 sediment, 1 object in situ time, 3 electrode configurations, and electric potential gradients of 0, 0.25, and 0.5 V/cm to determine the effect of electroosmosis on reducing force and time requirements for breaking objects free of soft sediments.Results show electroosmosis to be very effective in reducing breakout times. The relationship between the breakout force ratio and breakout time can be expressed in terms of 2 empirical parameters. Electrical power requirements to achieve breakout appear to be independent of electrode configurations but do depend on electric potential gradients.
    Print ISSN: 0008-3674
    Electronic ISSN: 1208-6010
    Topics: Geosciences
    Published by Canadian Science Publishing
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    PAPER CURRENT
  • 2
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    Development of a laminate fatigue analysis (1980)
    In:  CASI
    Details
    Publication Date: 2006-06-26
    Description: A fatigue analysis technique developed to predict damage growth in notched laminates is described. Features of the analysis include: criteria to relate matrix failure to cyclic stresses in and between plies; correlation of delamination growth with strain-release rate; and in-plane shear modulus change is related to cyclic shear stresses. A simplified finite element model is used to determine stresses in laminates that contain matrix damage. Failure criteria are integrated with the finite element model to form the fatigue analysis.
    Keywords: COMPOSITE MATERIALS
    Type: Selected NASA Res. in Composite Mater. and Struct.; p 79-106
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    X-ray method shows fibers fail during fatigue of boron-epoxy laminates (1975)
    In:  Other Sources
    Details
    Publication Date: 2011-08-16
    Description: A method proposed for studying progressive fiber fracture in boron-epoxy laminates during fatigue tests is described. It is based on the intensity of X-ray absorption of the tungsten core in the boron filaments as contrasted with that of the boron and epoxy matrix. When the laminate is X-rayed, the image of the tungsten in the born filaments is recorded on a photographic plate. Breaks in the boron laminates can be easily identified by magnifying the photographic plates. The method is suitable for studying broken boron filaments in most matrix materials, and may supply key information for developing realistic fatigue and fracture models.
    Keywords: COMPOSITE MATERIALS
    Type: Journal of Composite Materials; 9; Oct. 197
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    Cyclic debonding of unidirectional composite bonded to aluminum sheet for constant-amplitude loading (1976)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Cyclic debonding rates were measured during constant-amplitude loading of specimens made of graphite/epoxy bonded to aluminum and S-glass/epoxy bonded to aluminum. Both room-temperature and elevated-temperature curing adhesives were used. Debonding was monitored with a photoelastic coating technique. The debonding rates were compared with three expressions for strain-energy release rate calculated in terms of the maximum stress, stress range, or a combination of the two. The debonding rates were influenced by both adherent thickness and the cyclic stress ratio. For a given value of maximum stress, lower stress ratios and thicker specimens produced faster debonding. Microscopic examination of the debonded surfaces showed different failure mechanisms both for identical adherends bonded with different adhesive and, indeed, even for different adherends bonded with identical adhesives. The expressions for strain-energy release rate correlated the data for different specimen thicknesses and stress ratios quite well for each material system, but the form of the best correlating expression varied among material systems. Empirical correlating expressions applicable to one material system may not be appropriate for another system.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TN-D-8126 , L-10480
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 5
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    Fatigue damage of notched boron/epoxy laminates under constant-amplitude loading (1977)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Fatigue damage in (0, plus or minus 45) and (0, plus or minus 45, 90) boron/epoxy laminates was studied with X-ray radiography and scanning electron microscopy. In addition, limited tests for residual strength and stiffness were performed. Initially, fatigue damage in both (0, plus or minus 45) and (0, plus or minus 45, 90) laminates occurred as intralaminar cracks around the edge of the hole. Then, whenever further damage developed, intralaminar cracks in the plus or minus 45-deg plies began to propagate from the edge of the hole. Finally, in both types of laminates, primarily plus or minus 45-deg fibers broke (prior to two-piece failure) where intralaminar cracks in the plus or minus 45-deg plies had occurred. In the (0, plus or minus 45) laminates, the 45-deg plies developed intralaminar and transthickness cracks along lines parallel to the loading axis and tangent to the hole in the test specimen. This damage, which was most pronounced under compressive loads, had little effect on either strength or stiffness. In contrast, in the (0, plus or minus 45, 90) laminates, the plus or minus 45-deg plies developed intralaminar cracks transverse to the loading axis.
    Keywords: COMPOSITE MATERIALS
    Type: Symposium on Fatigue of filamentary composite materials; Nov 15, 1976 - Nov 16, 1976; Denver, CO
    Format: text
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    NASA TECHNICAL REPORTS
  • 6
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    Fatigue damage of notched boron/epoxy laminates under constant amplitude loading (1976)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Fatigue damage in (0, + or - 45) and (0, + or - 45,90) boron/epoxy laminates was studied with X-ray radiography and scanning electron microscopy. In addition, limited tests for residual strength and stiffness were performed. The results of this study suggest that in boron/epoxy laminates the 45-degree plies play a key role in the fatigue process of boron/epoxy laminates that contain them. The fatigue process in the + or - 45-degree plies starts as intralaminar matrix cracks.
    Keywords: COMPOSITE MATERIALS
    Type: NASA-TM-X-73994 , ASTM Symp. on Fatigue of Filamentary Composites; Nov 15, 1976 - Nov 18, 1976; Denver
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 7
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    Debond propagation in composite-reinforced metals (1975)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Strain energy release rates were used to correlate cyclic debonding between metal sheets and composite reinforcement. An expression for the strain energy release rate was derived and applied to fatigue test results for three material systems: graphite bonded to aluminum with both a room temperature and an elevated temperature curing adhesive; and, S-glass bonded to aluminum with an elevated temperature curing adhesive. For each material system, specimens of several thicknesses were tested with a range of fatigue loads. Cyclic debonding was monitored using a photoelastic technique. A close correlation was found between the observed debond rates and the calculated strain energy release rates for each material system.
    Keywords: COMPOSITE MATERIALS
    Type: Fatigue of composite materials; Symposium; Dec 03, 1973 - Dec 04, 1973; Bal Harbour, FL
    Format: text
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    NASA TECHNICAL REPORTS
  • 8
    facet.materialart.
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    Debond propagation in composite reinforced metals (1974)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Strain energy release rates were used to correlate cyclic debonding between metal sheets and composite reinforcement. An expression for the strain energy release rate was derived and applied to fatigue test results for three material systems: graphite bonded to aluminum with both a room temperature and an elevated temperature curing adhesive, and S-glass bonded to aluminum with an elevated temperature curing adhesive. For each material system, several thicknesses were tested with a range of fatigue loads. Cyclic debonding was monitored using a photoelastic technique. A close correlation was found between the observed debond rates and the calculated strain energy release rates for each material system.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-X-71948 , ASTM Symp. on Fatigue of Composite Mater.; Dec 02, 1973 - Dec 07, 1973; Bal Harbour, FL; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 9
    facet.materialart.
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    Crack propagation in aluminum sheets reinforced with boron-epoxy (1979)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: An analysis was developed to predict both the crack growth and debond growth in a reinforced system. The analysis was based on the use of complex variable Green's functions for cracked, isotropic sheets and uncracked, orthotropic sheets to calculate inplane and interlaminar stresses, stress intensities, and strain-energy-release rates. An iterative solution was developed that used the stress intensities and strain-energy-release rates to predict crack and debond growths, respectively, on a cycle-by-cycle basis. A parametric study was made of the effects of boron-epoxy composite reinforcement on crack propagation in aluminum sheets. Results show that the size of the debond area has a significant effect on the crack propagation in the aluminum. For small debond areas, the crack propagation rate is reduced significantly, but these small debonds have a strong tendency to enlarge. Debond growth is most likely to occur in reinforced systems that have a cracked metal sheet reinforced with a relatively thin composite sheet.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-80056
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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