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At least 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Composite ingot casting

A method and system for continuously or semicontinuously casting a composite metal article, such as a structurally composite ingot or the like, wherein one of the principal structural components of the ingot comprises an aluminum-lithium alloy. During such casting by a D.C. (direct chill) conventional tubular mold or electromagnetic process, the aluminum-lithium structural component of a structurally composite ingot is encircled or peripherally encased by a· further outer metal cladding component that can be cast simultaneously with the aluminum-lithium component such as another outer aluminous alloy from which lithium is absent as a constituent or impurity, although it may be present and tolerated as a trace element. In this arrangement the aluminum-lithium structural component is prevented during casting from coming into direct contact with the chilling coolant, normally water, with which lithium can react violently. Only the outer aluminous alloy envelope is subjected to the direct contact of a liquid coolant whereby as it solidifies, this outer envelope or . peripheral sheath acts as an impervious secondary mold for and protects the inner aluminum--lithium alloy structural component which is then directly controllably chilled and solidified.

George J Binczewski↗
NASA NTRS1991

Progressive fracture in composites subjected to hygrothermal environment

The influence of hygrothermal environmental conditions on the load carrying ability and response of composite structures are investigated via computational simulation. An integral computer code is utilized for the simulation of composite structural degradation under loading. Damage initiation, damage growth, fracture progression, and global structural fracture are included in the simulation. Results demonstrate the significant hygrothermal effects on composite structural response, toughness, and durability.

Minnetyan, Levon↗
NASA NTRS2005

Computational Simulation of Damage Propagation in Three-Dimensional Woven Composites

Three dimensional (3D) woven composites have demonstrated multi-directional properties and improved transverse strength, impact resistance, and shear characteristics. The objective of this research is to develop a new model for predicting the elastic constants, hygrothermal effects, thermomechanical response, and stress limits of 3D woven composites; and to develop a computational tool to facilitate the evaluation of 3D woven composite structures with regard to damage tolerance and durability. Fiber orientations of weave and braid patterns are defined with reference to composite structural coordinates. Orthotropic ply properties and stress limits computed via micromechanics are transformed to composite structural coordinates and integrated to obtain the 3D properties. The various stages of degradation, from damage initiation to collapse of structures, in the 3D woven structures are simulated for the first time. Three dimensional woven composite specimens with various woven patterns under different loading conditions, such as tension, compression, bending, and shear are simulated in the validation process of this research. Damage initiation, growth, accumulation, and propagation to fracture are included in these simulations.

Huang, Dade↗
NASA NTRS1995

Lightweight Composite Intertank Structure

Report presents results of study for proposed lightweight composite material alternative to present semimonocoque aluminum intertank structure for advanced launch vehicles. Proposed structure integrated assembly of sandwich panels made of laminated epoxy-matrix/carbon-fiber skins, and aluminum honeycomb core.

Mehle, Greg V.↗
NASA NTRS1990

Progression of damage and fracture in composites under dynamic loading

A new computational simulation method is presented to evaluate the dynamic aspects of composite structural response and durability that could not be simulated previously. Composite structural behavior under any loading, geometry, composite system, laminate configuration, and boundary conditions can now be simulated. Structural degradation, delamination, fracture, and damage propagation are included in the simulation. An angle-plied composite plate structure under normal impact loading is used as an example to demonstrate the versatility of the simulation method.

Minnetyan, Levon↗
NASA NTRS2015

Unibody Composite Pressurized Structure (UCPS) for In-Space Propulsion

Microcosm, Inc., in conjunction with the Scorpius Space Launch Company, is developing a UCPS (Unibody Composite Pressurized Structure )for in-space propulsion. This innovative approach constitutes a clean break from traditional spacecraft design by combining what were traditionally separate primary and secondary support structures and metal propellant tanks into a single unit.

Rufer, Markus↗
NASA NTRS1998

Health Monitoring of Composite Material Structures Using a Vibrometry Technique

Non-destructive evaluation (NDE) methods for quantifying and locating damage are essential for inspecting structures to ensure safety and reliability. Transmittance function monitoring is a potentially new NDE technique being tested as a tool to detect, quantify, and locate damage on flexible structures. The technique has a large spatial range that is practical for detecting damage on large composite material structures such as a reusable launch vehicle. The Transmittance Function (TF) theory is based on structural dynamics principles that define how vibration at one point in a structure is related to a force at another point. This relationship is called the Frequency Response Function (FRF). A Transmittance Function (TF) is derived as the ratio of FRFs, and can detect damage because the FRFs change due to damage. If one excitation is used for the testing, the force does not need to be measured to compute the TF. In the damage detection procedure, the structure is subjected to wide-band vibration and TFs are computed between different accelerometers to detect changes in the structure, presumably due to damage. In the first year of the project the TF method was tested on a bolted panel, a curved panel, and beams, all made of fiberglass. It was shown that damage could be detected using low frequency vibration, 250 to 1,250 Hz. The technique is sensitive to damage, but it requires storage of historical or pre-damage TFs for the healthy structure. This would become a large data storage requirement for large structures. Thus one objective for the second year of the project was to eliminate the need to store historical data. The second year report gives details of how storage of historical data was eliminated. Further results of testing panel structures are also given.

Schulz, Mark J.↗
NASA NTRS2008

Probabilistic Methods for Structural Reliability and Risk

A probabilistic method is used to evaluate the structural reliability and risk of select metallic and composite structures. The method is a multiscale, multifunctional and it is based on the most elemental level. A multi-factor interaction model is used to describe the material properties which are subsequently evaluated probabilistically. The metallic structure is a two rotor aircraft engine, while the composite structures consist of laminated plies (multiscale) and the properties of each ply are the multifunctional representation. The structural component is modeled by finite element. The solution method for structural responses is obtained by an updated simulation scheme. The results show that the risk for the two rotor engine is about 0.0001 and the composite built-up structure is also 0.0001.

Chamis, Christos C.↗
NASA NTRS2010

Probabilistic Methods for Structural Reliability and Risk

A probabilistic method is used to evaluate the structural reliability and risk of select metallic and composite structures. The method is a multiscale, multifunctional and it is based on the most elemental level. A multifactor interaction model is used to describe the material properties which are subsequently evaluated probabilistically. The metallic structure is a two rotor aircraft engine, while the composite structures consist of laminated plies (multiscale) and the properties of each ply are the multifunctional representation. The structural component is modeled by finite element. The solution method for structural responses is obtained by an updated simulation scheme. The results show that the risk for the two rotor engine is about 0.0001 and the composite built-up structure is also 0.0001.

Chamis, Christos C.↗
NASA NTRS1990

Progression of damage and fracture in composites under dynamic loading

A new computational simulation method is presented to evaluate the dynamic aspects of composite structural response and durability that have not been simulated previously. Composite structural behavior under any loading condition, geometry, composite system, laminate configuration, and boundary conditions can now be simulated. Structural degradation, delamination, fracture, and damage propagation are included in the simulation. An angle-plied composite plate structure under normal impact loading is used as an example to demonstrate the versatility of the simulation method.

Minnetyan, Levon↗
NASA NTRS1974

An investigation of the structure and composition of the solar atmosphere using X-ray and EUV spectra obtained with the OV1-17 and OSO-4 and OSO-5 satellites

Studies of the structure and composition of the solar corona were undertaken, using a number of satellite observations of the coronal X-ray spectrum. A systematic technique was developed to carry out the required analysis, and the analytical techniques available to calculate the coronal spectrum have been developed and improved. A review of other analyses of solar coronal structure is also included.

Walker, A. B. C., Jr.↗
NASA NTRS2015

An Analysis Methodology to Predict Damage Propagation in Notched Composite Fuselage Structures

A new methodology is proposed for predicting damage propagation in notched composite skin-stiffened structures. The proposed approach considers the interaction of damage propagation in the skin with delamination of the stiffener in order to assess the damage containment behavior of the structure. The damage propagating from a notch within a thin fiber-reinforced polymer skin is idealized as a through-the-thickness cohesive crack. The cohesive law for the through-the-thickness crack is characterized using a compact tension test. The approach was applied to a full-scale pultruded rod stitched efficient unitized structure (PRSEUS) concept fuselage panel that was tested recently. The stitched skin/stringer interfaces, a key feature of the PRSEUS concept, were modeled to assess the effectiveness of the stitching at containing damage propagation. Comparison between the predicted and observed damage extension shows acceptable agreement throughout loading. These results indicate that the model can represent accurately the complex interactions between a through-the-thickness crack in the skin and delamination between the skin and stringer. The model is used to demonstrate that the skin-stiffener interface toughness is critical to damage containment capability

Bergan, A.↗
NASA NTRS1985

The Structure and Composition of Uranus and Neptune

Uranus and Neptune form a special class of planetary objects; intermediate in mass and composition between the giant Hydrogen-rich planets, Jupiter and Saturn, and the small, rocky terrestrial planets. Their structure and composition are not only of intrinsic importance, but also should provide information as to the nature of the protoplanetary nebula and the processes of planetary formation. A detailed set of theoretical models of these planets within the framework of two and three shell models was constructed. The ratio of ice to rock (1/r) is varied. The three shell model fits the data on the two planets best.

Reynolds, R. T.↗
NASA NTRS1988

Nondestructive evaluation by acousto-ultrasonics

Acousto-ultrasonics is an ultrasonic technique that was originally devised to cope with the particular problems associated with nondestructive evaluation (NDE) of fiber/polymer composite structures. The fiber/polymer composites are more attenuating to ultrasound than any other material presently of interest. This limits the applicability of high-frequency ultrasonics. A common use of ultrasound is the imaging of flaws internal to a structure by scattering from the interface with the flaw. However, structural features of composites can scatter ultrasound internally, thus obscuring the flaws. A need relative to composites is to be able to nondestructively measure the strength of laminar boundaries in order to assess the integrity of a structure. Acousto-ultrasonics has exhibited the ability to use the internal scattering to provide information for determining the strength of laminar boundaries. Analysis of acousto-ultrasonic signals by the wave ray paths that compose it leads to waveform partitioning that enhances the sensitivity to mechanical strength parameters.

Kautz, Harold E.↗
NASA NTRS1983

A Study of Production of Miscibility Gap Alloys with Controlled Structures

Composite materials were directionally solidified using a new technique to align the constituents longitudinally along the length of the specimen. In some instances a tin coating was applied and diffused into the sample to form a high transition temperature superconducting phase. The superconducting properties were measured and compared with the properties obtained for powder composites and re-directionally solidified powder compacts. The samples which were compacted and redirectionally solidified showed the highest transition temperature and wildest transition range. This indicates that both steps, powder compaction and resolidification, determine the final superconducting properties of the material.

Parr, R. A.↗
NASA NTRS2011

Evaluation of Lightning Induced Effects in a Graphite Composite Fairing Structure

Defining the electromagnetic environment inside a graphite composite fairing due to lightning is of interest to spacecraft developers. This paper is the first in a two part series and studies the shielding effectiveness of a graphite composite model fairing using derived equivalent properties. A frequency domain Method of Moments (MoM) model is developed and comparisons are made with shielding test results obtained using a vehicle-like composite fairing. The comparison results show that the analytical models can adequately predict the test results. Both measured and model data indicate that graphite composite fairings provide significant attenuation to magnetic fields as frequency increases. Diffusion effects are also discussed. Part 2 examines the time domain based effects through the development of a loop based induced field testing and a Transmission-Line-Matrix (TLM) model is developed in the time domain to study how the composite fairing affects lightning induced magnetic fields. Comparisons are made with shielding test results obtained using a vehicle-like composite fairing in the time domain. The comparison results show that the analytical models can adequately predict the test and industry results.

Trout, Dawn H.↗
NASA NTRS2011

Evaluation of Lightning Induced Effects in a Graphite Composite Fairing Structure

Defining the electromagnetic environment inside a graphite composite fairing due to near-by lightning strikes is of interest to spacecraft developers. This effort develops a transmission-line-matrix (TLM) model with a CST Microstripes to examine induced voltages. on interior wire loops in a composite fairing due to a simulated near-by lightning strike. A physical vehicle-like composite fairing test fixture is constructed to anchor a TLM model in the time domain and a FEKO method of moments model in the frequency domain. Results show that a typical graphite composite fairing provides adequate shielding resulting in a significant reduction in induced voltages on high impedance circuits despite minimal attenuation of peak magnetic fields propagating through space in near-by lightning strike conditions.

Trout, Dawn H.↗