Search NASA⌕ Search

SEARCH · Search NASA

Results for “IMPACT STRENGTH”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Atomic Data and Spectral Line Intensities for Ne III

Electron impact collision strengths, energy levels, oscillator strengths and spontaneous radiative decay rates are calculated for Ne III. The configurations used are 2s(sup 2) 2p(sup 4),2s2p(sup 5),2s(sup 2) 2p(sup 3)3s, and 2s(sup 2)3p(sup 3)3d giving rise to 57 fine-structure levels in intermediate coupling. Collision strengths are calculated at five incident energies, 5, 10, 15, 20, and 25 Ry. Excitation rate coefficients are calculated by assuming a Maxwellian electron velocity distribution at an electron temperature of logT,(K)=5.0, corresponding to maximum abundance of Ne III. Using the excitation rate coefficients and the radiative transition rates, statistical equilibrium equations for level populations are solved at electron densities covering the range of 10(exp 8)-10(exp 14) per cubic centimeter. Relative spectral line intensities are calculated. Proton excitation rates between the lowest three levels have been included in the statistical equilibrium equations. The predicted Ne III line intensities are compared with SERTS rocket measurements of a solar active region and of a laboratory EUV light source.

Bhatia, A. K.↗
NASA NTRS2003

Atomic Data and Spectral Line Intensities for S XI

Electron impact collision strengths, energy levels, oscillator strengths and spontaneous radiative decay rates are calculated for S XI. The configurations included are 2s(sup 2)2psup 2), 2s2p(sup 3), 2p(sup 4), 2s(sup 2)2p3l and 2s(sup 2)2p4l (I = s , p , d) giving rise to 72 fine-structure levels in intermediate coupling. Collision strengths are calculated at five incident energies, 32, 60, 90, 120, and 150 Ry. Excitation rate coefficients are calculated as a function of electron temperature by assuming a Maxwellian electron velocity distribution. Using the excitation rate coefficients and the radiative transition rates, statistical equilibrium equations for level populations are solved: The effects of resonances, proton rates, photoexcitation and cascades on level populations have been investigate. The predicted S XI line intensities are compared with EUV and UV observations of the quiet and active Sun.

Landi, E.↗
NASA NTRS2004

Atomic Data and Spectral Line Intensities for Ne III

Electron impact collision strengths, energy levels, oscillator strengths, and spontaneous radiative decay rates are calculated for Ne III. The configurations used are 2s(sup 2)2p(sup 4), 2s2p(sup 5), 2p(sup 6), 2s(sup 2)2p(sup 3)3(sub s), 2s(sup 2)2p(sup 3)3p, and 2s(sup 2)2p(sup 3)3d giving rise to 86 fine-structure levels in intermediate coupling. Collision strengths are calculated at five incident energies, 5.2, 10, 15, 20 and 25 Ry. Excitation rate coefficients are calculated as a function of electron temperature by assuming a Maxwellian electron velocity distribution. Using the excitation rate coefficients and the radiative transition rates, statistical equilibrium equations for level populations are solved at electron densities covering the range of 10(exp 8) - 10(exp 14)/cc at an electron temperature of logTe/K = 5.0, corresponding to maximum abundance of Ne III. Relative spectral line intensities are calculated.

Landi, E.↗
NASA NTRS1990

Stress Dependence of Ultrasonic Velocity in Unidirectional Graphite/Epoxy Composites for Longitudinal Waves Propagating Along the Direction of Stress

The first measurements of the stress induced velocity changes for propagation directions along the direction of applied stress in gr/ep composites have been presented. For propagation and stress direction perpendicular to the fiber direction, the data demonstrated a linear relation between normalized velocity shift and stress. After corrections for the delay line were made, the slope or SAC was determined and compared favorably with the expected value calculated from the previously determined nonlinear coefficients of this material. The ratio of the SAC to the elastic compliance for this direction of loading was evaluated and found to have a value similar to numerous other materials which have very different linear elastic properties. Measurements with stress and propagation along the fibers yielded unusual behavior. The curves were very nonlinear and even shifted direction at higher loads. The large scatter in the data due to bond variations made separation of material effects from bond induced artifacts impossible. Thus the SAC, R, and the remaining two unknown TOEC's could not be determined for this direction of propagation. These measurements further expand the basis of determining nonlinear elastic properties of composite materials. These properties may be useful in developing much needed NDE techniques to determine such important parameters as residual stress after cure and residual strength after impact damage. Additional study is needed to measure the nonlinear behavior in other composite materials including angle ply laminates. Also, other techniques to measure elastic nonlinearity such as harmonic generation should be applied to composites to improve the understanding of these properties and their importance.

Prosser, William H.↗
NASA NTRS2004

Atomic Data and Spectral Line Intensities for Ar XII

Electron impact collision strengths; energy levels; oscillator strengths and spontaneous radiative decay rates are calculated for Ar XII. The configurations used are 2s(exp 2)2p(exp 3), 2s2p(exp4), 2p(exp 5), 2s22p23s, 2s(exp 2)2p(exp 2)3p, and 2s(exp 2)2p(exp 2)3d giving rise to 72 fine-structure levels in intermediate coupling. Collision strengths are calculated at five incident energies: 35,70, 105, 140 and 175 Ry. They are complemented by Coulomb-Born limits towards infinite collision energy for forbidden transitions and line strengths for optically allowed transitions. Excitation rate coefficients are calculated as a function of electron temperature by assuming a Maxwellian electron velocity distribution. Using the excitation rate coefficients and the radiative transition rates, statistical equilibrium equations for level populations are solved at electron densities covering the range of 10(exp 8)-101(exp 14) cm(exp -3) at an electron temperature of log T(sub e)/K = 6.4, corresponding to maximum abundance of Ar XII. Relative spectral line intensities are calculated.

Eissner, W.↗
NASA NTRS2004

Atomic Data and Spectral Line Intensities for Ar XII

Electron impact collision strengths, energy levels, oscillator strengths and spontaneous radiative decay rates are calculated for Ar XII. The configurations used are 2s(sup 2)p(sup 3), 2s(sup 2)p(sup 4), 2p(sup 5), 2s(sup 2)2p(sup 2)3s, 2s(sup 2)2p(sup 2)3p, and 2s(sup 2)2p(sup 2)3d giving rise to 72 fine-structure levels in intermediate coupling. Collision strengths are calculated at five incident energies: 35, 70, 105, 140 and 175 Ry. They are complemented by Coulomb-Born limits towards infinite collision energy for forbidden transitions and line strengths for optically allowed transitions. Excitation rate coefficients are calculated as a function of electron temperature by assuming a Maxwellian electron velocity distribution. Using the excitation rate coefficients and the radiative transition rates, statistical equilibrium equations for level populations are solved at electron densities covering the range of 10(exp 8)-10(exp 14)/cm(exp 3) at an electron temperature of log T(sub e)/K = 6.4, corresponding to maximum abundance of AR-XII. Relative spectral line intensities are calculated.

Eissner, W.↗
NASA NTRS2007

Atomic Data and Spectral Line Intensities for CA XVII

Electron impact collision strengths, energy levels, oscillator strengths and spontaneous radiative decay rates are calculated for Ca XVII. The configurations used are 2s(sup 2), 2s2p, 2p(sup 2), 2l3l', 214l' and 2s5l', with l = s,p and l' = s,p, d giving rise to 92 fine-structure levels in intermediate coupling. Collision strengths are calculated at seven incident energies (15, 30, 75, 112.5, 150, 187.5 and 225 Ry) for the transitions within the three lowest configurations corresponding to the 10 lowest energy levels, and five incident energies (75, 112.5, 150, 187.5 and 225 Ry) for transitions between the lowest five levels and the n = 3,4,5 configurations. Calculations have been carried out using the distorted wave approximation. Excitation rate coefficients are calculated as a function of electron temperature by assuming a Maxwellian electron velocity distribution. Using the excitation rate coefficients and the radiative transition rates of the present work, and R-Matrix results for the 2s2, 2s2p, 2p2 configurations available in the literature, statistical equilibrium equations for level populations are solved at electron densities covering the range of 10(exp 8)-10(exp 14)/cu cm at an electron temperature of log Te(K)=6.7, corresponding to the maximum abundance of Ca XVII. Spectral line intensities are calculated, and their diagnostic relevance L; discussed. This dataset will be made available in the next version of the CHIANTI database.

Bhatia, A.K.↗
NASA NTRS2010

Simplification of Fatigue Test Requirements for Damage Tolerance of Composite Interstage Launch Vehicle Hardware

The issue of fatigue loading of structures composed of composite materials is considered in a requirements document that is currently in place for manned launch vehicles. By taking into account the short life of these parts, coupled with design considerations, it is demonstrated that the necessary coupon level fatigue data collapse to a static case. Data from a literature review of past studies that examined compressive fatigue loading after impact and data generated from this experimental study are presented to support this finding. Damage growth, in the form of infrared thermography, was difficult to detect due to rapid degradation of compressive properties once damage growth initiated. Unrealistically high fatigue amplitudes were needed to fail 5 of 15 specimens before 10,000 cycles were reached. Since a typical vehicle structure, such as the Ares I interstage, only experiences a few cycles near limit load, it is concluded that static compression after impact (CAI) strength data will suffice for most launch vehicle structures.

Nettles, A. T.↗
NASA NTRS2010

Atomic Data and Spectral Line Intensities for Ni XI

Electron impact collision strengths, energy levels, oscillator strengths and spontaneous radiative decay rates are calculated for Ni XI. We include in the calculations the 10 lowest configurations, corresponding to 164 fine structure levels: 3s(sup 2)3p(sup 6), 3s(sup 2)3p(sup 5)3d, 3s(sup 2)3p(sup 4)3d(sup 2), 3s3p(sup 6)3d, 3s(sup 2)3p(sup 5)4l and 3s3p6 4l with l =.s, p, d. Collision strengths are calculated at five incident energies for all transitions: 7.1, 16.8, 30.2, 48.7 and 74.1 Ry above the threshold of each transition. An additional energy, very close to the transition threshold, has been added, whose value is between 0.06 Ry and 0.25 Ry depending on the lower level. Calculations have been carried out using the Flexible Atomic Code and the distorted wave approximation. Excitation rate coefficients are calculated as a function of electron temperature by assuming a Maxwellian electron velocity distribution. Using the excitation rate coefficients and the radiative transition rates of the present work, combined with Close Coupling collision excitation rate coefficient available in the literature for the lowest 17 levels, statistical equilibrium equations for level populations are solved at electron densities covering the 10(exp 8)-10(exp 14) cu cm range and at an electron temperature of logT(sub c)(K)=6.1, corresponding to the maximum abundance of Ni XI. Spectral line intensities are calculated, and their diagnostic relevance is discussed. This dataset will be made available in the next version of the CHIANTI database.

Bhatia, A. K.↗
NASA NTRS2011

Atomic Data and Spectral Line Intensities for NI XVII

Electron impact collision strengths, energy levels, oscillator strengths, and spontaneous radiative decay rates are calculated for Ni XVII. We include in the calculations the 23 lowest configurations, corresponding to 159 fine-structure levels: 3l3l', 3l4l0'' , and 3s5l0''' , with l,l' = s,p,d, l'' = s,p,d, f, and l''' = s,p,d. Collision strengths are calculated at five incident energies for all transitions at varying energies above the threshold of each transition. One additional energy, very close to the threshold of each transition, has also been included. Calculations have been carried out using the Flexible Atomic Code in the distorted wave approximation. Additional calculations have been performed with the University College London suite of codes for comparison. Excitation rate coefficients are calculated as a function of electron temperature by assuming a Maxwellian electron velocity distribution. Using the excitation rate coefficients and the radiative transition rates of the present work, statistical equilibrium equations for level populations are solved at electron densities covering the range of 10(exp 8) - 10(exp 14) / cubic cm and at an electron temperature of logT(sub e)e(K) = 6.5, corresponding to the maximum abundance of Ni XVII. Spectral line intensities are calculated, and their diagnostic relevance is discussed. This dataset will be made available in the next version of the CHIANTI database

Bhatia, A. K.↗
NASA NTRS2012

Atomic Data and Spectral Line Intensities for Ca IX

Electron impact collision strengths, energy levels, oscillator strengths and spontaneous radiative decay rates are calculated for Ca IX. We include in the calculations the 33 lowest configurations in the n = 3, 4, 5 complexes, corresponding to 283 fine structure levels in the 3l3l ', 3l4l'' and 3l4l''' configurations, where l,l' = s, p, d, l '' = s, p, d, f and l''' = s, p, d, f, g. Collision strengths are calculated at five incident energies for all transitions: 5.8, 13.6, 24.2, 38.6 and 57.9 Ry above the threshold of each transition. An additional energy, very close to the transition threshold, has been added, whose value is between 0.0055 Ry and 0.23 Ry depending on the levels involved. Calculations have been carried out using the Flexible Atomic Code and the distorted wave approximation. Excitation rate coefficients are calculated as a function of electron temperature by assuming a Maxwellian electron velocity distribution. Using the excitation rate coefficients and the radiative transition rates calculated in the present work, statistical equilibrium equations for level populations are solved at electron densities covering the 10(exp 8)-10(exp 14)/cubic cm range and at an electron temperature of log T(sub e)(K)=5.8, corresponding to the maximum abundance of Ca IX. Spectral line intensities are calculated, and their diagnostic relevance is discussed.

Landi, E.↗
NASA NTRS2011

Atomic Data and Spectral Line Intensities for Ni XV

Electron impact collision strengths, energy levels, oscillator strengths, and spontaneous radiative decay rates are calculated for Ni XV.Weinclude in the calculations the 9 lowest configurations, corresponding to 126 fine structure levels: 3s23p2, 3s3p3, 3s23p3d, 3p4, 3s3p23d, and 3s2 3p4l with l =, s, p, d, f. Collision strengths are calculated at five incident energies for all transitions: 7.8, 18.5, 33.5, 53.5, and 80.2 Ry above the threshold of each transition. An additional energy, very close to the transition threshold, has been added, whose value is between 0.004 and 0.28 Ry depending on the levels involved. Calculations have been carried out using the Flexible Atomic Code and the distorted-wave approximation. Excitation rate coefficients are calculated as a function of electron temperature by assuming a Maxwellian electron velocity distribution. Using the excitation rate coefficients and the radiative transition rates calculated in the present work, statistical equilibrium equations for level populations are solved at electron densities covering the 10(exp 8)-10(exp 14)/cu cm range and at an electron temperature of log T(sub e)(K) = 6.4, corresponding to the maximum abundance of Ni XV. Spectral line intensities are calculated, and their diagnostic relevance is discussed. This dataset will be made available in the next version of the CHIANTI database.

Landi, E.↗
NASA NTRS2013

Stochastic Nonlinear Response of Woven CMCs

It is well known that failure of a material is a locally driven event. In the case of ceramic matrix composites (CMCs), significant variations in the microstructure of the composite exist and their significance on both deformation and life response need to be assessed. Examples of these variations include changes in the fiber tow shape, tow shifting/nesting and voids within and between tows. In the present work, the influence of scale specific architectural features of woven ceramic composite are examined stochastically at both the macroscale (woven repeating unit cell (RUC)) and structural scale (idealized using multiple RUCs). The recently developed MultiScale Generalized Method of Cells methodology is used to determine the overall deformation response, proportional elastic limit (first matrix cracking), and failure under tensile loading conditions and associated probability distribution functions. Prior results showed that the most critical architectural parameter to account for is weave void shape and content with other parameters being less in severity. Current results show that statistically only the post-elastic limit region (secondary hardening modulus and ultimate tensile strength) is impacted by local uncertainties both at the macro and structural level.

Kuang, C. Liu↗
NASA NTRS2022

Comparison of U.S. and Russian Slow Crack Growth Data and Models

Both the US and Russian space programs use similar predictive models for design of fused silica windows on the International space station. The Russian model can be derived from the power expression for slow crack growth (SCG) or “static fatigue.” The US uses both power and exponential models. Despite the similarity of models and data fitting approach (linear regression and right censoring), different SCG parameters have been derived by US and Russian parties for the same material (Russian fused silica) tested in a similar manner. The difference appears to be related to the use of short-term strength data along with the longer-term static fatigue data, with the power law parameter n being very sensitive to the conversion of strength data into equivalent static data. This hybrid approach is feasible if strength data is measured with a constant stress rate and is appropriately converted to a static equivalent. More research into the approach is needed. However, because of the nonlinear behavior of fused silica in log(v) – log(K(I) ) space and the sensitivity of parameter estimation to fit range, the exponential model is a better choice regardless of test method. Functions are given to convert parameters from the Russian model to those in the US model. However, accurate conversion is hampered by the lack of inert strength data. When the same test technique is used, US and Russian materials exhibit very similar parameters.

Silica, strength, impact, crack growth, windows, I↗
NASA NTRS2023

Damage Tolerance Comparison of IM7/8552 and T1100/3960 Carbon Fiber/Epoxy Sandwich Structure in Support of the Space Launch System Payload Adapter Fitting

As technology evolves and improves within the science of composite materials, new fiber/ resin systems are being developed for improved properties given certain loading and environmental scenarios. Improving the room temperature damage tolerance capabilities has long been one of the goals in the carbon fiber/polymer composite industry. Recently a new fiber/epoxy system has been introduced that is claimed to have superior damage tolerance capabilities. To examine if this new carbon fiber/epoxy composite material would be of benefit to a program to manufacture a Payload Adapter Fitting (PAF) for NASA’s Space Launch System (SLS) rocket, the question was asked as to just how much damage tolerance could be realized if this new system were used. Compression after impact (CAI) strength of sandwich structure is one of the leading metrics being used to evaluate materials for the PAF program. As a result, a comparison of this new fiber/resin system with a very common (and planned baseline) fiber/resin system with respect to CAI was considered in this study. While it was already known that the older, baseline carbon fiber structure would not have as good damage tolerance characteristics as the newer carbon fiber system, the quantitative difference in damage tolerance was sought in this study since no other CAI data could be found in open literature on sandwich structures made with this new fiber/resin system.

A.T. Nettles↗
DOE OSTI2022

Emergence of a nocturnal low-level jet from a broad baroclinic zone

An analytical model is presented for the generation of a Blackadar-like nocturnal low-level jet in a broad baroclinic zone. The flow is forced from below (flat ground) by a surface buoyancy gradient and from above (free atmosphere) by a constant pressure gradient force. Diurnally-varying mixing coefficients are specified to increase abruptly at sunrise and decrease abruptly at sunset. With attention restricted to a surface buoyancy that varies linearly with a horizontal coordinate, the Boussinesq-approximated equations of motion, thermal energy, and mass conservation reduce to a system of one-dimensional equations that can be solved analytically. Sensitivity tests with southerly jets suggest that (i) stronger jets are associated with larger decreases of the eddy viscosity at sunset (as in Blackadar theory), (ii) the nighttime surface buoyancy gradient has little impact on jet strength, and (iii) for pure baroclinic forcing (no free-atmosphere geostrophic wind), the nighttime eddy diffusivity has little impact on jet strength, but the daytime eddy diffusivity is very important and has a larger impact than the daytime eddy viscosity. The model was applied to a jet that developed in fair weather conditions over the Great Plains from southern Texas to northern South Dakota on 1 May 2020. The ECMWF Reanalysis v5 (ERA5) for the afternoon prior to jet formation showed that a broad north-south-oriented baroclinic zone covered much of the region. The peak model-predicted winds were in good agreement with ERA5 winds and lidar data from the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) central facility in north-central Oklahoma.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1987

A nondestructive technique for predicting the strength remaining in filament wound composites subjected to low-level impact

A model for predicting the fracture strength of homogeneous materials is proposed. Impacted FWC samples were evaluated using ultrasonic testing and an X-ray dye penetration method. The ability of the model to measure fracture strength was also examined. The relation between attenuation and velocity measurements is studied. It is observed that the X-ray method is not useful for predicting fracture strength because the dye could not penetrate the matrix. It is noted that fracture strength predictions derived from the fracture mechanical model and the ultrasonic measurements correlate well with actual measured fracture strengths.

Madaras, E. I.↗