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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Engine cyclic durability by analysis and material testing

The problem of calculating turbine engine component durability is addressed. Nonlinear, finite-element structural analyses, cyclic constitutive behavior models, and an advanced creep-fatigue life prediction method called strainrange partitioning were assessed for their applicability to the solution of durability problems in hot-section components of gas turbine engines. Three different component or subcomponent geometries are examined: a stress concentration in a turbine disk; a louver lip of a half-scale combustor liner; and a squealer tip of a first-stage high-pressure turbine blade. Cyclic structural analyses were performed for all three problems. The computed strain-temperature histories at the critical locations of the combustor linear and turbine blade components were imposed on smooth specimens in uniaxial, strain-controlled, thermomechanical fatigue tests of evaluate the structural and life analysis methods.

Kaufman, A.↗
NASA NTRS1984

High-Temperature Cyclic Oxidation Data, Volume 1

This first in a series of cyclic oxidation handbooks contains specific-weight-change-versus-time data and X-ray diffraction results derived from high-temperature cyclic tests on high-temperature, high-strength nickel-base gamma/gamma' and cobalt-base turbine alloys. Each page of data summarizes a complete test on a given alloy sample.

Barrett, C. A.↗
NASA NTRS1983

The effects of Cr, Al, Ti, Mo, W, Ta, and Cb on the cyclic oxidation behavior of cast Ni-base superalloys at 1100 and 1150 C

Fifty Ni-base superalloys with concentrations of Cr, Al, Ti, Mo, W, Ta, and Cb systematically varied between two nonzero levels, were tested for cyclic oxidation resistance at 1100 and 1150 C. Oxidation resistance was interpreted in terms of the rate of specific weight change and the types of oxides formed. It is found that the resistance of the alloys to cyclic oxidation is largely determined by Al content, with a sharp increase in the oxidation resistance observed in the Al concentration range 5-8 at. pct. The effects of the other elements studied were small compared with that of aluminum. Best oxidation resistance characteristics were predicted for high Al (13 at. pct), low Cr (10 at. pct), low Ti (2 at. pct), low Cb (1 at. pct), and high Mo, W, and Ta (3 at. pct each). The effects of the refractory metals, however, are somewhat ambiguous and should be investigated further. Higher boron contents, which were unintentionally varied, were clearly detrimental even for the most resistant compositions.

Barrett, C. A.↗
NASA NTRS1983

NASTRAN forced vibration analysis of rotating cyclic structures

Theoretical aspects of a new capability, developed and added to the general purpose finite element program NASTRAN Level 17.7, to conduct forced vibration analysis of turned cyclic structures rotating about their axis of symmetry, are presented. The effects of Coriolis and centripetal accelerations as well as those due to the translational acceleration of the axis of rotation, are included. The equations of motion are first derived for an arbitrary grid point of the cyclic sector finite element model and then extended for the complete model. The equations are solved by four principal steps: (1) transformation of applied loads at frequency-dependent circumferential harmonic components; (2) application of circumferential harmonic-dependent intersegment compatibility constraints; (3) solution of frequency-dependent circumferential harmonic components of displacements; and (4) recovery of frequency-dependent response in various segments of the total structure. Five interrelated examples are presented to illustrate the various features of the development.

Elchuri, V.↗
NASA NTRS1984

Engine cyclic durability by analysis and material testing

The problem of calculating turbine engine component durability is addressed. Nonlinear, finite-element structural analyses, cyclic constitutive behavior models, and an advanced creep-fatigue life prediction method called strainrange partitioning were assessed for their applicability to the solution of durability problems in hot-section components of gas turbine engines. Three different component or subcomponent geometries are examined: a stress concentration in a turbine disk; a louver lip of a half-scale combustor linear; and a squealer tip of a first-stage high-pressure turbine blade. Cyclic structural analyses were performed for all three problems. The computed strain-temperature histories at the critical locations of the combustor linear and turbine blade components were imposed on smooth specimens in uniaxial, strain-controlled, thermomechanical fatigue tests of evaluate the structural and life analysis methods.

Kaufman, A.↗
NASA NTRS1985

Cyclic structural analyses of anisotropic turbine blades for reusable space propulsion systems

Turbine blades for reusable space propulsion systems are subject to severe thermomechanical loading cycles that result in large inelastic strains and very short lives. These components require the use of anisotropic high-temperature alloys to meet the safety and durability requirements of such systems. To assess the effects on blade life of material anisotropy, cyclic structural analyses are being performed for the first stage high-pressure fuel turbopump blade of the space shuttle main engine. The blade alloy is directionally solidified MAR-M 246 alloy. The analyses are based on a typical test stand engine cycle. Stress-strain histories at the airfoil critical location are computed using the MARC nonlinear finite-element computer code. The MARC solutions are compared to cyclic response predictions from a simplified structural analysis procedure developed at the NASA Lewis Research Center.

Manderscheid, J. M.↗
NASA NTRS1985

Seasonal, diurnal, and solar cyclical variations of the limiting H(+) flux in the earth's topside ionosphere

Seasonal and solar cyclical variations in the limiting H(+) flux are compared over the solar minimum-to-maximum interval 1974-80. The comparisons are made on the bases of values derived with the MSIS-83 and -77 models, which in turn are based on Atmospheric Explorer-E O(+) and H(+) data from the ionosphere. The H(+) flux is obtained by integration of the H(+) continuity equation along magnetic flux tubes. The seasonal and cyclical variations are dominated by the neutral hydrogen density, although the O(+) boundary density, scale height and O(+)-H reaction somewhat ameliorate the changes caused by the density variations. Finally, the plasmasphere experienced an order of magnitude decrease in H(+) in going from solar minimum to maximum, which could have been caused by longer limiting flux escapes through more, longer-lived, shorter flux tubes.

Richards, P. G.↗
NASA NTRS1983

Validation of structural analysis methods using burner liner cyclic rig test data

The objectives of the hot section technology (HOST) burner liner cyclic rig test program are basically threefold: (1) to assist in developing predictive tools needed to improve design analyses and procedures for the efficient and accurate prediction of burner liner structural response; (2) to calibrate, evaluate and validate these predictive tools by comparing the predicted results with the experimental data generated in the tests; and (3) to evaluate existing as well as advanced temperature and strain measurement instrumentation, both contact and noncontact, in a simulated engine cycle environment. The data generated will include measurements of the thermal environment (metal surface temperatures) as well as structural (strain) and life (fatigue) responses of simulated burner liners and specimens under controlled boundary and operating conditions. These data will be used to calibrate, compare and validate analytical theories, methodologies and design procedures, as well as improvements in them, for predicting liner temperatures, stress-strain responses and cycles to failure. Comparison of predicted results with experimental data will be used to show where the predictive theories, etc. need improvements. In addition, as the predictive tools, as well as the tests, test methods, and data acquisition and reduction techniques, are developed and validated, a proven, integrated analysis/experiment method will be developed to determine the cyclic life of a simulated burner liner.

Thompson, R.↗
NASA NTRS1985

Fatigue Damage in Notched Composite Laminates Under Tension-Tension Cyclic Loads

The results are given of an investigation to determine the damage states which develop in graphite epoxy laminates with center holes due to tension-tension cyclic loads, to determine the influence of stacking sequence on the initiation and interaction of damage modes and the process of damage development, and to establish the relationships between the damage states and the strength, stiffness, and life of the laminates. Two quasi-isotropic laminates were selected to give different distributions of interlaminar stresses around the hole. The laminates were tested under cyclic loads (R=0.1, 10 Hz) at maximum stresses ranging between 60 and 95 percent of the notched tensile strength.

Stinchcomb, W. W.↗
NASA NTRS1986

Cyclic creep analysis from elastic finite-element solutions

A uniaxial approach was developed for calculating cyclic creep and stress relaxation at the critical location of a structure subjected to cyclic thermomechanical loading. This approach was incorporated into a simplified analytical procedure for predicting the stress-strain history at a crack initiation site for life prediction purposes. An elastic finite-element solution for the problem was used as input for the simplified procedure. The creep analysis includes a self-adaptive time incrementing scheme. Cumulative creep is the sum of the initial creep, the recovery from the stress relaxation and the incremental creep. The simplified analysis was exercised for four cases involving a benchmark notched plate problem. Comparisons were made with elastic-plastic-creep solutions for these cases using the MARC nonlinear finite-element computer code.

Kaufman, A.↗
NASA NTRS1986

Experimental evaluation criteria for constitutive models of time dependent cyclic plasticity

Notched members were tested at temperatures far above those recorded till now. Simulation of the notch root stress response was accomplished to establish notch stress-strain behavior. Cyclic stress-strain profiles across the net-section were recorded and on-line direct notch strain control was accomplished. Data are compared to three analysis techniques with good results. The objective of the study is to generate experimental data that can be used to evaluate the accuracy of constitutive models of time dependent cyclic plasticity.

Martin, J. F.↗
NASA NTRS1985

Microgravity changes in heart structure and cyclic-AMP metabolism

The effects of microgravity on cardiac ultrastructure and cyclic AMP metabolism in tissues of rats flown on Spacelab 3 are reported. Light and electron microscope studies of cell structure, measurements of low and high Km phosphodiesterase activity, cyclic AMP-dependent protein kinase activity, and regulatory subunit compartmentation show significant deviations in flight animals when compared to ground controls. The results indicate that some changes have occurred in cellular responses associated with catecholamine receptor interactions and intracellular signal processing.

Philpott, D. E.↗
NASA NTRS1987

FPT Algorithm for Two-Dimensional Cyclic Convolutions

Fast-polynomial-transform (FPT) algorithm computes two-dimensional cyclic convolution of two-dimensional arrays of complex numbers. New algorithm uses cyclic polynomial convolutions of same length. Algorithm regular, modular, and expandable.

Truong, Trieu-Kie↗
NASA NTRS1986

Fatigue response of notched laminates subjected to tension-compression cyclic loads

The fatigue response of a ((0/45/90/-45)(sub s))(sub 4) T300-5208 graphite-epoxy laminate with a drilled center-hole subjected to various components of tensile and compressive cyclic loads was investigated. Damage evaluation techniques such as stiffness monitoring, penetrant-enhanced X-ray radiography, C-scan, laminate deply and residual strength measurement were used to establish the mechanisms of damage development as well as the effect of such damage on the laminate strength, stiffness and life. Damage modes consisted of transverse matrix cracks, initiating at the hole, in all plies, followed by delamination between plies of different orientation. A characteristic stiffness repsonse during cyclic loading at two load levels was identified and utilized a more reliable indicator of material and residual properties than accumulated cycles. For the load ratios of tension-compression loading, residual tensile strength increased significantly above the virgin strength early in the fatigue life and remained approximately constant to near the end of life. A technique developed for predicting delamination initiation sites along the hole boundary correlated well with experimental evidence.

Bakis, C. E.↗
NASA NTRS1987

Influence of electron radiation and temperature on the cyclic, matrix dominated response of graphite-epoxy

The effects of electron radiation and elevated temperature on the matrix-dominated cyclic response of standard T300/934 and a chemically modified T300/934 graphite-epoxy are characterized. Both materials were subjected to 1.0 x 10 to the 10th rads of 1.0 MeV electron irradiation, under vacuum, to simulate 30 years in geosynchronous orbit. Cyclic tests were performed at room temperature and elevated temperature (121 C) on 4-ply unidirectional laminates to characterize the effects associated with irradiation and elevated temperature. Both materials exhibited energy dissipation in their response at elevated temperature. The irradiated modified material also exhibited energy dissipation at room temperature. The combination of elevated temperature and irradiation resulted in the most severe effects in the form of lower proportional limits, and greater energy dissipation. Dynamic-mechanical analysis demonstrated that the glass transition temperature, T(g), of the standard material was lowered 39 C by irradiation, wereas the T(g) of the modified material was lowered 28 C by irradiation. Thermomechanical analysis showed the occurrence of volatile products generated upon heating of the irradiated materials.

Reed, Susan M.↗
NASA NTRS1988

Cyclic uniaxial and biaxial hardening of type 304 stainless steel modeled by the viscoplasticity theory based on overstress

The isotropic theory of viscoplasticity based on overstress does not use a yield surface or a loading and unloading criterion. The inelastic strain rate depends on overstress, the difference between the stress and the equilibrium stress, and is assumed to be rate dependent. Special attention is paid to the modeling of elastic regions. For the modeling of cyclic hardening, such as observed in annealed Type 304 stainless steel, and additional growth law for a scalar quantity which represents the rate independent asymptotic value of the equilibrium stress is added. It is made to increase with inelastic deformation using a new scalar measure which differentiates between nonproportional and proportional loading. The theory is applied to correlate uniaxial data under two step amplitude loading including the effect of further hardening at the high amplitude and proportional and nonproportional cyclic loadings. Results are compared with corresponding experiments.

Yao, David↗
NASA NTRS1986

Thermal cyclic durability testing of ceramic materials for turbine engines

The thermal cyclic durability of commercial ceramic materials for turbine engines was under evaluation since 1978. Ceramic materials are exposed to cyclic diesel-fired burner exhaust at either 1204 or 1371 C (2200 or 2500 F) for up to 3500 hours. The test conditions are selected to simulate the environment experienced by the hot flow path components in an automotive gas turbine engine. The silicon nitride and silicon carbide materials tested are the same ceramic materials currently used on the AGT100 and AGT101 ceramic turbine engine program.

Lindberg, L. J.↗
NASA NTRS1988

On the cyclic stress-strain behaviour of a Ni-base superalloy at room temperature

The cyclic stress-strain behavior of Nimonic alloy PE16 was studied at room temperature and at different aging conditions to determine whether the plateau in the cyclic stress-strain curve (CSSC) reported by Arbuthnot (1982) is typical of the room temperature behavior and/or some specific initial microstructural states. Specimen blanks were heat-treated in batches in Ar/H2 (98/2) atmosphere to produce gamma-prime precipitates of different average sizes, but with the volume fraction of gamma-prime precipitates kept constant at about 7 percent at all the heat-treatment conditions. Total axial strain controlled LCF tests were conducted under fully reversed loading (R = -1) at a constant strain rate of 0.004/s, using a servohydraulic machine. The load response in tension and compression was recorded continually, and stress-strain hysteresis loops were recorded at frequent intervals. In the present investigation, the CSSCs of the P16 alloy at room temperature did not display the plateaus reported by Arbuthnot.

Singh, Vakil↗