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  • 1
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    Effect of resin on impact damage tolerance of graphite/epoxy laminates (1982)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: Twenty-four different epoxy resin systems were evaluated by a variety of test techniques to identify materials that exhibited improved impact damage tolerance in graphite/epoxy composite laminates. Forty-eight-ply composite panels of five of the material systems were able to sustain 100 m/s impact by a 1.27-cm-diameter aluminum projectile while statically loaded to strains of 0.005. Of the five materials with the highest tolerance to impact, two had elastomeric additives, two had thermoplastic additives, and one had a vinyl modifier; all the five systems used bisphenol A as the base resin. An evaluation of test results shows that the laminate damage tolerance is largely determined by the resin tensile properties, and that improvements in laminate damage tolerance are not necessarily made at the expense of room-temperature mechanical properties. The results also suggest that a resin volume fraction of 40 percent or greater may be required to permit the plastic flow between fibers necessary for improved damage tolerance.
    Keywords: COMPOSITE MATERIALS
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  • 2
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    Investigating compression failure mechanisms in composite laminates with a transient fiberglass-epoxy birefringent material (1984)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: An experimental study is reported in which a nondestructive technique involving the use of a transparent fiberglass-epoxy composite birefringent material has been used to investigate compression failure mechanisms in graphite-epoxy laminates. It is shown that the birefringency and transparency of the fiberglass-epoxy material permits regions of high stress to be located and the mechanisms of local failure propagation to be identified within the laminate. The material may also be useful for studying stress fields and for identifying failure initiation and propagation mechanisms in a wide variety of composite-structure problems.
    Keywords: COMPOSITE MATERIALS
    Type: Experimental Techniques (ISSN 0732-8818); 8; 24
    Format: text
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  • 3
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    Thermogravimetric analysis of silicon carbide-silicon nitride fibers at ambient to 1000 C in air (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Thermogravimetric analysis of silicon carbide-silicon nitride fibers was carried out at ambient to 1000 C in air. The weight loss over this temperature range was negligible. In addition, the oxidative stability at high temperature for a short period of time was determined. Fibers heated at 1000 C in air for fifteen minutes showed negligible weight loss (i.e., less than 1 percent).
    Keywords: COMPOSITE MATERIALS
    Type: SAMPE Quarterly (ISSN 0036-0821); 15; 39
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  • 4
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    Effects of water during cure on the properties of a carbon/phenolic system (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The effects of prepreg water contamination on interlaminar shear strength, tranverse compressive strength, and longitudinal compressive strength were determined. Decreases in these properties due to water contamination were sugstantial: 28 percent for the interlaminar shear strength, 21 percent for the transverse compressive strength and 31 percent for the longitudinal compressive strength. Since voids were not detected by X-ray analysis, the most likely cause for these results is fiber-matrix debounding in the laminate.
    Keywords: COMPOSITE MATERIALS
    Type: SAMPE Quarterly (ISSN 0036-0821); 15; 47-49
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  • 5
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    Failure characteristics of graphite-epoxy structural components loaded in compression (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Failure characteristics of compressively loaded graphite-epoxy components are described. Experimental results for both strength-critical laminates and structural components with postbuckling strength are presented. Effects of low speed impact damage and circular holes on compressive strength are discussed. Delamination and shear crippling failure mechanisms that limit the performance of strength-critical laminates are described. Transverse shear and skin-stiffener separation failure mechanisms that limit the performance of components with postbuckling strength are also described. The influence of matrix properties on compressive strength improvements for impact damaged laminates is discussed. Experimental data and results from a failure analysis for strength-critical laminates with cutouts are discussed and compared with impact damage results. Typical postbuckling test results are compared with analytical predictions. Previously announced in STAR as N83-12174
    Keywords: COMPOSITE MATERIALS
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  • 6
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    Comparison of toughened composite laminates using NASA standard damage tolerance tests (1984)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The proposed application of composite materials to transport wing and fuselage structures prompted the search for tougher materials having improved resistance to impact damage and delamination. Several resin/graphite fiber composite materials were subjected to standard damage tolerance tests and the results were compared to ascertain which materials have superior toughness. In addition, test results from various company and NASA laboratories were compared for repeatability.
    Keywords: COMPOSITE MATERIALS
    Type: ACEE Composite Struct. Technol.; p 51-74
    Format: application/pdf
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  • 7
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    Effect of Impact Damage and Open Holes on the Compression Strength of Tough Resin/high Strain Fiber Laminates (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-16
    Description: Tests to assess the performance of composite structures damaged by impact or containing local discontinuities such as cutouts are discussed. In particular, two plate specimen test configurations which were developed to define the serverity of compression strength reduction are described; one for impact damage and the other open hole specimens. The test technique for impact specimens involves damaging the plate at selected energies, measuring the size of damage by ultrasonic C-scan techniques and measuring the residual strength in a compression load test. Open-hole specimen compression tests are conducted for several different hole diameters and the failure strain and load and mode of failure recorded. The plate specimen used in these tests is designed with length, width, thickness and laminate stiffness to ensure that overall plate buckling is not responsible for initiating failure.
    Keywords: COMPOSITE MATERIALS
    Type: Tough Composite Mater.; p 61-80
    Format: text
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  • 8
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    High Temperature Resin Matrix Composites for Aerospace Structures (1980)
    In:  CASI
    Details
    Publication Date: 2018-10-20
    Description: Accomplishments and the outlook for graphite-polyimide composite structures are briefly outlined. Laminates, skin-stiffened and honeycomb sandwich panels, chopped fiber moldings, and structural components were fabricated with Celion/LARC-160 and Celion/PMR-15 composite materials. Interlaminar shear and flexure strength data obtained on as-fabricated specimens and specimens that were exposed for 125 hours at 589 K indicate that epoxy sized and polyimide sized Celion graphite fibers exhibit essentially the same behavior in a PMR-15 matrix composite. Analyses and tests of graphite-polyimide compression and shear panels indicate that utilization in moderately loaded applications offers the potential for achieving a 30 to 50 percent reduction in structural mass compared to conventional aluminum panels. Data on effects of moisture, temperature, thermal cycling, and shuttle fluids on mechanical properties indicate that both LARC-160 and PMR-15 are suitable matrix materials for a graphite-polyimide aft body flap. No technical road blocks to building a graphite-polyimide composite aft body flap are identified.
    Keywords: COMPOSITE MATERIALS
    Type: Selected NASA Research in Composite Materials and Structures; 143-182
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  • 9
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    Shear-lag analysis of notched laminates with interlaminar debonding (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The fracture behavior of a debonded zone of finite width with no longitudinal damage in the unidirectional ply is predicted and the solution is then extended to include longitudinal matrix yielding and splitting in the unidirectional ply at the crack tip. The shear-lag assumption is used to describe the shear transfer between fibers. The fracture behavior of the laminate is studied as a function of initial crack length, constraint ratio, and width of the debonded zone. Results indicate that debonding can reduce the maximum fiber stress at the crack tip on the order of ten percent. This effect is maximum for a debond width of two or three fiber spacings and is independent of the initial crack length. As the debond width grows beyond this point, the maximum stress increases. For widths of about ten fiber spacings or more, the maximum fiber stress is larger than for the fully bonded case. In the presence of longitudinal matrix damage the same general behavior is found; however, the location of the maximum fiber stress is quite complex.
    Keywords: COMPOSITE MATERIALS
    Type: NASA-CR-3798 , NAS 1.26:3798
    Format: application/pdf
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  • 10
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    Mathematical modeling of damage in unidirectional composites (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Extending the work of Goree and Gross (1979), solutions are given for a two-dimensional region of unidirectional fibers embedded in an elastic matrix whose initial flaw may take the form of a transverse notch, a rectangular cutout, or a circular hole. Subsequent flaw-induced damage is generated by remote stresses acting parallel to the fibers. For the case of such ductile matrix composites as boron/aluminum, present results indicate that both longitudinal matrix yielding and transverse notch extension must be included in order for the model to agree with experimental results. Little difference is found for the three types of initial damage considered. In all cases, the presence of additional damage changes the nature of stress distribution through the unbroken fibers.
    Keywords: COMPOSITE MATERIALS
    Type: Engineering Fracture Mechanics (ISSN 0013-7944); 17; 6 19; 1983
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