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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS2011

The J-2X Fuel Turbopump - Turbine Nozzle Low Cycle Fatigue Acceptance Rationale

The J-2X Fuel Turbopump (FTP) turbine, which drives the pump that feeds hydrogen to the J-2X engine for main combustion, is based on the J-2S design developed in the early 1970 s. Updated materials and manufacturing processes have been incorporated to meet current requirements. This paper addresses an analytical concern that the J-2X Fuel Turbine Nozzle Low Cycle Fatigue (LCF) analysis did not meet safety factor requirements per program structural assessment criteria. High strains in the nozzle airfoil during engine transients were predicted to be caused by thermally induced stresses between the vane hub, vane shroud, and airfoil. The heritage J-2 nozzle was of a similar design and experienced cracks in the same area where analysis predicted cracks in the J-2X design. Redesign options that did not significantly impact the overall turbine configuration were unsuccessful. An approach using component tests and displacement controlled fracture mechanics analysis to evaluate LCF crack initiation and growth rate was developed. The results of this testing and analysis were used to define the level of inspection on development engine test units. The programmatic impact of developing crack initiation/growth rate/arrest data was significant for the J-2X program. Final Design Certification Review acceptance logic will ultimately be developed utilizing this test and analytical data.

Hawkins, Lakiesha V.↗
NASA NTRS1984

Oxidation and low cycle fatigue life prediction

When a metallic material is exposed to a high temperature in an ambient atmosphere, oxidation takes place on the metallic surface. The formed oxides (both surface and grain boundary oxides) are mechanically brittle so that if the stress is high enough the oxides will be cracked. The grain boundary oxide formation in TAZ-8A nickel-base superalloy was studied. The effect of oxide crack nucleus on low cycle fatigue life will be analyzed. The TAZ-8A was subjected to high temperature oxidation tests in air under the stress-free condition. The oxidation temperatures were 600, 800, and 1000 C. The oxidation time varies from 10 to 1000 hours.

Oshida, Y.↗
NASA NTRS1988

A nonlinear history-dependent damage model for low cycle fatigue

A nonlinear damage postulate that embodies the dependence of the damage rate on cycle-dependent changes in the bulk microstructure and the surface topography is examined. The postulate is analytically formulated in terms of the deformation history dependence of the bulk behavior. This formulation is used in conjunction with baseline data in accordance with the damage postulate to predict the low cycle fatigue resistance of OFE copper. Close comparison of the predictions with experimentally observed behavior suggests that the postulate offers a viable basis for nonlinear damage analysis.

Leis, B. N.↗
NASA NTRS1983

Low cycle fatigue behavior of aluminum/stainless steel composites

Composites consisting of an aluminum matrix reinforced with various volume fractions of stainless steel wire were fabricated by hot die pressing under various conditions of temperature, time, and pressure. The composites were tested in plane bending to complete fracture under cycle loading, and the results were analyzed on a computer to obtain a statistically valid mathematical relationship between the low-cycle fatigue life and the fiber volume fraction of the composite. The fractured surfaces of the composites were examined by scanning electron microscopy to identify the characteristic features of fatigue damage. Fatigue damage mechanisms are proposed and discussed.

Bhagat, R. B.↗
NASA NTRS1984

A history dependent damage model for low cycle fatigue

This paper examines damage assessment and accumulation. A nonlinear damage postulate is advanced that embodies the dependence of the damage rate on cycle-dependent changes in the bulk microstructure and the surface topography. The postulate is analytically formulated in terms of the deformation history dependence of the bulk behavior. This formulation is used in conjunction with baseline data in accordance with the damage postulate to predict the low cycle fatigue resistance of OFE copper. Close comparison of the predictions with observed behavior suggests the postulate offers a viable basis for nonlinear damage analysis.

Leis, B. N.↗
NASA NTRS2001

Advanced Finite Element Modeling of Low Cycle Fatigue Crack Growth

This document (a viewgraph presentation) assumes a crack-like defect of a size which may be missed in inspection will exist in most critical location of any critical structure or component. Flaw existence assumption is usually, but not always, conservative based on past experiences in NASA and knowledge of manufacturing processes. Cyclic, environmental, and sustained loads used to generate stresses on models. Fracture Mechanics analysis used to predict crack growth and residual strength. Must show that defective structure will still provide four times required mission lifetime. Special exemptions cover redundant structures, low risk parts, etc. Assessments require specialized software tools, experienced analysts, and reliable material crack growth rate test database.

Gregg, Wayne↗
NASA NTRS1990

The effect of hydrogen on the low cycle fatigue behavior of a single crystal superalloy

The present study compares the room temperature fatigue properties of PWA 1480 single crystals containing either normal or elevated hydrogen levels, giving attention to the effects of various levels of HIPing process-controlled porosity on hydrogen-trapping and fatigue life. Hydrogen charging is found to degrade the fatigue lives of alloy samples by an order of magnitude; the magnitude of this degradation is comparable at both high and low porosity. HIPing accomplished a small beneficial effect on the fatigue life of both the hydrogen-charged and uncharged PWA 1480 samples. Fatigue cracks are noted to have consistently initiated at large, near-surface pores. By reducing the size and frquency of the larger pores, HIPing apparently retarded fatigue-crack initiation.

Gayda, J.↗
NASA NTRS1972

On the cyclic stress-strain behavior and low cycle fatigue of aerospace materials

The elastic-plastic deformation behavior under cyclic stress of a number of different engineering materials was experimentally investigated with the aid of high-precision methods of measuring, some of which had been newly developed. Experiments made with a variety of steels, the titanium alloy Ti-A16-V4, a cobalt (tungsten) alloy, the high-temperature material Nimonic 90 and Dural (A1-Cu) are reported. The theory given in an attempt to explain these experiments is aimed at finding general formulas for the cyclic stress-strain behavior materials.

Burbach, J.↗
NASA NTRS1975

Strainrange partitioning: A tool for characterizing high temperature low cycle fatigue

The basic concepts of strain range partitioning are reviewed and the areas requiring for expanded verification are detailed. A suggested cooperative evaluation program involves the verification of the four basic life relationships (for PP, CC, PC, and CP type inelastic strain ranges) for a variety of materials that are of direct interest to the participating organizations.

Hirschberg, M. H.↗