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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

Pulse Compression Techniques for Laser Generated Ultrasound

Laser generated ultrasound for nondestructive evaluation has an optical power density limit due to rapid high heating that causes material damage. This damage threshold limits the generated ultrasound amplitude, which impacts nondestructive evaluation inspection capability. To increase ultrasound signal levels and improve the ultrasound signal-to-noise ratio without exceeding laser power limitations, it is possible to use pulse compression techniques. The approach illustrated here uses a 150mW laser-diode modulated with a pseudo-random sequence and signal correlation. Results demonstrate the successful generation of ultrasonic bulk waves in aluminum and graphite-epoxy composite materials using a modulated low-power laser diode and illustrate ultrasound bandwidth control.

Anastasi, R. F.↗
NASA NTRS2004

Pseudo-Random Modulation of a Laser Diode for Generating Ultrasonic Longitudinal Waves

Laser generated ultrasound systems have historically been more complicated and expensive than conventional piezoelectric based systems, and this fact has relegated the acceptance of laser based systems to niche applications for which piezoelectric based systems are less suitable. Lowering system costs, while improving throughput, increasing ultrasound signal levels, and improving signal-to-noise are goals which will help increase the general acceptance of laser based ultrasound. One current limitation with conventional laser generated ultrasound is a material s damage threshold limit. Increasing the optical power to generate more signal eventually damages the material being tested due to rapid, high heating. Generation limitations for laser based ultrasound suggests the use of pulse modulation techniques as an alternate generation method. Pulse modulation techniques can spread the laser energy over time or space, thus reducing laser power densities and minimizing damage. Previous experiments by various organizations using spatial or temporal pulse modulation have been shown to generate detectable surface, plate, and bulk ultrasonic waves with narrow frequency bandwidths . Using narrow frequency bandwidths improved signal detectability, but required the use of expensive and powerful lasers and opto-electronic systems. The use of a laser diode to generate ultrasound is attractive because of its low cost, small size, light weight, simple optics and modulation capability. The use of pulse compression techniques should allow certain types of laser diodes to produce usable ultrasonic signals. The method also does not need to be limited to narrow frequency bandwidths. The method demonstrated here uses a low power laser diode (approximately 150 mW) that is modulated by controlling the diode s drive current and the resulting signal is recovered by cross correlation. A potential application for this system which is briefly demonstrated is in detecting signals in thick composite materials where attenuation is high and signal amplitude and bandwidth are at a premium.

Madaras, Eric I.↗
NASA NTRS2024

Analytical Simulation of Effects of Local Mechanisms and Microstructure on Creep Response of Unidirectional Ceramic Matrix Composites

A micromechanics-based method has been developed to analyze the creep response of uncoated ceramic matrix minicomposites. Although the global stress level at which the creep response is analyzed is lower than the composite proportional limit, local stresses are assumed to be high enough that localized damage is present in the composite in the form of matrix microcracks. To model the composite creep response, including the effects of matrix cracking, a fiber shear lag-based methodology is employed. In this approach, stresses are assumed to vary in the fiber as a function of time and distance from the crack plane. The varying stresses are then used to compute the overall creep strain for the composite. Various assumptions regarding the level of matrix microcracking in the composite and the level of creep in the fiber and matrix in various portions of the composite unit cell are also examined. The creep response of the fiber is modeled using a linear Burgers model. The model is applied to a SiCf/SiC unidirectional minicomposite system. The computed creep results are compared to experimentally obtained values. The effects of the local fiber volume fraction on the overall creep response of the composite are also studied. This work will allow increased understanding of the key material damage mechanisms and load sharing that take place during creep conditions and can be expanded to provide improved analysis methods for full macrocomposites.

Micromechanics↗
NASA NTRS2024

Analytical Simulation of the Effects of Local Mechanisms and Microstructure on the Creep Response of Unidirectional Ceramic Matrix Composites

A micromechanics-based method has been developed to analyze the creep response of uncoated ceramic matrix minicomposites. Although the global stress level at which the creep response is analyzed is lower than the composite proportional limit, local stresses are assumed to be high enough that localized damage is present in the composite in the form of matrix microcracks. To model the composite creep response including the effects of matrix cracking, a fiber shear lag-based methodology is employed. In this approach, stresses are assumed to vary in the fiber as a function of time and distance from the crack plane. The varying stresses are then used to compute the overall creep strain for the composite. Various assumptions regarding the level of matrix microcracking in the composite, and the level of creep in the fiber and matrix in various portions of the composite unit cell, are also examined. The creep response of the fiber is modeled using a linear Burgers model. The model is applied to a SiC f /SiC unidirectional minicomposite system. The computed creep results are compared to experimentally obtained values. The effects of the local fiber volume fraction on the overall creep response of the composite are also studied. This work will allow increased understanding of the key material damage mechanisms and load sharing that take place during creep conditions and can be expanded to provide improved analysis methods for full macrocomposites.

Micromechanics↗
DOE OSTI2024

Design, Fabrication and Testing of Surveillance Test Articles for MSR Materials Degradation Management

This report details the design, fabrication, and testing of surveillance test articles aimed at assessing material damage in reactor-relevant environments for effective degradation management. Two types of surveillance test articles with reduced sizes were developed based on design algorithms and finite element modeling: welded design and interlocking design. A furnace heating setup was adopted to apply multiple thermal cyclic loading profiles on the test articles with a temperature range of 500°C - 700°C, while the strain response was monitored using a digital image correlation technique. The testing results demonstrated the successful capturing of expected strain range for welded design while machining tolerance should be improved to engage strain coupling in the interlocking design. Mid-term (500 hours) and long-term (1500 hours) cyclic tests were conducted on welded test articles. A constant strain range of ~0.6% was observed at the specimen with testing under 500 hours, while a gradual decrease of strain at specimen was observed after 500 hours. Non-destructive evaluation through X-ray computed tomography confirmed the microcracks in the welds at specimen-driver joints after cyclic test that caused the strain change. Creep testing of the specimen after long-term cyclic test revealed a short creep life than expected. A multi-profile cyclic test was also conducted on a test article and demonstrated consistent strain response under different temperature ramp rates. The report also briefly discussed the challenges and future research efforts to advance test article development for material surveillance.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2025

Multimodal azimuthal oscillations in electron beam generated E×B plasma

Electron beam (e-beam) generated plasmas with applied crossed electric and magnetic (E×B) fields are promising for low-damage material processing. However, these plasmas can be subject to the formation of azimuthally propagating structures that enhance the radial transport of energetic charged species, which can harm the gentle processing capability of the plasma. In this work, we investigate the azimuthal structure formation in an e-beam generated E×B plasma using experimental diagnostics and 2D3V particle-in-cell simulations. Our findings demonstrate the formation of multiple simultaneously occurring azimuthally propagating modes that exhibit nontrivial radial dependence. It is suggested that the multimodal azimuthal spectrum is caused in part by the radial outflow of ions in the plasma.

electron beams↗
DOE OSTI2025

Sound Speeds of Solids from Ultrasonic Pulse Receiver Measurements

A common method of determining elastic material properties is utilizing an ultrasonic pulse receiver. This is a non-destructive test (NDT) causing no plastic deformation of the material. It requires a pulse generator, oscilloscope, and two transducers to measure the sound velocity of a material. Both longitudinal and shear sound velocities may be obtained by utilizing the appropriate transducer. Acoustic nondestructive testing methods are often used in manufacturing certification processes and for material defect detection in industry. These methods can also be utilized to directly measure the elastic moduli of a material without damaging the material. Overall, it is a low-cost experiment with minimal preparation, and is easy to use.

36 MATERIALS SCIENCE↗
NASA NTRS1973

Self-sterilizing polymers

Addition of approximately 1% paraformaldehyde to room-temperature-vulcanizing potting polymer results in effective, controllable germicide. When heated above ambient temperatures, paraformaldehyde releases dry formaldehyde, which can penetrate enclosed areas and packages, will not damage material, and leaves no permanent residue.

Tulis, J. J.↗
NASA NTRS1975

Solar-wind and solar-flare maturation of the lunar regolith

Detailed predictions concerning the depth and time-dependent accumulation of solar-wind effects and solar-flare tracks in lunar dust grains were obtained by use of an adaptation of a Monte Carlo soil-mixing computer code described by Duraud et al. (1975). The predictions are compared to experimental measurements obtained by analyzing lunar dust grains as well as artificially irradiated minerals by a variety of techniques. A study of amorphous coatings of solar-wind radiation-damaged material on certain lunar grains sets limits on the integrated residence time of these grains in the ancient solar wind. Other topics discussed include solar wind maturation, the peculiar shape of the experimental distribution of central track densities in 50-micron grains, and the interpretation of both track gradients in 50-micron feldspars and the relatively 'low' concentration of solar-wind species implanted in ilmenite grains.

Bibring, J. P.↗
NASA NTRS1980

Degradation of tensile and shear properties of composites exposed to fire or high temperature

The decrease in ultimate tensile strength, shear strength, tensile modulus, and shear modulus of fiber reinforced composites exposed to fire or to high temperature was investigated. A simple model was developed for calculating the mass loss of the material and the thickness of the char layer. The mass loss as well as the degradation in tensile and shear properties of Fiberite T300/1034 and Hercules AS/3501-6 graphite epoxy composites exposed to fire were measured. A correlation between the degradation in properties and the calculated mass loss and the char layer thickness was developed. A technique was proposed for predicting material damage through the use of such correlations.

Pering, G. A.↗
NASA NTRS1986

Noncontacting Measurement With a Thermocouple

Tentlike covering brings thermocouple to within few degrees of surface temperature. Technique originally developed for measuring surface temperature of quartz fabric under radiant heating requires no direct contact with heated surface. Technique particularly useful when measuring surface temperatures of materials damaged if thermocouple or other temperature sensor attached.

Weatherill, W. T.↗
NASA NTRS1987

Buckling tests of a 10 foot diameter stiffened cylinder with rectangular cutouts

A 10-foot diameter aluminum cylinder with rectangular cutouts in its ring and stringer stiffened wall was loaded to failure by an end bending moment. A 24x27 inch cutout, centered on the compression side of the shell, was first cut into the cylinder. After testing, the cutout area was enlarged to a 36/36 inch square cutout that removed the material damaged by buckling during the first test. After the second buckling test, the cutout area was patched with an equivalent stiffness plate bolted over the cutout hole. The cylinder was rotated 120 deg. and a 18x18 inch square hole cut into the center of the new compression side of the shell. Test specimen details, test procedures, and test results are presented.

Davis, Randall C.↗
NASA NTRS1991

Computational methods for structural load and resistance modeling

An automated capability for computing structural reliability considering uncertainties in both load and resistance variables is presented. The computations are carried out using an automated Advanced Mean Value iteration algorithm (AMV +) with performance functions involving load and resistance variables obtained by both explicit and implicit methods. A complete description of the procedures used is given as well as several illustrative examples, verified by Monte Carlo Analysis. In particular, the computational methods described in the paper are shown to be quite accurate and efficient for a material nonlinear structure considering material damage as a function of several primitive random variables. The results show clearly the effectiveness of the algorithms for computing the reliability of large-scale structural systems with a maximum number of resolutions.

Thacker, B. H.↗
NASA NTRS1991

Detailed analysis and test correlation of a stiffened composite wing panel

Nonlinear finite element analysis techniques are evaluated by applying them to a realistic aircraft structural component. A wing panel from the V-22 tiltrotor aircraft is chosen because it is a typical modern aircraft structural component for which there is experimental data for comparison of results. From blueprints and drawings supplied by the Bell Helicopter Textron Corporation, a very detailed finite element model containing 2284 9-node Assumed Natural-Coordinate Strain (ANS) elements was generated. A novel solution strategy which accounts for geometric nonlinearity through the use of corotating element reference frames and nonlinear strain displacements relations is used to analyze this detailed model. Results from linear analyses using the same finite element model are presented in order to illustrate the advantages and costs of the nonlinear analysis as compared with the more traditional linear analysis. Strain predictions from both the linear and nonlinear stress analyses are shown to compare well with experimental data up through the Design Ultimate Load (DUL) of the panel. However, due to the extreme nonlinear response of the panel, the linear analysis was not accurate at loads above the DUL. The nonlinear analysis more accurately predicted the strain at high values of applied load, and even predicted complicated nonlinear response characteristics, such as load reversals, at the observed failure load of the test panel. In order to understand the failure mechanism of the panel, buckling and first ply failure analyses were performed. The buckling load was 17 percent above the observed failure load while first ply failure analyses indicated significant material damage at and below the observed failure load.

Davis, D. Dale, Jr.↗
NASA NTRS1993

Modeling of failure and response to laminated composites subjected to in-plane loads

An analytical model was developed for predicting the response of laminated composites with or without a cutout and subjected to in-plane tensile and shear loads. Material damage resulting from the loads in terms of matrix cracking, fiber-matrix shearing, and fiber breakage was considered in the model. Delamination, an out-of-plane failure mode, was excluded from the model.

Shahid, Iqbal↗
NASA NTRS1998

Collapse of Composite Cylinders in Bending

This paper summarizes the results of a numerical and experimental study of the collapse behavior of small-scale graphite-epoxy cylindrical shells subjected to overall bending loads, and in one case, an initial internal pressure. Shells with quasi-isotropic and orthotropic inplane stiffness properties are studied. Numerical results from geometrically nonlinear finite element analyses and results from experiments using a specially-built apparatus indicate that extensive stable postbuckling responses occur. Orthotropy influences the buckling values and the extent to which the bending moment decreases after buckling. Material damage is observed to initiate in the vicinity of the nodal lines of the postbuckled deflection patterns. Numerical results indicate that the magnitudes of the shear stress resultants are greatest in these nodal regions. Failure of the internally pressurized cylinder is catastrophic.

Fuchs, Hannes P.↗
NASA NTRS2004

Research Performed within the Non-Destructive Evaluation Team at NASA Glenn Research Center

Non-destructive testing is essential in many fields of manufacturing and research in order to perform reliable examination of potentially damaged materials and parts without destroying the inherent structure of the materials. Thus, the Non-Destructive Evaluation (NDE) Team at NASA Glenn Research Center partakes in various projects to improve materials testing equipment as well as analyze materials, material defects, and material deficiencies. Due to the array of projects within the NDE Team at this time, five research aims were supplemental to some current projects. A literature survey of "DE and testing methodologies as related to rocks was performed. Also, Mars Expedition Rover technology was assessed to understand the requirements for instrumentation in harsh space environments (e.g. temperature). Potential instrumentation and technologies were also considered and documented. The literature survey provided background and potential sources for a proposal to acquire funding for ultrasonic instrumentation on board a future Mars expedition. The laboratory uses a Santec Systems AcousticScope AS200 acoustography system. Labview code was written within the current program in order to improve the current performance of the acoustography system. A sample of Reinforced Carbon/Carbon (RCC) material from the leading edge of the space shuttle underwent various non-destructive tests (guided wave scanning, thermography, computed tomography, real time x-ray, etc.) in order to characterize its structure and examine possible defects. Guided wave scan data of a ceramic matrix composite (CMC) panel was reanalyzed utilizing image correlations and signal processing variables. Additional guided wave scans and thermography were also performed on the CMC panel. These reevaluated data and images will be used in future presentations and publications. An additional axis for the guided wave scanner was designed, constructed, and implemented. This additional axis allowed incremental spacing of the previously fixed transducers for ultrasonic velocity measurements.

Burns, Erin A.↗
NASA NTRS2008

Numerically Modeling the Erosion of Lunar Soil by Rocket Exhaust Plumes

In preparation for the Apollo program, Leonard Roberts of the NASA Langley Research Center developed a remarkable analytical theory that predicts the blowing of lunar soil and dust beneath a rocket exhaust plume. Roberts assumed that the erosion rate was determined by the excess shear stress in the gas (the amount of shear stress greater than what causes grains to roll). The acceleration of particles to their final velocity in the gas consumes a portion of the shear stress. The erosion rate continues to increase until the excess shear stress is exactly consumed, thus determining the erosion rate. Roberts calculated the largest and smallest particles that could be eroded based on forces at the particle scale, but the erosion rate equation assumed that only one particle size existed in the soil. He assumed that particle ejection angles were determined entirely by the shape of the terrain, which acts like a ballistic ramp, with the particle aerodynamics being negligible. The predicted erosion rate and the upper limit of particle size appeared to be within an order of magnitude of small-scale terrestrial experiments but could not be tested more quantitatively at the time. The lower limit of particle size and the predictions of ejection angle were not tested. We observed in the Apollo landing videos that the ejection angles of particles streaming out from individual craters were time-varying and correlated to the Lunar Module thrust, thus implying that particle aerodynamics dominate. We modified Roberts theory in two ways. First, we used ad hoc the ejection angles measured in the Apollo landing videos, in lieu of developing a more sophisticated method. Second, we integrated Roberts equations over the lunar-particle size distribution and obtained a compact expression that could be implemented in a numerical code. We also added a material damage model that predicts the number and size of divots which the impinging particles will cause in hardware surrounding the landing rocket. Then, we performed a long-range ballistics analysis for the ejected particulates.

Source record↗