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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Concepts for improving the damage tolerance of composite compression panels

The results of an experimental evaluation of graphite-epoxy composite compression panel impact damage tolerance and damage propagation arrest concepts are reported. The tests were conducted on flat plate specimens and blade-stiffened structural panels such as those used in commercial aircraft wings, and the residual strength of damaged specimens and their sensitivity to damage while subjected to in-plane compression loading were determined. Results suggest that matrix materials that fail by delamination have the lowest damage tolerance, and it is concluded that alternative matrix materials with transverse reinforcement to suppress the delamination failure mode and yield the higher-strain value transverse shear crippling mode should be developed.

Rhodes, M. D.↗
NASA NTRS1980

Mesoscale damage patterns of Hurricane Frederic in relation to enhanced SMS imagery

An F-scale analysis of Hurricane Frederic (September 12 and 13, 1979) was performed in order to determine the structural damage patterns attributed to the storm. Enhanced SMS imagery revealed patterns of mesoscale features as well as features related to the shielding effects of trees and the grouping effect of structures. The scatter in estimating the damage scale was + or - 1 F-scale. It is shown that discrepancies in recorded wind speed and the estimated wind-speed from the F-scale are the result of different damage mechanisms of hurricane and tornado winds. Radar echoes revealed that the structure of Hurricane Frederic changed from an axisymmetric center to an instantaneous center of rotation. Finally, it is suggested that major hurricane wind and water damage be investigated in greater detail by aerial photography, damage vector mapping, and ground surveys.

Fujita, T. T.↗
NASA NTRS1982

Initial stages of cavitation damage and erosion on copper and brass tested in a rotating disk device

In view of the differences in flow and experimental conditions, there has been a continuing debate as to whether or not the ultrasonic method of producing cavitation damage is similar to the damage occurring in cavitating flow systems, namely, venturi and rotating disk devices. In this paper, the progress of cavitation damage during incubation periods on polycrystalline copper and brass tested in a rotating disk device is presented. The results indicate several similarities and differences in the damage mechanism encountered in a rotating disk device (which simulates field rotary devices) and a magnetostriction apparatus. The macroscopic erosion appears similar to that in the vibratory device except for nonuniform erosion and apparent plastic flow during the initial damage phase.

Rao, P. V.↗
NASA NTRS1982

The damage equivalence of electrons, protons, and gamma rays in MOS devices

The results of laboratory tests to determine the radiation damage effects induced on MOS devices from Co-60, electron, and proton radiation are reported. The tests are performed to establish the relationship between the Co-60 gamma rays and the level of damage to the MOS devices in regards to different damages which can be expected with the electron and particle bombardments experienced in space applications. CMOS devices were exposed to the Co-60 gamma rays, 1 MeV electrons, and 1 MeV protons while operating at 3, 10, and 15 V. The test data indicated that the Co-60 source was reliable for an initial evaluation of the electron damages up to 2 MeV charge. A correction factor was devised for transferring the Co-60 measurements to proton damages, independent of bias and transistor types, for any orbit or environment.

Brucker, G. J.↗
NASA NTRS1984

Concepts for improving the damage tolerance of composite compression panels

The residual strength of specimens with damage and the sensitivity to damage while subjected to an applied inplane compression load were determined for flatplate specimens and blade-stiffened panels. The results suggest that matrix materials that fail by delamination have the lowest damage tolerance capability. Alternate matrix materials or laminates which are transversely reinforced suppress the delamination mode of failure and change the failure mode to transverse shear crippling which occurs at a higher strain value. Several damage-tolerant blade-stiffened panel design concepts are evaluated. Structural efficiency studies conducted show only small mass penalties may result from incorporating these damage-tolerant features in panel design. The implication of test results on the design of aircraft structures was examined with respect to FAR requirements.

Rhodes, M. D.↗
NASA NTRS1984

Tensile strength of composite sheets with unidirectional stringers and crack-like damage

The damage tolerance characteristics of metal tension panels with riveted and bonded stringers are well known. The stringers arrest unstable cracks and retard propagation of fatigue cracks. Residual strengths and fatigue lives are considerably greater than those of unstiffened or integrally stiffened sheets. The damage tolerance of composite sheets with bonded composite stringers loaded in tension was determined. Cracks in composites do not readily propagate in fatigue, at least not through fibers. Moreover, the residual strength of notched composites is sometimes even increased by fatigue loading. Therefore, the residual strength aspect of damage tolerance, and not fatigue crack propagation, was investigated. About 50 graphite/epoxy composite panels were made with two sheet layups and several stringer configurations. Crack-like slots were cut in the middle of the panels to simulate damage. The panels were instrumented and monotonically loaded in tension to failure. The tests indicate that the composite panels have considerable damage tolerance, much like metal panels. The stringers arrested cracks that ran from the crack-like slots, and the residual strengths were considerably greater than those of unstiffened composite sheets. A stress intensity factor analysis was developed to predict the failing strains of the stiffened panels. Using the analysis, a single design curve was produced for composite sheets with bonded stringers of any configuration.

Poe, C. C., Jr.↗
NASA NTRS1985

Reexamination of Cumulative Fatigue Damage Laws

Treatment of accumulated fatigue damage in materials and structures subjected to a history of nonsimple repetitive loadings has received a large amount of attention in recent years. A method used for the treatment of complex loading is known as linear damage rule. It was recognized that, this method could result in unconservative predictions of material and structural behavior. An intense flurry of activity followed in the pursuit of alternative methods of analysis that would predict behavior more accurately. So many methods were introduced that it became necessary periodically to prepare review papers placing all the new methods into perspective. The current integrated view regarding the state of the art as it applies to this effort is discussed. The more recently proposed cumulative damage life prediction methods are reviewed. The double linear damage rule (DLDR), which has evolved over the past 20 years, is reexamined with the intent of improving its accuracy and applicability to engineering problems. Modifications are introduced to the analytical formulation to achieve greater compatibility between the DLDR and the so-called damage curve approach, which is an alternative continuous representation of the DLDR.

Halford, G. R.↗
NASA NTRS1985

Influence of interface ply orientation on fatigue damage of adhesively bonded composite joints

An experimental study of cracked-lap-shear specimens was conducted to determine the influence of adherend stacking sequence on debond initiation and damage growth in a composite-to-composite bonded joint. Specimens consisted of quasi-isotropic graphite/epoxy adherends bonded together with either FM-300 or EC 3445 adhesives. The stacking sequence of the adherends was varied such that 0 deg, 45 deg, or 90 deg plies were present at the adherend-adhesive interfaces. Fatigue damage initiated in the adhesive layer in those specimens with 0 deg nd 45 deg interface plies. Damage initiated in the form of ply cracking in the strap adherend for the specimens with 90 deg interface plies. The fatigue-damage growth was in the form of delamination within the composite adherends for specimens with the 90 deg and 45 deg plies next to the adhesive, while debonding in the adhesive resulted for the specimens with 0 deg plies next to the adhesive. Those joints with the 0 deg and 45 deg plies next to either adhesive has essentially the same fatigue-damage-initiation stress levels. These stress levels were 13 and 71 percent higher, respectively, than those for specimens with 90 deg plies next to the EC 3445 and FM-300 adhesives.

Johnson, W. S.↗
NASA NTRS1983

The strainrange conversion principle for treating cumulative fatigue damage in the creep range

A formula is derived for combining effects of successive hysteresis loops in the creep range of materials when one loop has excess tensile creep, while the other contains excess compressive creep. The resultant effect resembles single loops involving balanced tensile and compressive creep. The attempt to use the Interaction Damage Rule as a tool in combining loops of non-equal size and complex strainrange content has led to important new concepts useful in future studies of creep-fatigue. It turns out that the Interaction Damage Rule is basically an expression of how a set of hysteresis loops involving only single generic strains can combine to produce the same micromechanistic damage as the loop containing the combined strainranges which it analyzes. Making use of the underlying concept of Strainrange Partitioning that only the strainrange content of a hysteresis loop governs fatigue life, not order of introducing strainranges, a rational derivation of the Interaction Damage Rule is provided, showing also how it can effectively be used to synthesize independent loops and determine both damaging and healing effects.

Manson, S. S.↗
NASA NTRS1984

A history dependent damage model for low cycle fatigue

This paper examines damage assessment and accumulation. A nonlinear damage postulate is advanced that embodies the dependence of the damage rate on cycle-dependent changes in the bulk microstructure and the surface topography. The postulate is analytically formulated in terms of the deformation history dependence of the bulk behavior. This formulation is used in conjunction with baseline data in accordance with the damage postulate to predict the low cycle fatigue resistance of OFE copper. Close comparison of the predictions with observed behavior suggests the postulate offers a viable basis for nonlinear damage analysis.

Leis, B. N.↗
NASA NTRS1985

Damage initiation at curved free edges - Application to uniaxially loaded plates containing holes and notches

The concept which imputes initial free edge interlaminar damage to the differences in material properties among adjacent laminae, formerly applied to straight free edges, is presently extended to the case of curved free edges through interpretation in terms of differences in the shear and elongation strains among adjacent laminae. Attention is given to both material property differences and laminate strain spatial distributions at the hole edge. Since a large strain level and a small difference in material properties are found to be as damaging as a small strain and large difference, interlaminar damage will probably begin at a circumferential location other than the net section. These findings are further explored in view of a second extension, using the edges replication technique to record damage at a curved free edge. The damage recorded for uniaxially loaded plates with central circular holes and semicircular edge notches are compared with difference theory predictions.

Klang, E. C.↗
NASA NTRS1985

Depletion layer recombination effects on the radiation damage hardness of gallium arsenide cells

The significant effect of junction depletion layer recombination on the efficiency of windowed GaAs cells was demonstrated. The effect becomes more pronounced as radiation damage occurs. The depletion is considered for 1 MeV electron fluences up to 10 to the 16th power e/sq m. The cell modeling separates damage in emitter and base or buffer layers using different damage coefficients is reported. The lower coefficient for the emitter predicts less loss of performance at fluences greater than 10 to the 15th power e/sq cm. A method for obtaining information on junction recombination effects as damage proceeds is described; this enables a more complete diagnosis of damage to be made.

Garlick, G. F. J.↗
NASA NTRS1983

Nonlinear damage analysis: Postulate and evaluation

The objective of this program is to assess the viability of a damage postulate which asserts that the fatigue resistance curve of a metal is history dependent due to inelastic action. The study focusses on OFE copper because this simple model material accentuates the inelastic action central to the damage postulate. Data relevant to damage evolution and crack initiation are developed via a study of surface topography. The effects of surface layer residual stresses are explored via comparative testing as were the effects in initial prestraining. The results of the study very clearly show the deformation history dependence of the fatigue resistance of OFE copper. Furthermore the concept of deformation history dependence is shown to qualitatively explain the fatigue resistance of all histories considered. Likewise quantitative predictions for block cycle histories are found to accurately track the observed results. In this respect the assertion that damage per cycle for a given level of the damage parameter is deformation history dependent appears to be physically justified.

Leis, B. N.↗
NASA NTRS1984

Durability and damage tolerance of Large Composite Primary Aircraft Structure (LCPAS)

Analysis and testing addressing the key technology areas of durability and damage tolerance were completed for wing surface panels. The wing of a fuel-efficient, 200-passenger commercial transport airplane for 1990 delivery was sized using graphite-epoxy materials. Coupons of various layups used in the wing sizing were tested in tension, compression, and spectrum fatigue with typical fastener penetrations. The compression strength after barely visible impact damage was determined from coupon and structural element tests. One current material system and one toughened system were evaluated by coupon testing. The results of the coupon and element tests were used to design three distinctly different compression panels meeting the strength, stiffness, and damage-tolerance requirements of the upper wing panels. These three concepts were tested with various amounts of damage ranging from barely visible impact to through-penetration. The results of this program provide the key technology data required to assess the durability and damage-tolerance capability or advanced composites for use in commercial aircraft wing panel structure.

Mccarty, John E.↗
NASA NTRS1987

Shuttle/Centaur G-prime composite adapters damage tolerance/repair test program

The Space Shuttle/Centaur Composite Adapters Damage Tolerance/Repair Test program had as its goals the determination of probable and potentially critical defects or damages on the adapters' strength and stability, as well as the adequacy of repairs on significantly damaged areas and the generation of NDT data for the upgrading of acceptance criteria. Such rational accept/reject criteria and repair methods reduce both engineering liason costs and any unnecessary parts-scrapping. Successful 'damage tolerant' design ensures that degradations of strength and stability due to undetected defects or damage will not be catastrophic.

Sollars, Teresa A.↗
NASA NTRS1988

Fatigue testing and damage development in continuous fiber reinforced metal matrix composites

A general overview of the fatigue behavior of metal matrix composites (MMC) is presented. The first objective is to present experimental procedures and techniques for conducting a meaningful fatigue test to detect and quantify fatigue damage in MMC. These techniques include interpretation of stress-strain responses, acid etching of the matrix, edge replicas of the specimen under load, radiography, and micrographs of the failure surfaces. In addition, the paper will show how stiffness loss in continuous fiber reinforced metal matrix composites can be a useful parameter for detecting fatigue damage initiation and accumulation. Second, numerous examples of how fatigue damage can initiate and grow in various MMC are given. Depending on the relative fatigue behavior of the fiber and matrix, and the interface properties, the failure modes of MMC can be grouped into four categories: (1) matrix dominated, (2) fiber dominated, (3) self-similar damage growth, and (4) fiber/matrix interfacial failures. These four types of damage will be discussed and illustrated by examples with the emphasis on the fatigue of unnotched laminates.

Johnson, W. S.↗
NASA NTRS1988

Assessing forest damage in high-elevation coniferous forests in Vermont and New Hampshire using Thematic Mapper data

This study evaluates the potential of measuring/mapping forest damage in spruce-fir forests in the Green Mountains of Vermont and White Mountains of New Hampshire using Landsat Thematic Mapper (TM) data. The TM 1.65/0.83-micron (TM5/4) and 2.22/0.83-micron (TM7/4) band ratios were found to correlate well with ground-based measurements of forest damage (a measure of percentage foliar loss) at 11 spruce-fir stands located on Camels Hump, a mountain in northern Vermont. Images using 0.56 and 1.65-micron bands with 1.65/0.83-micron band ratios indicated locations of heavy conifer forest damage. Both 1.65/0.83 and 2.22/0.83-micron band ratios were used to quantify levels of conifer forest damage among individual mountains throughout many of the Green and White Mountains. Damage was found to be consistently higher for the Green than the White Mountains.

Vogelmann, James E.↗
NASA NTRS1988

Design, testing, and damage tolerance study of bonded stiffened composite wing cover panels

Results are presented from the application of damage tolerance criteria for composite panels to multistringer composite wing cover panels developed under NASA's Composite Transport Wing Technology Development contract. This conceptual wing design integrated aeroelastic stiffness constraints with an enhanced damage tolerance material system, in order to yield optimized producibility and structural performance. Damage tolerance was demonstrated in a test program using full-sized cover panel subcomponents; panel skins were impacted at midbay between stiffeners, directly over a stiffener, and over the stiffener flange edge. None of the impacts produced visible damage. NASTRAN analyses were performed to simulate NDI-detected invisible damage.

Madan, Ram C.↗