« PreviousContinue »
Degradation date of Kevlar pressure vessels, W. D. Humphrey, SP563, pp. 177-197 (Oct. 1979).
Key words: degradation; epoxy resins; Kevlar 49; moisture; onc-tenth scale motor case; S-glass; temperature effects; water boil.
Recent hydroburst tests of Kevlar/epoxy composite pressure vessels showed losses in strength when subjected to extended periods of high temperature and high humidity. These pressure vessels had served to monitor the aging characteristics of Rocket Motor Cases during Engineering Development tests. Since Kevlar was a relatively new material replacing fiberglass in this application, it was considered important that these results be verified in a controlled experiment utilizing accelerated aging methods.
To measure these effects, two series of tenth-scale models of Rocket Motor Cases were fabricated, which included two different resin systems and two very different design concepts. The accelerated degradation of Kevlar composites from high temperature and humidity was evaluated by means of water boil tests for periods of up to ten days.
Hydroburst tests of these aged vessels showed Kevlar to have much less degradation than fiberglass. Actual values were determined to be dependent on the resin system used and also dependent upon the dryness of the composite at the time of test. Wet composites acted as if a plasticizer was added to the resin system and in the configuration tested actually regains virgin strength.
It is developed, by engineering analysis, that composites of glass fibers, graphite fibers, or their combination, bonded into a resinous matrix of thermo-setting polyester or epoxy are uniquely suited to these purposes. These composites have extremely high strength-to-weight ratio, excellent durability and excellent fatigue characteristics, all unaltered through wide environmental extremes. Additional advantages are that the flexural characteristics of the material can be designed, through stress-directed fibers, to suit the purpose; and that glass fibers are nonyielding, i.e., yield and ultimate strength are the same, meaning that lower safety factors can be used. Such composites are ideally suited for handling, for the storage and release of energy and for the durability required of rough treatment.
An important and large scale application is limbs for bows used in archery. Design parameters would be light weight, high strength, fatigue resistance and quick energy release.
The limbs may be solid FRP composites, or FRP composites in the form of "backing" which is laminated to wood cores. In either case the limb is formed to a taper in order to minimize weight and to reduce inertia and present a low profile to wind resistance upon release. Load requirements are almost purely flexural, therefore fiber orientation is 100% parallel to the longitudinal axis of the limb. Glass or graphite fiber content is usually in the order of 70%. The limb has a flexural strength of approximately 150,000 psi, and a flexural modulus of 5.5 x 10* psi. High heat-distortion resins are used so that the bow can be stored in automobile trunks where temperatures can go above 150 °F. An aesthetically attractive, abrasive-resistant finish is usually applied to the limb.
Additional applications in archery are bows molded entirely in one piece, and arrow shafts.
Design assurance of a leak fallure mode for composite overwrapped metal tankage, W. W. Schmidt, SPS63, pp. 198-207 (Oct. 1979).
Key words: composite materials; critical flaw size; cyclic fatigue life; filament wound tankage; leakage failure mode; linear elastic fracture mechanics; metal liner.
Assuring a leakage failure mode requires that the outer composite shell be designed such that its minimum cyclic fatigue life is approximately an order of magnitude greater than that of the metal liner. This requires making an accurate fatigue life prediction for both the composite shell and metal liner. It is further possible to determine the critical flaw size for unstable crack growth within the metal liner by application of fracture mechanics principles. A semiempirical formula has been developed for this purpose since the stresses induced in the metal liner upon initial pressurization exceed the yield strength of the liner material in all cases, which violates a basic assumption of linear elastic fracture mechanics. It is often found that the critical flaw depth is greater than the thickness dimension of the metal liner. In these instances, leakage will occur prior to unstable crack growth. For designs in which unstable crack growth can occur, a dynamic analysis has been developed. This analysis provides a means of assessing the magnitude of shock induced stresses in the composite shell due to the sudden loss of the liner's load carrying capability. Details of these design procedures are provided.
Holographic nondestructive evaluation of spherical kevlar/epoxy pressure vessels, D. M. Boyd and B. W. Maxfield, SP563, pp. 211-212 (Oct. 1979).
Key words: composites; holography; interferometers; matrix crazing; nondestructive testing; pressure vessels.
Three spherical kevlar/epoxy pressure vessels were evaluated using holographic interferometry. The holographic interferograms provide information on the failure modes, displacement profile, and possible fiber damage. The holograms show a symmetric anisotropic displacement pattern even though the vessels failed due to a leak in the aluminum mandrels. The presence of a biconvex fringe pattern found during the testing of vessel three is believed to indicate matrix crazing. This information would be useful for burst-type failure analysis. Holographic interferometry has been shown to supply information on the characteristics of kevlar/epoxy pressure vessels under stress.
The Air Force “Manufacturing Cost/Design Guide (MC/DG)", B. R. Noton and D. L. Shunk, SP563,
226227 (Oct. 1979).
Key words: airframe structure; cost-trade comparisons; manufacturing technologies; structural performance/cost trade-offs.
Composite materials in recreational equipment, D. Ratchford, SPS63, p. 208 (Oct. 1979).
Key words: composites; durability; (lexural characteristics; recreational equipment; strength-to-weight ratio.
The general requirements of materials for recreational equipment are discussed, these being high strength-toweight ratio, fatigue resistance, the ability to store and release energy, durability, aesthetic acceptability, and manufacturing capability.
The purpose of the MC/DG is to enable designers at all levels to conduct, firstly, urgently needed, quick, simple, cost-trade comparisons of manufacturing processes, and, secondly, structural performance/cost trade-offs on both components and subassemblies. The MC/DG will consist of two volumes—“Airframe Structure” and “Manufacturing Technologies." The MC/DG is being developed for the Air Force by a team consisting of Battelle's Columbus Labora
tories (BCL) and the following aerospace co
companies: General Dynamics Corporation, Fort Worth Division; Grumman Aerospace Corporation; Lockheed-California Company; Northrop Corporation, Aircraft Group; Rockwell International Corporation, Los Angeles Division.
Tensile strength and failure modes of boron-epoxy composite with a notch, C. E. S. Veng, SP563, pp. 228-238 (Oct. 1979).
Key words: boron-epoxy; edge cracks; failure modes; finite element method; tensile strength.
The purpose of this paper is to study the tensile strength and failure modes of boron-epoxy composites with an edged notch. Through the use of finite element crack program, both heterogeneity and orthotropy of material properties are brought into consideration in this paper. For comparison purposes, tension tests of actual composite samples with notches are also performed. Notch insensitivity and the failure modes are discussed. The fracture toughness of the test material is also determined. The results obtained here are important for further understanding of the failure of unidirectional boron-epoxy advanced composites.
Failure criteria for composites under complex loading, P. W. Mast, L. A. Beaubien, D. R. Mulville, S. A. Sutton, R. W. Thomas, J. Tirosh, and I. Wolock, SP563, p. 241 (Oct. 1979).
One of the common failure modes in fibrous composite laminates involves interlaminar cracks which delamination. Several questions arise in the course of a delamination analysis. Notably these include (a) how is a delamination initiated? (b) under what condition will a delamination grow? and (c) what determines the stability of a delamination growth? Owing to the unusual complexity of composite laminate systems, there appears no simple way to answer these questions satisfactorily.
In this paper, a method is developed based on the energy principle of the classical linear fracture mechanics, in order to describe the various aspects of the delamination mechanisms. Specifically, free-edge induced delamination failure in some epoxy based composite laminates are investigated employing this method. And, the results obtained are compared with experiments. It will be shown that the energy method predicts well frec-edge delamination in laminates under uniaxial tension, including the initiation, the growth and the growth stability of the delamination.
Current developments in advanced composites for naval ship application, J. J. Kelly and H. H. Vanderveldt, SP563, pp. 267-275 (Oct. 1979).
Key words: composites; hydrofoils; maintenance requirements; naval ship application.
The reasons for and the limitations on the use of composites for ship applications are described. The current exploratory development program in advanced composites for Navy ship applications emphasizes high performance craft such as hydrofoils. The future program will complete these efforts and stress broader applications for composites. Development of fire resistant composites, survivable structural concepts and materials which reduce maintenance requirements will be emphasized.
Key words: bonded joints; composites; failure criteria; inplane loads.
Studies are in progress to develop failure criteria for composites and bonded joints under a broad range of inplane loads. Criteria for predicting the conditions under which a defect will grow in composites structural components, in such applications as Naval high performance craft, will be demonstrated. Validity of a new technique for determining failure criteria for composites has been verified in laboratory tests.
Failure analysis of an idealized composite damage zone, C. T. Herakovich and D. A. O'Brien, SP563, pp. 242-254 (Oct. 1979).
Key words: compression; failure; finite elements; graphiteepoxy; interlaminar stresses; laminated composites; stress concentrations; tension; tensor polynomial.
First failure of finite width laminates with an idealized composite damage zone is analyzed through the use of a linear elastic finite element stress analysis and the tensor polynomial failure criterion. Crossply and angleply (145). laminates are analyzed under tension and compression loading. It is shown that a boundary layer exists near the damage zone which is very similar to the boundary layer which has been shown previously to exist along free edges. Comparisons are made between predicted initial failure of damaged and undamaged laminates. Transverse tension is the dominate mode of failure fo: tensile loading, but compressive loading leads to a variety of failure modes depending upon the laminate configuration.
Environmental effects on fiber reinforced organic matrix composites, M. Silvergleit, A. B. Macander, F. A. Brauer, and H. P. Edelstein, SP563, pp. 276-285 (Oct. 1979).
Key words: advanced composites; cavitation erosion; extended immersion; flammability; glass reinforced plastics; graphite epoxy; impact; marine environment.
A review is presented on the effects of the marine environment on fiber reinforced organic matrix composites. In addition to the effects of extended immersion in seawater on composite properties, the limiting utility of composites due to cavitation erosion, flammability and smoke spread evolution and damage due to impact are discussed. In general, high quality, low void content glass reinforced plastics (GRP) and graphite epoxy composites retain over 90% of their initial strength after three years immersion in seawater. Organic matrix composites, which are subjected to high speed fluid flow are degraded by erosion due to the collapse of the cavitation cloud, however, erosion resistance 'can be improved by using elastomeric or thin metallic overlays. With the exception of polyimides, organic matrix composites have poor resistance to flammability and emit large quantities of dense smoke. Impact resistance of composites is a function of fiber/resin properties and composite orientation. Incorporation of high toughness flexible matrices and/or high strength, low modulus fibers will increase composite impact resistance.
Interlaminar failure epoxy based composite laminates, A. S. Wang, F. W. Crossman, and G. E. Law, Jr., SP563, pp. 255-264 (Oct. 1979).
Key words: delamination mechanisms; energy release rate; finite element method; free-edge stresses; graphite epoxy composites; interlaminar cracks; stability of cracks; virtual crack closure.
Composite technology for marine application, W. P. Couch, SP563, pp. 286-298 (Oct. 1979).
Key words: advanced composites; advanced ships; elastic properties; fatigue tests; nondestructive tests; structural analysis; ultimate strength.
Under the sponsorship of the Naval Sea Systems Command (NAVSEA 035), the David W. Taylor Naval Ship Research and Development Center (DTNSRDC) has been conducting a program to assess the current technology status of advanced composites, and to determine the feasibility of application to marine structures. The approach being utilized to achieve this objective involves a coordinated structures/materials community effort seeking input from private industry and other government agencies. As a result of feasibility studies performed by the McDonnell Douglas Astronautics Company and the Grumman Aerospace Corporation and a review of high payoff areas for structural application of advanced composites by the Naval Ship Composites Community, the hydro-foil strut/foil system was selected as the primary structural element to evaluate the use of advanced composites for advanced naval ship structures. Two subcomponents were selected for this evaluation; a foil test component (tapered box beam), and a hydrofoil control flap. Concurrently, analytical methods incorporating composite mechanics developed by the aerospace composites program are reviewed, modified and utilized when applicable to determine the structural behavior for marine, load-carrying components. In addition, preliminary design studies are conducted on other naval ship structures to determine the feasibility of composite construction. The following text describes the current effort under investigation related to the four program subtasks: box beam validation, foil flap validation, analytical methods and design application studies.
SP565. A history of walkway slip-resistance research at the Na
tional Bureau of Standards, S. C. Adler and B. C. Pierman, Nat. Bur. Stand. (U.S.), Spec. Publ. 565, 36 pages (Dec. 1979) SN003-003-02142-3.
Key words: friction; measurement; reference standards;
safety research; walkway slip-resistance. This report summarizes NBS research in the area of walkway and shoe slip-resistance measurement since 1924 and outlines current activities that will provide a technical basis for slip-resistance measurement. The work of Sigler, Hunter, Boone and Brungraber represents the historic perspective. Current activities in data base development and identification of standard reference surfaces contribute to a rational basis for quantitative slip-resistance criteria for building codes and standards. Proposed future research thrusts include personal factors such as human biokinetic and perceptual variables, as well as environmental factors such as lighting in the built environment. This research will contribute to the development of new intervention strategies to reduce deaths and injuries due to slips and falls.
5.8. NATIONAL STANDARD REFERENCE DATA SERIES
NSRDS-NBS3, Section 8. Selected tables of atomic spectra. A:
Atomic energy levels–Second edition. B: Multiplet tables. O VI, O VII, O vill, C. E. Moore, Nat. Stand. Ref. Data Ser., Nai. Bur. Stand. (U.S.), 3, Sec. 8, 31 pages (Jan. 1979) SN003-003-01964-0.
Key words: atomic energy levels, O v1-O vili; atomic spectra, O vi-O vir; multiplet tables, O vi-O vill; oxygen, spectra, O vi-O vil; spectra, O vi-O vir; wavelengths, O vi-O
A review of the properties of the two dimensional superionic conductors of the sodium beta alumina family is presented, with emphasis on the variability of properties with composition and processing. Processing methods, including methods of distributing additives, may strongly influence engineering properties of these substances through changes in microstructures. Described are common methods of measurement of properties with generally accepted ranges of property values. The need to compromise in the design of devices requiring several coincident optimal properties is, at this time, a necessary ingredient in the use of these materials as device components. NSRDS-NBS64. Rate coefficients for ion-molecule reactions. Or
ganic ions other than those containing only C and H, L. W. Sieck, Nat. Stand. Ref. Data Ser., Nat. Bur. Stand. (U.S.), 64, 27 pages (Feb. 1979) SN003-003-02027-3.
Key words: chemical kinetics; data evaluation; gas phase ion-molecule reactions;
spectrometry; organic molecules; rate coefficients. A compilation is presented of all experimentally determined bimolecular and termolecular rate coefficients for the reactions of organic ions (other than those containing only C and H) with neutral molecules in the vapor phase. The literature covered is from 1960 to the present, and both positive and negative ions are considered. Five hundred and seventy-seven separate reaction-partners are tabulated, and experimental conditions are specified wherever possible. Preferred values are suggested for a number of these processes.
The present publication is the eighth Section of a series being prepared in response to the need for a current revision of two sets of the author's tables containing data on atomic spectra as derived from analyses of optical spectra. As in the previous Sections, Part A contains the atomic energy levels and Part B the multiplet tables. Section 8 includes these data for O vi, O VII, and O vill, thereby completing the spectra of oxygen. The form of presentation is described in detail in the text to Section 1.
NSRDS-NBS61, Part II. Physical properties data compilations
relevant to energy storage. II. Molten salts: Data on single and multi-component salt systems, G. J. Janz, C. B. Allen, N. P. Bansal, R. M. Murphy, and R. P. T. Tomkins, Nat. Stand. Ref. Data Ser., Nat. Bur. Stand. (U.S.), 61, Part II, 442 pages (Apr. 1979) SN003-003-02051-6.
Key words: corrosion; data compilation; electrochemical energy storage materials; molten salts; physical properties; safety and hazards; thermal energy storage materials; thermal properties; thermodynamic properties; transport pro
perties. The present work provides selected data with value judgements for a set of 49 salt systems of interest as candidate materials for thermal energy storage sub-systems and for electrochemical energy storage systems. The physical properties assessed are: melting points; phase diagrams; eutectic compositions; density; surface tension; viscosity; electrical conductivity; diffusion constants for ions; heat of fusion; heat capacity; volume change on fusion; vapor pressure; thermal conductivity (liquid and solid); and cryoscopic constant. The status of corrosion studies in the form of annotated bibliographic summaries, and salient observations on safety and hazards are also reported. A summarizing series of tables is provided as index to the data-gaps status for this set of candidate materials.
NSRDS-NBS65. Rate constants for reactions of inorganic radi
cals in aqueous solution, A. B. Ross and P. Neta, Nat. Stand. Ref. Data. Ser., Nat. Bur. Stand. (U.S.), 65, 62 pages (June 1979) SN003-003-02072-9.
Key words: aqueous solution; carbonate radical; chemical kinetics; halogen radical anions; nitrate radical; oxyanion radicals; phosphate radical; photolysis; radiolysis; rates; selenium radicals; sulfate radical; thiocyanate radical
anion. Rate constants have been compiled for reactions of various transient inorganic radicals produced by radiolysis or photolysis in aqueous solution. Data are included for the carbonate radical, sulfate radical, phosphate radical, nitrate radical and other nitrogen-, sulfur- and selenium-containing radicals, and the halide and pseudohalide radicals Cla", Brą , la , and (SCN),: The radicals react with other inorganic ions, as well as aliphatic, aromatic and heterocyclic compounds.
NSRDS-NBS61, Part III. Physical properties data compilations
relevant to energy storage. III. Engineering properties of single and polycrystalline sodium beta and beta"-alumina, G. R Miller and D. G. Paquette, Nat. Bur. Stand. Ref. Data Ser., Nar. Bur. Stand. (U.S.), 61, Part III, 19 pages (June 1979) SN003-003-02079-6.
Key words: battery application; engineering properties data; evaluated data; polycrystalline; single crystal, sodium beta alumina; sodium beta double prime alumina.
5.9. BUILDING SCIENCE SERIES
Disseminates technical information developed at the Bureau on building materials, components, systems, and whole structures. The series presents research results, test methods, and performance criteria related to the structural and environmental functions and the durability and safety characteristics of building elements and systems.
Key words: anchors; mobile home foundations; soil
anchors; soil mechanics; wind upset. Available anchor hardware is surveyed and evaluated and pull-out capacity data are compared with hypotheses for predicting anchor pull-out capacity based on soil mechanics principles. The evidence suggests that our ability to predict anchor pull-out capacity by soil mechanics principles is inadequate, and that there is a need for the standardization of test procedures and soil classification and for further test data. Suggestions for future research are presented.
BSS115. Fire safety for high-rise buildings: The role of commu
nications, R. A. Glass and A. I. Rubin, Nat. Bur. Stand. (U.S.), Bldg. Sci. Ser. 115, 47 pages (Apr. 1979) SN003-00302016-8.
BSS75. Building research at the National Bureau of Standards
1968-1974, N. Gallagher, Ed., Nat. Bur. Stand. (U.S.), Bldg. Sci. Ser. 75, 126 pages (Mar. 1979) SN003-003-02029-0.
Key words: building technology; Center for Building
Technology; history of building research. This report details the progress of building research at the Center for Building Technology from the year 1968 to 1974. Starting with the backlog of needed research in building techniques, components, and materials that faced researchers in the 60's, this history covers the evolution of the performance concept for building specifications, cooperation with states and codes-generating organizations, and specific technical accomplishments. The report continues with discussions of programs involving the building community, research on the needs of the building users, and technology transfer. A special chapter is devoted to energy conservation in buildings and how CBT's test methods and other programs—including solar-were pressed into this vital national struggle.
BSS95. The development of an improved compression test
method for wall panels, C. W. C. Yancey and L. E. Cattaneo, Nar. Bur. Stand. (U.S.), Bldg. Sci. Ser. 95, 108 pages (Feb. 1979) SN003-003-01697-7.
Key words: buildings; communications systems; fire safety;
high-rise; model codes; people movement; systems design. This literature survey reviews the communications requirements for fire safety in buildings from the standpoint of the building occupant and the control operator. It traces the development of the problem of communications in buildings and the specialized needs that exist today.
An examination is made of the purposes of a communications system in buildings as well as some of the psychological design requirements necessary for such a system.
The communications requirements of the building occupants are also covered, with emphasis on the types of information communicated by signals and the integration of those signals into an overall system design.
Personnel requirements for staffing a control center are also discussed, along with common problems in several operational communications systems.
Detailed examples of communications systems are provided. Portions of several model codes which cover communications systems are presented. Suggested areas for future research on fire safety in buildings are identified.
BSSI 17. Experimental verification of a standard test procedure
for solar collectors, J. E. Hill, J. P. Jenkins, and D. E. Jones, Nat. Bur. Stand. (U.S.), Bldg. Sci. Ser. 117, 126 pages (Jan. 1979) SN003-003-02008-7.
Key words: compression; eccentric loading; flat-end; kern;
loading rate; pin-end; test method; wall panels; walls. An experimental and analytical investigation of the primary factors involved in the testing of prototype wall panels under axial compression loading is reported. The objective of the investigation was to develop a method of testing wall specimens that incorporates the best features of ASTM Standard Method E 72 while at the same time incorporating improvements in the areas of deficiency in the Standard. Twenty-five laboratory tests were conducted on samples composed of five types of wall panel construction. The panels were tested to failure under either of two different eccentricities of load, while being supported with one of two types of idealized end conditions. Selected test results and detailed descriptions of the laboratory procedures used are presented. A computer-aided analytical study of the variables affecting the degree of uniformity of loading was conducted. Equations based on the analogy of beams supported on elastic foundations were used in the analysis. A study of the statistical parameters commonly used to interpret test results was conducted to establish useful guidelines for predicting structural performance on the basis of small sample test results. A compression test method applicable to traditional and innovative wall constructions is presented. The principal additions in the revised test method are as follows: (a) a provision for variable eccentricity, (b) a procedure for selecting a load distribution assembly which will be compatible with the test-panel.
Key words: measurement; solar collector; solar energy;
solar radiation; standards, standard test; testing. A proposed procedure for testing and rating solar collectors based on thermal performance was published by the National Bureau of Standards (NBS) in 1974. Subsequently, the American Society of Heating, Refrigerating, and Air Conditioning (ASHRAE) developed a modified version of the NBS procedure which was adopted in early 1977 as ASHRAE Standard 93-77. A test facility for water-heating and air-heating collectors has been built at NBS and was used to support the development of Standard 93-77. The purpose of this report is to describe the recently adopted test procedure, the NBS test facility, and the tests that were conducted to support the development of the procedure.
BSS107. Soil and rock anchors for mobile homes-A state-of
the-art report, W. D. Kovacs and F. Y. Yokel, Nat. Bur. Stand. (U.S.), Bldg. Sci. Ser. 107, 164 pages (Oct. 1979) SN003-003-02121-1.
BSS118. Extreme wind speeds at 129 stations in the contiguous
United States, E. Simiu, M. J. Changery, and J. J. Filliben, Nat. Bur. Stand. (U.S.), Bldg. Sci. Ser. 118, 318 pages (Mar. 1979) SN003-003-02041-9.