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At least 181 records · Page 10

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NASA NTRS1972

The influence of temperature on fatigue-crack growth in a mill annealed Ti-6Al-4V alloy

To understand the influence temperature on the rate of fatigue crack growth in high strength metal alloys, constant load amplitude, fatigue crack growth experiments were carried out using a 1/4-inch-thick (6.35 mm) mill annealed Ti-6Al-4V alloy plate as a model material. The rates of fatigue crack growth were determined as a function of temperature, ranging from room temperature to about 290 C (or, about 550 F/563K) and as a function of the crack tip stress intensity factor in a dehumidified high purity argon environment. Limited correlative experiments indicate that dehumidified oxygen and hydrogen have no effect on the rate of fatigue crack growth in this alloy, while distilled water increased the rate of crack growth slightly in the range tested. Companion fractographic examinations suggest that the mechanisms for fatigue crack growth in the various environments are essentially the same.

Wei, R. P.↗

NASA NTRS1971

Fractographic observations of Ti-6Al-4V alloy fatigued in vacuum.

These observations were made as part of a study of the influence of temperature and chemical environment on fatigue-crack growth. The results obtained, along with additional fractographic results in other environments, suggest that the mechanism for fatigue-crack growth in the Ti-6Al-4V alloy is basically similar (striations are observed) for a wide range of environments. In addition to ?vacuum,' these environments include distilled water, ?dry' and ?wet' air, ?dry' hydrogen, and ?dry' and ?wet' argon.

Ritter, D. L.↗

NASA NTRS1972

Hydrogen-enhanced fatigue crack growth in Ti-6Al-4V ELI weldments.

The effects of a hydrogen environment on the fatigue crack growth rates in Ti-6Al-4V ELI (STA) and weld material were determined in the temperature range of ambient to -200 F. The hydrogen environment resulted in an acceleration of the crack growth rate and a change in the fracture mode for both materials in the temperature range of ambient to -100 F. At -200 F, there was no significant difference between the crack growth rates obtained in helium and hydrogen gas. The degree of hydrogen-enhanced crack growth was found to be dependent on the crack tip stress-intensity range, temperature, and microstructure of the material. The data are consistent with an embrittlement mechanism involving hydrogen diffusing ahead of the crack front.

Pittinato, G. F.↗

NASA NTRS1972

SCC of Ti-6Al-4V foil by methanol - Effect of treatments with 2,4-pentanedione and its metal complexes.

The susceptibility of Ti-6Al-4V foil to stress corrosion cracking (SCC) by methanol can be decreased by treatment of the foil with 2,4-pentanedione prior to its immersion in the corroding media. It is assumed that such treatments remove from the protective film formed on the foil by exposure to the atmosphere, certain metal ions whose oxides are more readily penetrated by the ions, Na + and Cl- or Fe(3+) and Cl-, present in the corroding media.

Haney, E. G.↗

NASA NTRS1972

The influence of temperature on fatigue crack growth in a mill annealed Ti-6Al-4V alloy.

To study the influence of temperature on the rate of fatigue crack growth in high strength metal alloys, constant load amplitude fatigue crack growth experiments were carried out using a .25-in.-thick mill annealed Ti-6Al-4V alloy plate. The rates of fatigue crack growth were determined as a function of temperature, ranging from room temperature to about 290 C, and as a function of the crack tip stress intensity factor in a dehumidified high purity argon environment. Limited correlative experiments were carried out in distilled water, dehumidified oxygen and hydrogen, and in vacuum. The results indicate that the rate of fatigue crack growth is essentially independent of test temperature in this alloy, and is affected by residual moisture in very small concentrations. Companion fractographic examinations suggest that the mechanims for fatigue crack growth in the various environments are essentially the same.

Wei, R. P.↗

NASA NTRS1972

Gaseous hydrogen-induced cracking of Ti-5Al-2.5Sn.

Study of the kinetics of hydrogen-induced cracking in the Ti-5Al-2.5Sn titanium alloy, which has a structure of acicular alpha platelets in a beta matrix. The crack-growth rate at low stress-intensity levels was found to be exponentially dependent on stress intensity but essentially independent of temperature. The crack-growth rate at intermediate stress-intensity levels was found to be independent of stress intensity but dependent on temperature in such a way that crack-growth rate was controlled by a thermally activated mechanism having an activation energy of 5500 cal/mole and varied as the square root of the hydrogen pressure. The crack-growth rate at stress-intensity levels very near the fracture toughness is presumed to be independent of environment. The results are interpreted to suggest that crack growth at high stress intensities is controlled by normal, bulk failure mechanisms such as void coalescence and the like. At intermediate stress-intensity levels the transport of hydrogen to some interaction site along the alpha-beta boundary is the rate-controlling mechanism. The crack-growth behavior at low stress intensities suggests that the hydrogen interacts at this site to produce a strain-induced hydride which, in turn, induces crack growth by restricting plastic flow at the crack tip.

Williams, D. P.↗

NASA NTRS1973

Load interaction effects on fatigue crack growth in Ti-6Al-4V alloy

The importance of delay, retardation in the rate of fatigue crack growth, produced by load interactions in variable amplitude loading, on the accurate prediction of fatigue lives of engineering structures is discussed. The effects of a broad range of loading variables on delay in fatigue crack growth at room temperature are examined for a mill annealed Ti-6Al-4V alloy. The results are used to estimate crack growth behavior under programmed loads.

Wei, R. P.↗

NASA NTRS1973

Cracking of Ti-6Al-4V in methanol solutions containing sulfates.

Whether cracking of unnotched Ti-6Al-4V specimens occurs in methanol containing H2SO4, Li2SO4, or Fe2(SO4)3 is a function of the age of the solution and the concentration of the sulfate. With H2SO4 concentrations of 0.10 N to 0.25 N, the methanol solutions lose their ability to crack the specimens with time after mixing and prior to exposure. The aging time required to inhibit the cracking varies inversely with the water content of the solution. With larger quantities of H2SO4, 0.5 N and 1 N, no cracking is observed. Interpretations of Raman spectroscopic studies of the aging solution suggests that the nature of the O-H group may play a role in the crack initiation or inhibiting mechanism.

Haney, E. G.↗

NASA NTRS1973

2s-2p transitions in the spectra of Ca XVII and Ti XIX.

Identifications of energy level transitions in the Ca XVII and Ti XIX spectra in the regions of 190-360 A and 160-300 A, respectively, are presented for the first time. Lines corresponding to the transition arrays concerned are identified and classified. Extrapolation procedures are described in detail.

Goldsmith, S.↗

NASA NTRS1971

The influence of temperature on fatigue-crack growth in a mill-annealed Ti-6Al-4V alloy

To understand the influence of temperature on the rate of fatigue crack growth in high strength metal alloys, constant load amplitude fatigue crack growth experiments were carried out using a 1/4 inch thick (6.35 mm) mill-annealed Ti-6Al-4V alloy plate as a model material. The rates of fatigue crack growth were determined as a function of temperature, ranging from room temperature to about 290 C and as a function of the crack tip, stress intensity factor K, in dehumidified high purity argon environment. The dependence of the rate of fatigue crack growth on K appears to be separable into two regions. The transition correlates with changes in both the microscopic and macroscopic appearances of the fracture surfaces, and suggests a change in the mechanism and the influence of microstructure on fatigue crack growth.

Wei, R. P.↗

NASA NTRS1974

Effect of outdoor exposure at ambient and elevated temperatures on fatigue life of Ti-6Al-4V titanium alloy sheet in the annealed and the solution treated and aged condition

Specimens of Ti-6Al-4V titanium alloy sheet in the annealed and the solution-treated and aged heat-treatment condition were exposed outdoors at ambient and 560 K (550 F) temperatures to determine the effect of outdoor exposure on fatigue life. Effects of exposure were determined by comparing fatigue lives of exposed specimens to those of unexpected specimens. Two procedures for fatigue testing the exposed specimens were evaluated: (1) fatigue tests conducted outdoors by applying 1200 load cycles per week until failure occurred and (2) conventional fatigue tests (continuous cycling until failure occurred) conducted indoors after outdoor exposure under static load. The exposure period ranged from 9 to 28 months for the outdoor fatigue-test group and was 24 months for the static-load group. All fatigue tests were constant-amplitude bending of specimens containing a drilled hole (stress concentration factor of 1.6). The results of the tests indicate that the fatigue lives of solution-treated and aged specimens were significantly reduced by the outdoor exposure at 560 K but not by the exposure at ambient temperature. Fatigue lives of the annealed specimens were essentially unaffected by the outdoor exposure at either temperature. The two test procedures - outdoor fatigue test and indoor fatigue test after outdoor exposure - led to the same conclusions about exposure effects.

Phillips, E. P.↗

NASA NTRS1974

Relation between surface slip topography and stress corrosion cracking in Ti-8 wt % Al

The deformation behavior of Ti-8 wt % Al has been investigated in an inert environment (air), and an aggressive environment (salt water). Details of surface slip geometry were examined by high resolution surface replicas at various stages of deformation in both environments. Specimens aged to contain a fine dispersion of Ti3Al precipitates failed by subcritical crack growth in salt water, whereas specimens in the single phase condition showed no effects of environment on the yield or fracture characteristics. The Ti3Al precipitates produce little change in strength level or slip character compared to the single phase alloy, and there is no evidence of any effects of environment on the character of surface slip. Rather, the presence of trenches along slip bands on the surface of aged specimens suggest that the specific effect of the Ti3Al precipitates is to render the surface slip steps chemically active relative to the surrounding matrix by slip induced dissolution of the particles.

Boyd, J. D.↗

NASA NTRS1973

Combined effects of weld-induced residual stresses and flaws on the fracture strength of Ti-5Al-2.5Sn

The combined effects of weld-induced residual stresses and flaws on fracture strength were experimentally evaluated by testing Ti-5Al-2.5Sn surface flawed specimens at -320F (-195C) in liquid nitrogen. Flaws were located in weld metal with crack planes either parallel to or perpendicular to gas tungsten arc weld centerlines, and in base metal with the crack plane perpendicular to the rolling direction. Tests were conducted using two different flaw sizes to effect fracture stresses at two different levels including one level either at or near, and one level well below the tensile yield strength. Three different residual stress levels were generated, measured, and tested. Results were evaluated using modified linear elastic fracture mechanics theory.

Hall, L. R.↗

NASA NTRS1975

Crack growth in Ti-8Al-1Mo-1V with real-time and accelerated flight by flight loading

Crack growth in Ti-8Al-lMo-lV was measured and calculated for real time and accelerated simulations of supersonic airplane loading and heating. Crack-growth rates calculated on the assumption that an entire flight could be represented by a single cycle predicted the experimental rates poorly. Calculated crack growth rates were slower than the experimental rates for all tests with flight-by-flight loading. For room temperature accelerated tests, the calculated rates agreed well with the experimental rates; but the calculations became progressively less accurate for progressively more complex test conditions (tests that included elevated temperature).

Imig, L. A.↗

NASA NTRS1974

The stability of armalcolite - Experimental studies in the system MgO-Fe-Ti-O

The stability of armalcolite at low pressures is considered, taking into account experiments which confirm the low-temperature breakdown of the mineral. Effects of Al2O3, Cr2O3, and Ti2O3 components on armalcolite stability are discussed with the stability of armalcolite at high pressure. Attention is also given to several reactions involving Fe-Mg-Ti oxides in Apollo 11 and 17 basalts.

Lindsley, D. H.↗

NASA NTRS1974

Abundances of the group IVB elements, Ti, Zr, and Hf and implications of their ratios in lunar materials

New data on Zr and Hf abundances in samples from recent Apollo missions and a few from earlier missions are presented. The data confirm our previous suggestion of a modest Zr-Hf fractionation among lunar rock types. The four major lunar rock types can be readily distinguished, based on Zr and Hf abundances and Zr/Hf mass ratios. Mare basalts exhibit mean Zr abundances ranging from 111 ppm for Apollo 15 to 534 ppm for Apollo 11 and low Zr/Hf mass ratios ranging from 34 to 39. KREEP basalts are characterized by very high Zr contents (mean = 1380 ppm Zr) and high Zr/Hf ratio of 47. Anorthosites exhibit extremely low Zr and Hf contents and possibly very low Zr/Hf ratios. Arguments that the fractionation may be partly due to the presence of Zr(3+) in lunar magmas while Hf remains as Hf(4+) are presented. These data for Zr and Hf together with data for Ti recently obtained on the same samples in our laboratory are discussed in support of a modified two-stage lunar crustal evolution model.

Ehmann, W. D.↗

NASA NTRS1976

Compilation of fatigue, fatigue-crack propagation, and fracture data for 2024 and 7075 aluminum, Ti-6Al-4V titanium, and 300M steel. Volume 1: Description of data and data storage on magnetic tape. Volume 2: Data tape (7-track magnetic tape)

Fatigue, fatigue-crack-propagation, and fracture data compiled and stored on magnetic tape are documented. Data for 202 and 7075 aluminum alloys, Ti-6Al-4V titanium alloy, and 300M steel are included in the compilation. Approximately 4,500 fatigue, 6,500 fatigue-crack-propagation, and 1,500 fracture data points are stored on magnetic tape. Descriptions of the data, an index to the data on the magnetic tape, information on data storage format on the tape, a listing of all data source references, and abstracts of other pertinent test information from each data source reference are included.

Rice, R. C.↗

NASA NTRS1976

Sustained load crack growth design data for Ti-6Al-4V titanium alloy tanks containing hydrazine

Sustained load crack growth data for Ti-6Al-4V titanium alloy in hydrazine per MIL-P-26536 and refined hydrazine are presented. Fracture mechanics data on crack growth thresholds for heat-treated forgings, aged and unaged welds, and aged and unaged heat-affected zones are reported. Fracture mechanics design curves of crack growth threshold stress intensity versus temperature are generated from 40 to 71 C.

Lewis, J. C.↗