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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Investigation of the HPFTP first stage impeller crack

The occurrence of a crack in the HPFTP first stage impeller of pump 2608 R2 during test 750-245 prompted this analysis to examine possible causes of the failure. Preliminary analysis, using an existing NASTRAN model of the impeller, showed a deficiency in the model's ability to reliably calculate stress in the area of concern (outboard edge of the impeller shroud). A new NASTRAN model was constructed to better define the stress state in the area of crack initiations. Static stress analysis and normal models analysis were performed on the new model. Results are presented.

Source record↗
NASA NTRS1985

Design of stiffened composite panels with a fracture constraint

An automated procedure for designing minimum-weight composite panels subject to a local damage constraint under tensile loading was developed. A finite element program based on linear elastic fracture mechanics for calculating stress intensity factors (SIF) was incorporated in the design cycle. Panel fracture toughness was obtained by using a strain based criterion. A general purpose mathematical optimization algorithm was used for the weight minimization. Analytical sensitivity derivatives of the SIF employing the adjoint variable technique was used to enhance the computational efficiency of the procedure. Design results for both unstiffened and stiffened plates are presented.

Gurdal, Z.↗
NASA NTRS1985

Young thrust-fault scarps in the highlands - Evidence for an initially totally molten moon

Attention is given to thermoelastic stress calculations implying that if only the outer few hundreds of km of a moon with a cool interior were initially molten, the lunar highlands should not have young compressional tectonic features. Extrapolations from Apollo panoramic images showing young thrust faults in the highlands suggest that about 2000 thrust fault scarps exist on the highlands, generally occurring in series or complexes of four or five scarps that are on average 5 km long. The ages of the scarps range from 60 + or - 30 to 680 + or - 250 my, with a possible factor bias of +2 to -4. The scarps are the youngest endogenic features on the moon, and indicate that the moon was initially molten.

Binder, A. B.↗
NASA NTRS1985

Transport processes and ozone perturbations

Current understanding of stratospheric transport in the meridional plane is reviewed, and the implications of that conceptual framework for the ozone response to chlorofluorocarbon increases are considered. The possibility of seasonal and latitudinal variations in that response is stressed. Calculations of the changes in ozone that may have occurred between the period before widespread chlorofluorocarbon usage and the present day, and the changes that would be expected to occur at steady state for 1980 chlorofluorocarbon production levels, are presented. Finally, some of the uncertainties in the adopted transport framework and its applicability to the evaluation of future perturbations are explored.

Solomon, S.↗
NASA NTRS1986

Combined bearing and bypass loading on a graphite/epoxy laminate

A combined experimental and analytical study was conducted to determine the behavior of a graphite/epoxy laminate subjected to combined bearing and bypass loading. Single-fastener quasi-isotropic specimens were loaded at various bearing-bypass ratios until damage was produced at the fastener hole. Damage-onset strengths and damage modes were then analyzed using local hole-boundary stresses calculated by a finite-element analysis. The tension data showed the expected linear interaction for combined bearing and bypass loading with damage developing in the net-section tension mode. However, the compression bearing-bypass strength showed an unexpected interaction involving the bearing mode.

Crews, J. H., Jr.↗
NASA NTRS1989

Prediction of fatigue-crack growth in a high-strength aluminum alloy under variable-amplitude loading

The present paper is concerned with the application of an analytical crack-closure model to study crack growth under various load histories. The model was based on a crack-tip plasticity concept like the Dugdale model, but modified to leave plastically deformed material in the wake of the advancing crack tip. The effect of material thickness on plasticity was accounted for by using a constraint factor on tensile yielding at the crack tip. The model was used to correlate crack-growth rates under constant-amplitude loading, and to predict crack growth under variable-amplitude loading on a high-strength aluminum alloy (7475-T7351) sheet material. The experimental data were obtained from Zhang et al. Predicted crack-growth lives agreed well with experimental data. For ten crack-growth tests subjected to various variable-amplitude load histories, the ratio of predicted-to-experimental lives ranged from 0.54 to 1.19. The mean value of the ratio of predicted-to-experimental lives was 0.95 and the standard error was 0.2 using a constraint factor of 1.9 in the model. Crack-opening stresses calculated from the model were significantly different from those determined by Zhang et al. using a striation-based experimental method.

Newman, J. C., Jr.↗
NASA NTRS1989

Structural materials for space applications

The long-term performance of structural materials in the space environment is a key research activity within NASA. The primary concerns for materials in low Earth orbit (LEO) are atomic oxygen erosion and space debris impact. Atomic oxygen studies have included both laboratory exposures in atomic oxygen facilities and flight exposures using the Shuttle. Characterization of atomic oxygen interaction with materials has included surface recession rates, residual mechanical properties, optical property measurements, and surface analyses to establish chemical changes. The Long Duration Exposure Facility (LDEF) is scheduled to be retrieved in 1989 and is expected to provide a wealth of data on atomic oxygen erosion in space. Hypervelocity impact studies have been conducted to establish damage mechanisms and changes in mechanical properties. Samples from LDEF will be analyzed to determine the severity of space debris impact on coatings, films, and composites. Spacecraft placed in geosynchronous Earth orbit (GEO) will be subjected to high doses of ionizing radiation which for long term exposures will exceed the damage threshold of many polymeric materials. Radiation interaction with polymers can result in chain scission and/or cross-linking. The formation of low molecular weight products in the epoxy plasticize the matrix at elevated temperatures and embrittle the matrix at low temperatures. This affects both the matrix-dominated mechanical properties and the dimensional stability of the composite. Embrittlement of the matrix at low temperatures results in enhanced matrix microcracking during thermal cycling. Matrix microcracking changes the coefficient of thermal expansion (CTE) of composite laminates and produces permanent length changes. Residual stress calculations were performed to estimate the conditions necessary for microcrack development in unirradiated and irradiated composites. The effects of UV and electron exposure on the optical properties of transparent polymer films were also examined to establish the optimum chemical structure for good radiation resistance. Thoughts on approaches to establishing accelerated testing procedures are discussed.

Tenney, Darrel R.↗
NASA NTRS1990

Second order tensor finite element

The results of a research and software development effort are presented for the finite element modeling of the static and dynamic behavior of anisotropic materials, with emphasis on single crystal alloys. Various versions of two dimensional and three dimensional hybrid finite elements were implemented and compared with displacement-based elements. Both static and dynamic cases are considered. The hybrid elements developed in the project were incorporated into the SPAR finite element code. In an extension of the first phase of the project, optimization of experimental tests for anisotropic materials was addressed. In particular, the problem of calculating material properties from tensile tests and of calculating stresses from strain measurements were considered. For both cases, numerical procedures and software for the optimization of strain gauge and material axes orientation were developed.

Oden, J. Tinsley↗
NASA NTRS1991

Fracture mechanics analysis for various fiber/matrix interface loadings

Fiber/matrix (F/M) cracking was analyzed to provide better understanding and guidance in developing F/M interface fracture toughness tests. Two configurations, corresponding to F/M cracking at a broken fiber and at the free edge, were investigated. The effects of mechanical loading, thermal cooldown, and friction were investigated. Each configuration was analyzed for two loadings: longitudinal and normal to the fiber. A nonlinear finite element analysis was performed to model friction and slip at the F/M interface. A new procedure for fitting a square-root singularity to calculated stresses was developed to determine stress intensity factors (K sub I and K sub II) for a bimaterial interface crack. For the case of F/M cracking at a broken fiber with longitudinal loading, crack tip conditions were strongly influenced by interface friction. As a result, an F/M interface toughness test based on this case was not recommended because nonlinear data analysis methods would be required. For the free edge crack configuration, both mechanical and thermal loading caused crack opening, thereby avoiding frictional effects. A F/M interface toughness test based on this configuration would provide data for K(sub I)/K(sub II) ratios of about 0.7 and 1.6 for fiber and radial normal loading, respectively. However, thermal effects must be accounted for in the data analysis.

Naik, R. A.↗
NASA NTRS1991

Compatible thermal and structural elements for the analysis of beam and plate structures

Energy methods are used to formulate steady-state thermal elements which are compatible with structural beam and plate elements. Comparisons of energy method results with finite element results indicate that the energy methods achieve similar accuracy with fewer degrees of freedom. Limitations of energy methods with regard to discontinuous functions and computational overflow are noted. Thermal stress calculations are simplified by the use of similar formulations for the thermal and structural elements. The advantages that these energy-based elements offer to high-temperature structural optimization are discussed.

Vause, R. F.↗
NASA NTRS1991

Fracture mechanics analysis for various fiber/matrix interface loadings

Fiber/matrix (F/M) cracking was analyzed to provide better understanding and guidance in developing F/M interface fracture toughness tests. Two configurations, corresponding to F/M cracking at a broken fiber and at the free edge, were investigated. The effects of mechanical loading, thermal cooldown, and friction were investigated. Each configuration was analyzed for two loadings: longitudinal and normal to the fiber. A nonlinear finite element analysis was performed to model friction and slip at the F/M interface. A new procedure for fitting a square-root singularity to calculated stresses was developed to determine stress intensity factors (K sub I and K sub II) for a bimaterial interface crack. For the case of F/M cracking at a broken fiber with longitudinal loading, crack tip conditions were strongly influenced by interface friction. As a result, an F/M interface toughness test based on this case was not recommended because nonlinear data analysis methods would be required. For the free edge crack configuration, both mechanical and thermal loading caused crack opening, thereby avoiding frictional effects. An F/M interface toughness test based on this configuration would provide data for K(sub I)/K(sub II) ratios of about 0.7 and 1.6 for fiber and radial normal loading, respectively. However, thermal effects must be accounted for in the data analysis.

Naik, R. A.↗
NASA NTRS1992

Raman scattering of InGaAs/InP grown by uniform radial flow epitaxy

Uniform radial flow epitaxy, a novel growth technique, has been used to grown InGaAs films on InP. Epitaxial layers above and below the critical thickness for the onset of slip were grown. Raman spectroscopy was used to characterize the quality of epitaxial layers, determine alloy composition, and measure the strain. Raman spectra from both pseudomorphic (strained) and relaxed (unstrained) InGaAs films were obtained at 300 and 80 K. The difference in the frequencies of their GaAs-like longitudinal optical phonons was used to calculate stress for the strained InGaAs/InP, leading to a direct formula for the evaluation of the layer stress.

Feng, Z. C.↗
NASA NTRS1992

Fracture mechanics analysis for various fiber/matrix interface loadings

Fiber/matrix (F/M) cracking was analyzed to provide better understanding and guidance in developing F/M interface fracture toughness tests. Two configurations, corresponding to F/M cracking at a broken fiber and at the free edge, were investigated. The effects of mechanical loading, thermal cooldown, and friction were investigated. Each configuration was analyzed for two loadings: longitudinal and normal to the fiber. A nonlinear finite element analysis was performed to model friction and slip at the F/M interface. A new procedure for fitting a square-root singularity to calculated stresses was developed to determine stress intensity factors (K sub I and K sub II) for a bimaterial interface crack. For the case of F/M cracking at a broken fiber with longitudinal loading, crack tip conditions were strongly influenced by interface friction. As a result, an F/M interface toughness test based on this case was not recommended because nonlinear data analysis methods would be required. For the free edge crack configuration, both mechanical and thermal loading caused crack opening, theory avoiding fractional effects. A F/M interface toughness test based on this configuration would provide data for K(sub I/K(sub II) ratios of about 0.7 and 1.6 for fiber and radial normal loading, respectively. However, thermal effects must be accounted for in the data analysis.

Naik, Rajiv A.↗
NASA NTRS1937

Strain measurements on small duralumin box beams in bending

Extensive strain-gage measurements were made chiefly on the tension side of five small rectangular box beams constructed of sheet duralumin. The main conclusion was that within the test range the tension cover may be considered as being fully effective but that at any given point on the beam there may be unaccountable variations of 5 percent from the calculated stresses on the thicker sheets tested (0.044 and 0.023 inch) and of 10 percent or more on the thinnest sheet tested (0.014 inch).

Kuhn, Paul↗
NASA NTRS1993

Extensional history of Mars' Tharsis Region

Graben structures in the outer part of Mars' Tharsis region follow calculated stress patterns that are based on Tharsis topographic and gravity anomalies and flexural response of the lithosphere. However, Tharsis extension is not evenly distributed - most extension is concentrated in the Alba, Tempe, Valles Marineris, and Syria-Thaumasia volcanotectonic provinces. Preliminary results suggest that the overall extension of Tharsis produced by loading is about 8 km (based on the assumption that the Sirenum province exemplifies the overall extension of Tharsis), whereas the total circumferential extension of the Tharsis region estimated thus far is about 33 km (an estimate was not made for the Syria-Thaumasia province, and evidence in some other areas may be buried). It is concluded that local tectonism, possibly caused by intrusion and passive and active rifting, produced most of the extension in the Tharsis region.

Tanaka, Kenneth L.↗
NASA NTRS1994

Variations of a global constraint factor in cracked bodies under tension and bending loads

Elastic-plastic finite-element analyses were used to calculate stresses and displacements around a crack in finite-thickness plates for an elastic-perfectly plastic material. Middle- and edge-crack specimens were analyzed under tension and bending loads. Specimens were 1.25 to 20 mm thick with various widths and crack lengths. A global constraint factor alpha(sub g), an averaged normal-stress to flow-stress ratio over the plastic region, was defined to simulate three-dimensional (3D) effects in two-dimensional (2D) models. For crack lengths and uncracked ligament lengths greater than four times the thickness, the global constraint factor was found to be nearly a unique function of a normalized stress-intensity factor (related to plastic-zone size to thickness ratio) from small- to large-scale yielding conditions for various specimen types and thickness. For crack length-to-thickness ratios less than four, the global constraint factor was specimen type, crack length and thickness dependent. Using a 2D strip-yield model and the global constraint factors, plastic-zone sizes and crack-tip displacements agreed reasonably well with the 3D analyses. For a thin sheet aluminum alloy, the critical crack-tip-opening angle during stable tearing was found to be independent of specimen type and crack length for crack length-to-thickness ratios greater than 4.

Newman, J. C., Jr.↗
NASA NTRS2001

Consideration of Moving Tooth Load in Gear Crack Propagation Predictions

Robust gear designs consider not only crack initiation, but crack propagation trajectories for a fail-safe design. In actual gear operation, the magnitude as well as the position of the force changes as the gear rotates through the mesh. A study to determine the effect of moving gear tooth load on crack propagation predictions was performed. Two-dimensional analysis of an involute spur gear and three-dimensional analysis of a spiral-bevel pinion gear using the finite element method and boundary element method were studied and compared to experiments. A modified theory for predicting gear crack propagation paths based on the criteria of Erdogan and Sih was investigated. Crack simulation based on calculated stress intensity factors and mixed mode crack angle prediction techniques using a simple static analysis in which the tooth load was located at the highest point of single tooth contact was validated. For three-dimensional analysis, however, the analysis was valid only as long as the crack did not approach the contact region on the tooth.

Lewicki, David G.↗
NASA NTRS1984

Velocity Vector Analysis of a Juncture Flow Using a Three-Component Laser Velocimeter

A specialized single-axis, five-beam three-component laser velocimeter was constructed and used to study the flow field in a juncture. The juncture was defined by a blunt leading, edged vertical splitter plate and a sharp leading edged horizontal plate. The investigations were conducted in the Low Turbulence Pressure Tunnel at a Mach number of 0.1 and a Reynolds number of 2.2 x 10(exp 6) per meter over the model. The three-component velocity flow field in the juncture was measured, Reynolds stresses calculated and the velocity vector analysis performed.

Meyers, James F.↗