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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

An in-situ measurement of particulates from solid rocket motors fired in space

Current models exist that predict the damage caused by the impact of aluminum oxide exhaust particles as well as their lifetime in useable space. In these models, two necessary inputs are the size and flux of the particles. An experiment, referred to as the Plume Witness Plate, was designed for the Remote Manipulator System of the space shuttle orbiter to measure in-situ the flux and material effects of a solid rocket motor (SRM) firing in space. Five different types of samples were used to provide a broad range of substances: (1) fused quartz glass (representative of orbiter windows); (2) germanium micrometeroid capture cells; (3) orbiter HRTS tiles from the thermal protection system; (4) Kapton foil; and (5) metallic disks of aluminum, copper, titanium, graphite epoxy, and gold. The analyses of the data show excellent agreement with ground-based SRM firings in terms of particle size distribution and mass distribution. The Particle Impact Damage Integrator computer model used to calculate potential damage of orbiter surfaces by SRM exhaust plumes agrees favorable with the results in terms of particle size and velocity distributions though it may be conservative by as much as 20%.

Alred, J. W.↗
NASA NTRS1985

Fatigue cracking of aluminum under spectrum loading at various humidities

The effect of moisture on Stage I fatigue in aluminum was studied under constant amplitude loading and under a severe log-normal spectrum loading. Crack initiation and early crack growth was monitored using accurate specimen compliance measurements statistically generated using computer-aided data acquisition and analysis. Fatigue strength in aluminum was found to be greatly reduced by humidity under both constant amplitude and log-normal spectrum loading. Use of Miner's theory of cumulative damage to predict the outcome of the spectrum tests, given the results of the constant amplitude tests, was investigated. A systematic pattern of deviation from Miner's theory was found, which was also a function of the humidity level.

Chappell, D. P.↗
NASA NTRS1987

Strength of a thick graphite/epoxy rocket motor case after impact by a blunt object

The National Aeronautics and Space Administration is developing graphite/epoxy filament-wound cases (FWC) for the solid rocket motors of the Space Shuttle. The membrane region is about 36 mm thick. A study was made to determine the reduction in strength of the FWC due to accidental damage caused by low-velocity impacts. Two 76.2 cm diameter by 30.5 cm long cylinders were impacted every 5 cm of circumference with 1.27 cm radius impacters of various mass. The impacters represented tools and equipment dropped from various heights. One cylinder was empty and the other was filled with inert propellant. Five cm wide test specimens were cut from the cylinder. Each was centered on an impact sight. The specimens were X-rayed and loaded to failure in uniaxial tension. The strengths and depths of impact damage were analyzed in terms of maximum impact force. Rigid body mechanics and the Hertz law were used to derive an equation for impact force in terms of kinetic energy and the masses of the impacter and target. The depth of damage was predicted in terms of impact force using Love's solution of pressure applied on part of the boundary of a semi-infinite body.

Poe, C. C., Jr.↗
NASA NTRS1988

Environment assisted degradation mechanisms in advanced light metals

The general goals of the research program are to characterize alloy behavior quantitatively and to develop predictive mechanisms for environmental failure modes. Successes in this regard will provide the basis for metallurgical optimization of alloy performance, for chemical control of aggressive environments, and for engineering life prediction with damage tolerance and long term reliability.

Gangloff, Richard P.↗
NASA NTRS1989

Environment assisted degradation mechanisms in advanced light metals

A multifaceted research program on the performance of advanced light metallic alloys in aggressive aerospace environments, and associated environmental failure mechanisms was initiated. The general goal is to characterize alloy behavior quantitatively and to develop predictive mechanisms for environmental failure modes. Successes in this regard will provide the basis for metallurgical optimization of alloy performance, for chemical control of aggressive environments, and for engineering life prediction with damage tolerance and long term reliability.

Gangloff, R. P.↗
NASA NTRS1989

Strength of a thick graphite/epoxy rocket motor case after impact by a blunt object

The National Aeronautics and Space Administration is developing graphite/epoxy filament-wound cases (FWC) for the solid rocket motors of the Space Shuttle. The membrane region is about 36 mm thick. A study was made to determine the reduction in strength of the FWC due to accidental damage caused by low-velocity impacts. Two 76.2 cm diameter by 30.5 cm long cylinders were impacted every 5 cm of circumference with 1.27 cm radius impacters of various mass. The impacters represented tools and equipment dropped from various heights. One cylinder was empty and the other was filled with inert propellant. Five cm wide test specimens were cut from the cylinder. Each was centered on an impact site. The specimens were X-rayed and loaded to failure in uniaxial tension. The strengths and depths of impact damage were analyzed in terms of maximum impact force. Rigid body mechanics and the Hertz law were used to derive an equation for impact force in terms of kinetic energy and the masses of the impacter and target. The depth of damage was predicted in terms of impact force using Love's solution of pressure applied on part of the boundary of a semi-infinite body.

Poe, Clarence C., Jr.↗
NASA NTRS1993

Thermal stress analysis of composites in the space environment

A finite element micromechanics approach was utilized to investigate the thermally induced stress fields in continuous fiber reinforced polymer matrix composites at temperatures typical of spacecraft operating environments. The influence of laminate orientation was investigated with a simple global/local formulation. Thermal stress calculations were used to predict probable damage initiation locations, and the results were compared to experimentally observed damage in several epoxy matrix composites. The influence of an interphase region on the interfacial stress states was investigated.

Bowles, David E.↗
NASA NTRS1999

Progressive Failure Analysis Methodology for Laminated Composite Structures

A progressive failure analysis method has been developed for predicting the failure of laminated composite structures under geometrically nonlinear deformations. The progressive failure analysis uses C(exp 1) shell elements based on classical lamination theory to calculate the in-plane stresses. Several failure criteria, including the maximum strain criterion, Hashin's criterion, and Christensen's criterion, are used to predict the failure mechanisms and several options are available to degrade the material properties after failures. The progressive failure analysis method is implemented in the COMET finite element analysis code and can predict the damage and response of laminated composite structures from initial loading to final failure. The different failure criteria and material degradation methods are compared and assessed by performing analyses of several laminated composite structures. Results from the progressive failure method indicate good correlation with the existing test data except in structural applications where interlaminar stresses are important which may cause failure mechanisms such as debonding or delaminations.

Sleight, David W.↗
NASA NTRS2003

Test-Free Fracture Toughness

Computational simulation results can give the prediction of damage growth and progression and fracture toughness of composite structures. The experimental data from literature provide environmental effects on the fracture behavior of metallic or fiber composite structures. However, the traditional experimental methods to analyze the influence of the imposed conditions are expensive and time consuming. This research used the CODSTRAN code to model the temperature effects, scaling effects and the loading effects of fiberbraided composite specimens with and without fiber-optic sensors on the damage initiation and energy release rates. The load-displacement relationship and fracture toughness assessment approach is compared with the test results from literature and it is verified that the computational simulation, with the use of established material modeling and finite element modules, adequately tracks the changes of fracture toughness and subsequent fracture propagation for any fiberbraided composite structure due to the change of fiber orientations, presence of large diameter optical fibers, and any loading conditions.

Minnetyan, Levon↗
NASA NTRS2003

Test-Free Fracture Toughness

Computational simulation results can give the prediction of damage growth and progression and fracture toughness of composite structures. The experimental data from literature provide environmental effects on the fracture behavior of metallic or fiber composite structures. However, the traditional experimental methods to analyze the influence of the imposed conditions are expensive and time consuming. This research used the CODSTRAN code to model the temperature effects, scaling effects and the loading effects of fiber/braided composite specimens with and without fiber-optic sensors on the damage initiation and energy release rates. The load-displacement relationship and fracture toughness assessment approach is compared with the test results from literature and it is verified that the computational simulation, with the use of established material modeling and finite element modules, adequately tracks the changes of fracture toughness and subsequent fracture propagation for any fiber/braided composite structure due to the change of fiber orientations, presence of large diameter optical fibers, and any loading conditions.

Minnetyan, Levon↗
NASA NTRS1997

Evaluation of a Progressive Failure Analysis Methodology for Laminated Composite Structures

A progressive failure analysis methodology has been developed for predicting the nonlinear response and failure of laminated composite structures. The progressive failure analysis uses C plate and shell elements based on classical lamination theory to calculate the in-plane stresses. Several failure criteria, including the maximum strain criterion, Hashin's criterion, and Christensen's criterion, are used to predict the failure mechanisms. The progressive failure analysis model is implemented into a general purpose finite element code and can predict the damage and response of laminated composite structures from initial loading to final failure.

Sleight, David W.↗
NASA NTRS2004

A Comparison of Weld-Repaired and Base Metal for Inconel 718 and CRES 321 at Cryogenic and Room Temperatures

Fatigue crack growth tests were conducted to characterize the performance of Inconel 718 and CRES 321 welds, weld heat-affect-zone and parent metal at room temperature laboratory air and liquid nitrogen (-196oC) environments. The results of this study were required to predict the damage tolerance behavior of proposed orbiter main engine hydrogen fuel liner weld repairs. Experimental results show that the room and cryogenic temperature fatigue crack growth characteristics of both alloys are not significantly degraded by the weld repair process. However, both Inconel 718 and CRES 321 exhibited lower apparent toughness within the weld repair region compared to the parent metal.

Newman, John A.↗
NASA NTRS2008

A Novel Multiscale Physics Based Progressive Failure Methodology for Laminated Composite Structures

A variable fidelity, multiscale, physics based finite element procedure for predicting progressive damage and failure of laminated continuous fiber reinforced composites is introduced. At every integration point in a finite element model, progressive damage is accounted for at the lamina-level using thermodynamically based Schapery Theory. Separate failure criteria are applied at either the global-scale or the microscale in two different FEM models. A micromechanics model, the Generalized Method of Cells, is used to evaluate failure criteria at the micro-level. The stress-strain behavior and observed failure mechanisms are compared with experimental results for both models.

Pineda, Evan J.↗
NASA NTRS2011

Into the Eye

NASA's aeronautical research not only encompasses advancing aircraft technology and aviation safety for today and the future, but it also has a branch that deals with Airborne Science. This Airborne Science branch possesses unique airborne flight vehicles (manned and unmanned) whose sole purpose is to take scientists and their experiments anywhere in the world, into nearly any climatic condition, to gather the data they need for their research. This research spans such fields as; global warming, weather analysis, air and water pollution, mineral and archaeology search, earthquake damage and prediction, and yes, hurricanes. The data we obtain will hopefully, one day, allow us to better understand our planet, its natural forces and man's interaction with them.

Ewers, Richard G.↗
NASA NTRS2017

Re-Tooling the Agency's Engineering Predictive Practices for Durability and Damage Tolerance

Over the past decade, the Agency has placed less emphasis on testing and has increasingly relied on computational methods to assess durability and damage tolerance (D&DT) behavior when evaluating design margins for fracture-critical components. With increased emphasis on computational D&DT methods as the standard practice, it is paramount that capabilities of these methods are understood, the methods are used within their technical limits, and validation by well-designed tests confirms understanding. The D&DT performance of a component is highly dependent on parameters in the neighborhood of the damage. This report discusses D&DT method vulnerabilities.

Piascik, Robert S.↗
NASA NTRS2020

Tensile Creep Behavior of SiC(f)/SiC Ceramic Matrix Minicomposites

Single fiber-tow minicomposites represent the major load-bearing element of woven and laminate ceramic matrix composites (CMCs). To understand the effects of fiber type, fiber content, and matrix cracking on tensile creep in SiCf/SiC CMCs, single-tow SiCf/SiC minicomposites with different fiber types and contents were investigated. The minicomposites studied contained either Hi-Nicalon™ or Hi-Nicalon™ Type S SiC fibers with a boron nitride (BN) interphase and a chemical-vapor-infiltrated-silicon-carbide (CVI-SiC) matrix. Tensile creep was performed at 1200 °C in air. A bottom-up creep modeling approach was applied where creep parameters of the fibers and matrix were obtained separately at 1200 °C. Next, a theoretical model based on the rule of mixtures was derived to model the fiber and matrix creep-time-dependent stress redistribution. Fiber and matrix creep parameters, load transfer model results, and numerical modeling were used to construct a creep strain model to predict creep damage evolution of minicomposites with different fiber types and contents.

SiC/SiC Minicomposites Creep↗
NASA NTRSDate not supplied

A Convolutional Neural Network for Multiscale Modeling of Composite Materials

An artificial convolutional neural network was created to efficiently mimic a micromechanics model, the High Fidelity Generalized Method of Cells, for use in multi-scale structural finite element analysis. The network was found to quickly and accurately replicate the stiffness predicted by the micromechanics model using a 2D image of an idealized representative volume element of a fiber/matrix microstructure. The long-term goal of this work is to efficiently apply multi-scale methods for predicting the damage progression of a composite structure.

Composites↗