Engineering topics

Kantzos, Pete

Publications and source records attributed to Kantzos, Pete.

12 records

NASA NTRS2006

Burst Testing and Analysis of Superalloy Disks With a Dual Grain Microstructure

Elastic-plastic finite element analyses of room temperature burst tests on four superalloy disks were conducted and reported in this paper. Two alloys, Rene 104 (General Electric Aircraft Engines) and Alloy 10 (Honeywell Engines & Systems), were studied. For both alloys an advanced dual microstructure disk, fine grain bore and coarse grain rim, were analyzed and compared with conventional disks with uniform microstructures, coarse grain for Rene 104 and fine grain for Alloy 10. The analysis and experimental data were in good agreement up to burst. At burst, the analysis underestimated the speed and growth of the Rene 104 disks, but overestimated the speed and growth of the Alloy 10 disks. Fractography revealed that the Alloy 10 disks displayed significant surface microcracking and coalescence in comparison to Rene 104 disks. This phenomenon may help explain the differences between the Alloy 10 disks and the Rene 104 disks, as well as the observed deviations between analytical and experimental data at burst.

Gayda, John↗

NASA NTRS2005

Cyclic Spin Testing of Superalloy Disks With a Dual Grain Microstructure

An aggressive cyclic spin test program was run to verify the reliability of superalloy disks with a dual grain structure, fine grain bore and coarse grain rim, utilizing a disk design with web holes bisecting the grain size transition zone. Results of these tests were compared with conventional disks with uniform grain structures. Analysis of the test results indicated the cyclic performance of disks with a dual grain structure could be estimated to a level of accuracy which does not appear to prohibit the use of this technology in advanced gas turbine engines, although further refinement of lifing methodology is clearly warranted.

Gayda, John↗

NASA NTRS2003

The Effect of Heat Treatment on the Fatigue Behavior of Alloy 10

The results of the fatigue evaluation on Alloy 10, run under NASA's Ultrasafe Project, are the subject of this report. Crack growth evaluation will be examined in a separate report. The eight heat treatments studied were designed to evaluate the effect of solution temperature, cooling rate, and stabilization on key mechanical properties of Alloy 10, including fatigue life. Two temperatures were studied, 750 and 1300 F, which represent projected application temperatures for the bore and rim locations in a disk. In addition to fatigue life, the cyclic stress-strain response and failure modes of the fatigue specimens are also reviewed in this report.

Gayda, John↗

NASA NTRS2003

Low Cost Heat Treatment Process for Production of Dual Microstructure Superalloy Disks

There are numerous incidents where operating conditions imposed on a component mandate different and distinct mechanical property requirements from location to location within the component. Examples include a crankshaft in an internal combustion engine, gears for an automotive transmission, and disks for a gas turbine engine. Gas turbine disks are often made from nickel-base superalloys, because these disks need to withstand the temperature and stresses involved in the gas turbine cycle. In the bore of the disk where the operating temperature is somewhat lower, the limiting material properties are often tensile and fatigue strength. In the rim of the disk, where the operating temperatures are higher than those of the bore, because of the proximity to the combustion gases, resistance to creep and crack growth are often the limiting properties.

Gayda, John↗

NASA NTRS2002

Quench Crack Behavior of Nickel-base Disk Superalloys

There is a need to increase the temperature capability of superalloy turbine disks to allow higher operating temperatures in advanced aircraft engines. When modifying processing and chemistry of disk alloys to achieve this capability, it is important to preserve the ability to use rapid cooling during supersolvus heat treatments to achieve coarse grain, fine gamma prime microstructures. An important step in this effort is an understanding of the key variables controlling the cracking tendencies of nickel-base disk alloys during quenching from supersolvus heat treatments. The objective of this study was to investigate the quench cracking tendencies of several advanced disk superalloys during simulated heat treatments. Miniature disk specimens were rapidly quenched after solution heat treatments. The responses and failure modes were compared and related to the quench cracking tendencies of actual disk forgings. Cracking along grain boundaries was generally observed to be operative. For the alloys examined in this study, the solution temperature not alloy chemistry was found to be the primary factor controlling quench cracking. Alloys with high solvus temperatures show greater tendency for quench cracking.

Gayda, John↗

NASA NTRS2002

Ceramic Inclusions In Powder Metallurgy Disk Alloys: Characterization and Modeling

Powder metallurgy alloys are increasingly used in gas turbine engines, especially as the material chosen for turbine disks. Although powder metallurgy materials have many advantages over conventionally cast and wrought alloys (higher strength, higher temperature capability, etc.), they suffer from the rare occurrence of ceramic defects (inclusions) that arise from the powder atomization process. These inclusions can have potentially large detrimental effect on the durability of individual components. An inclusion in a high stress location can act as a site for premature crack initiation and thereby considerably reduce the fatigue life. Because these inclusions are exceedingly rare, they usually don't reveal themselves in the process of characterizing the material for a particular application (the cumulative volume of the test bars in a fatigue life characterization is typically on the order of a single actual component). Ceramic inclusions have, however, been found to be the root cause of a number of catastrophic engine failures. To investigate the effect of these inclusions in detail, we have undertaken a study where a known population of ceramic particles, whose composition and morphology are designed to mimic the 'natural' inclusions, are added to the precursor powder. Surface connected inclusions have been found to have a particularly large detrimental effect on fatigue life, therefore the volume of ceramic 'seeds' added is calculated to ensure that a minimum number will occur on the surface of the fatigue test bars. Because the ceramic inclusions are irregularly shaped and have a tendency to break up in the process of extrusion and forging, a method of calculating the probability of occurrence and expected intercepted surface and embedded cross-sectional areas were needed. We have developed a Monte Carlo simulation to determine the distributions of these parameters and have verified the simulated results with observations of ceramic inclusions found in macro slices from extrusions and forgings. The ultimate goal of this study will be to use probabilistic methods to determine the reliability detriment that can be attributed to these ceramic inclusions.

Bonacuse, Pete↗

NASA NTRS2002

Burst Testing of a Superalloy Disk with a Dual Grain Structure

Room temperature burst testing of an advanced nickel-base superalloy disk with a dual grain structure was conducted. The disk had a fine grain bore and a coarse grain rim. The results of this test showed that the disk burst at 39,100 rpm in line with predictions based on a 2-D finite element analysis. Further, significant growth of the disk was observed before failure which was also in line with predictions.

Gayda, John↗

NASA NTRS2002

High Temperature Spin Testing of a Superalloy Disk With a Dual Grain Structure

Comparative spin tests were run on superalloy disks at an elevated temperature to determine the benefits of a DMHT disk, with a fine grain bore and coarse grain rim, versus a traditional subsolvus disk with a fine grain structure in the bore and rim. The results of these tests showed that the DMHT disk exhibited significantly lower growth at 1500 F. Further, the results of these tests could be accurately predicted using a 2D viscoelastic finite element analysis. These results indicate DMHT technology can be used to extend disk operating temperatures when compared to traditional subsolvus heat treatment options for superalloy disks. However, additional research is required to ensure the safe operation of a DMHT disk under more realistic engine operating conditions. This includes testing to determine the burst margin and cyclic capability of DMHT disks in a spin pit, at a minimum, and ultimately running an engine test with a DMHT disk.

Gayda, John↗

NASA NTRS1997

Characterization of Damage Accumulation in a C/SiC Composite at Elevated Temperatures

This research is part of a program aimed to evaluate and demonstrate the ability of candidate CMC materials for a variety of applications in reusable launch vehicles. The life and durability of these materials in rocket and engine applications are of major concern and there is a need to develop and validate life prediction methodology. In this study, material characterization and mechanical testing was performed in order to identify the failure modes, degradation mechanisms, and progression of damage in a C/SiC composite at elevated temperatures. The motivation for this work is to provide the relevant damage information that will form the basis for the development of a physically based life prediction methodology.

Telesman, Jack↗

NASA NTRS1995

Fatigue Crack Growth and Crack Bridging in SCS-6/Ti-24-11

Interfacial damage induced by relative fiber/matrix sliding was found to occur in the bridged zone of unidirectional SCS-6/Ti-24Al-11Nb intermetallic matrix composite specimens subjected to fatigue crack growth conditions. The degree of interfacial damage was not uniform along the bridged crack wake. Higher damage zones were observed near the machined notch in comparison to the crack tip. The interfacial friction shear strength tau(sub f) measured in the crack wake using pushout testing revealed lower values than the as-received interface. Interfacial wear also reduced the strength of the bridging fibers. The reduction in fiber strength is thought to be a function of the magnitude of relative fiber/matrix displacements ind the degree of interfacial damage. Furthermore, two different fiber bridging models were used to predict the influence of bridging on the fatigue crack driving force. The shear lag model required a variable tau(sub f) in the crack wake (reflecting the degradation of the interface) before its predictions agreed with trends exhibited by the experimental data. The fiber pressure model did an excellent job in predicting both the FCG data and the DeltaCOD in the bridged zone even though it does not require a knowledge of tau(sub f).

Ghosn, Louis J.↗

NASA NTRS1992

Modeling of crack bridging in a unidirectional metal matrix composite

The effective fatigue crack driving force and crack opening profiles were determined analytically for fatigue tested unidirectional composite specimens exhibiting fiber bridging. The crack closure pressure due to bridging was modeled using two approaches: the fiber pressure model and the shear lag model. For both closure models, the Bueckner weight function method and the finite element method were used to calculate crack opening displacements and the crack driving force. The predicted near crack tip opening profile agreed well with the experimentally measured profiles for single edge notch SCS-6/Ti-15-3 metal matrix composite specimens. The numerically determined effective crack driving force, Delta K(eff), was calculated using both models to correlate the measure crack growth rate in the composite. The calculated Delta K(eff) from both models accounted for the crack bridging by showing a good agreement between the measured fatigue crack growth rates of the bridged composite and that of unreinforced, unbridged titanium matrix alloy specimens.

Ghosn, Louis J.↗

NASA NTRS1991

Modeling of crack bridging in a unidirectional metal matrix composite

The effective fatigue crack driving force and crack opening profiles were determined analytically for fatigue tested unidirectional composite specimens exhibiting fiber bridging. The crack closure pressure due to bridging was modeled using two approaches; the fiber pressure model and the shear lag model. For both closure models, the Bueckner weight function method and the finite element method were used to calculate crack opening displacements and the crack driving force. The predicted near crack tip opening profile agreed well with the experimentally measured profiles for single edge notch SCS-6/Ti-15-3 metal matrix composite specimens. The numerically determined effective crack driving force, Delta K(sup eff), was calculated using both models to correlate the measure crack growth rate in the composite. The calculated Delta K(sup eff) from both models accounted for the crack bridging by showing a good agreement between the measured fatigue crack growth rates of the bridged composite and that of unreinforced, unbridged titanium matrix alloy specimens.

Ghosn, Louis J.↗