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NASA NTRS1988

The growth of small cracks in 4340 steel

A semiempirical crack-growth model incorporating crack-closure effects has been used to predict crack growth rates and total fatigue life in notched specimens of 4340 steel having an initial defect typical of those previously noted in this steel upon subjection to both constant-amplitude and spectrum loadings. Model predictions for fatigue life are found to be in reasonable agreement with experiments and, in particular, the model was able to accurately predict total fatigue life for specimens subjected to the 'Felix/28' spectrum loading sequence on the sole basis of constant-amplitude test test results.

Swain, M. H.↗

NASA NTRS1988

Ignition of steel alloys by impact of low-velocity iron/inert particles in gaseous oxygen

The ignition of carbon steel and 316 and 304 stainless steels caused by the impact of low-velocity particles (a standard mixture consisting of 2 g of iron and 3 g of inert materials) in gaseous oxygen was investigated using NASA/White Sands Test Facility for the ignition test, and a subsonic particle impact chamber to accelerate the particles that were injected into flowing oxygen upstream of the target specimen. It was found that the oxygen velocities required to ignite the three alloys were the same as that required to ignite the particle mixture. Ignition occurred at oxygen velocities greater than 45 m/sec at 20 to 24 MPa and was found to be independent of pressure between 2 and 30 MPa. Comparison of the present results and the past results from Wegener (1964) with the Compressed Gas Association (CGA) oxygen velocity limits for safe operations indicates that the CGA limits may be excessively conservative at high pressures and too liberal at low pressures.

Benz, Frank J.↗

NASA NTRS1988

Wear of liquid nitrogen-cooled 440C bearing steels in an oxygen environment

This paper presents up-to-date findings of the research being conducted to understand the mechanism of sliding wear in unlubricated 440C bearing steels under oxidative conditions. A sliding wear test rig has been designed and built with a cylinder-on-flat geometry. The equipment is capable of testing specimens under high axial loads and sliding speeds in a simulated LOX environment. Samples of 440C steel, quenched and tempered to a hardness of Rc 56, were tested under a load of 890 N and a sliding speed of 2.05 m/sec for total sliding distances of up to 5.54 km. Flash temperatures during these tests were measured with an IR camera and a fast digital recorder. Microstructural and microanalytical data from the worn surfaces and the debris particles are analyzed extensively, along with wear rates, flash temperatures, surface profiles, hardnesses, and residual stresses, in the context of oxidation and wear theories.

Chaudhuri, Dilip K.↗

NASA NTRS1989

Rapid rotational/translational maneuvering experiments of a flexible steel beam

Future space manipulators may need translational base motion to expand the access region of a manipulator. An experiment was conducted to demonstrate slewing of flexible structures with coupled rotational and translational axes while simultaneously suppressing vibrational motion during the maneuver. In the experiment, a flexible steel beam carried by a translational cart was maneuvered by an active controller to perform position-control tasks. Experimental results are presented to show how the flexibility of the steel beam influences the multi-input multi-output feedback controller.

Juang, Jer-Nan↗

NASA NTRS1988

Surface metallurgical and tribological characteristics of TiN-coated bearing steels

The rolling contact fatigue (RCF) characteristics of an aerospace bearing steel 440C coated with TiN films of various thicknesses are studied. The wear and corrosion properties of the film-substrate system are examined as well as how these properties correlate with the RCF behavior. It is found that TiN coatings with thicknesses below 1 micron resulted in significant improvements in the RCF lives of base steel substrates under both mild and heavy loading conditions.

Erdemir, A.↗

NASA NTRS1990

Nondestructive Technique To Assess Embrittlement In Steels

Recent research at NASA Langley Research Center led to identification of nondestructive technique for detection of temper embrittlement in HY80 steel. Measures magnetoacoustic emission associated with reversible motion of domain walls at low magnetic fields. Of interest to engineers responsible for reliability and safety of various dynamically loaded and/or thermally cycled steel parts. Applications include testing of landing gears, naval vessels, and parts subjected to heat, such as those found in steam-pipe fittings, boilers, turbine rotors, and nuclear pressure vessels.

Allison, Sidney G.↗

NASA NTRS1992

Casting Stainless-Steel Models Around Pressure Tubes

Survivability of thin-wall stainless-steel tubing increased to nearly 100 percent. Improves state of art in pressure-model castings and reduces cost associated with machining complete model from stainless-steel blank.

Vasquez, Peter↗

NASA NTRS1992

Electrochemical Impedance Of Inorganic-Zinc-Coated Steel

Report describes preliminary experiments to evaluate both direct-current and alternating-current electrochemical impedance measurements as candidate techniques for use in accelerated corrosion testing of mild-steel panels coated with inorganic zinc-rich primers and exposed to seaside air. Basic idea behind experiments to compare electrochemical impedance measurements with anticorrosion performances of coating materials to determine whether measurements can be used to predict performances. Part of continuing program to identify anticorrosion coating materials protecting steel panels adequately for as long as 5 years and beyond.

Macdowell, Louis G.↗

NASA NTRS1990

Application of magnetoacoustic emission technique to temper embrittlement characterization of HY-80 steel

Magnetoacoustic phenomena associated with the use of the magnetoacoustic emission technique for the temper embrittlement characterization of HY-80 steel are investigated in an attempt to explain some peculiarities observed in highly embrittled HY-80 samples. In particular, attention is given to the effects of the ac magnetic field frequency and shape. The peak amplitude of the magnetoacoustic burst, which is directly related to the width of the pulse height distribution, is shown to be a critical parameter in the determination of the degree of temper embrittlement in the steel.

Denale, R.↗

NASA NTRS1993

Improved Heat Treatment Of Steel Alloy 4340

New process takes significantly less time than prior heat-treatment processes. Involves placing steel plate directly in furnace and heat-treating. Plate then quenched in slowly moving oil to reduce stresses. Any deflection then pressed out. Possible uses of 4340 steel include new and improved bulletproof vests for military and police personnel and armor for bulletproof automobiles for military, police, diplomatic, and private users. Also used in other military land vehicles as tanks and in both military and civilian aircraft. Lighter armorplate enables land vehicles and aircraft to attain greater speed and maneuverability, consume less fuel, and afford better protection from snipers or terrorists.

Cooper, Lawrence B.↗

NASA NTRS1993

Stress corrosion evaluation of HP 9Ni-4Co-0.30C steel plate welds

A stress corrosion cracking (SCC) investigation was conducted on HP 9Ni-4Co-0.30C steel plate welds (welded by using straight polarity plasma arc and HP 9Ni-4Co-0.20C weld wire) since this material is being considered for use in the Advanced Solid Rocket Motor (ASRM) program. Prior to the welding, the material was double tempered at 538 C (1,000 F). After welding, only part of the material was stress relieved at 510 C (950 F) for 3 h. Round tensile specimens obtained from nonstress-relieved material were tested in 100-percent relative humidity at 38 C (100 F), in 3.5-percent NaCl alternate immersion, and in 5-percent salt spray at 35 C (95 F). Specimens obtained from stress-relieved material were tested in alternate immersion. The stress levels were 50, 75, and 90 percent of the corresponding 0.2-percent yield strength (YS). All the nonstress-relieved specimens exposed to salt spray and alternate immersion failed. Stress-relieved specimens (exposed to alternate immersion) failed at 75 and 90 percent of YS. No failures occurred at 50 percent of YS in the stress-relieved specimens which indicates a beneficial effect of the stress relief on the SCC resistance of these welds. The stress relief also had a positive effect on the mechanical properties of the welds (the most important being an increase of 21 percent on the YS). Under the conditions of these tests, the straight polarity plasma are welded HP 9Ni4Co-0.30C steel plate was found highly susceptible to SCC in the nonstress-relieved condition. This susceptibility to SCC was reduced by stress relieving.

Torres, Pablo D.↗

NASA NTRS1943

Round Heat-treated Chromium-molybdenum-steel Tubing Under Combined Loads

The results of tests of round heat-treated chromium-molybdenum-steel tubing are presented. Tests were made on tubing under axial load, bending load, torsional load, combined bending and axial load, combined bending and torsional load, and combined axial, bending, and torsional load. Tensile and compressive tests were made to determine the properties of the material. Formulas are given for the evaluation of the maximum strength of this steel tubing under individual or combined loads. The solution of an example is included to show the procedure to be followed in designing a tubular cantilever member to carry combined loads.

Osgood, William R↗

NASA NTRS1952

An engineering method for estimating notch-size effect in fatigue tests on steel

Neuber's proposed method of calculating a practical factor of stress concentration for parts containing notches of arbitrary size depends on the knowledge of a "new material constant" which can be established only indirectly. In this paper, the new constant has been evaluated for a large variety of steels from fatigue tests reported in the literature, attention being confined to stresses near the endurance limit. Reasonably satisfactory results were obtained with the assumption that the constant depends only on the tensile strength of the steel. Even in cases where the notches were cracks of which only the depth was known, reasonably satisfactory agreement was found between calculated and experimental factors. It is also shown that the material constant can be used in an empirical formula to estimate the size effect on unnotched specimens tested in bending fatigue.

Kuhn, Paul↗

NASA NTRS1945

Nitrited-Steel Piston Rings for Engines of High Specific Power

Stability and control characteristics determined from tests in the Langley 19-foot pressure tunnel of a 0.2375-scale model of the Douglas XA-26 airplane are compared with those measured in flight tests of a Douglas A-26b airplane. Several designs of nitrided-steel piston rings were performance-tested under variable conditions of output. The necessity of good surface finish and conformity of the ring to the bore was indicated in the preliminary tests. Nitrided-steel rings of the same dimensions as cast-iron rings operating on the original piston were unsatisfactory, and the final design was a lighter, rectangular, thin-face-width ring used on a piston having a maximum cross-head area and a revised skirt shape. Results were obtained from single-cylinder and multicylinder engine runs.

Collins, John H↗

NASA NTRS1993

Stress corrosion cracking properties of 15-5PH steel

Unexpected occurrence of failures, due to stress corrosion cracking (SCC) of structural components, indicate a need for improved characterization of materials and more advanced analytical procedures for reliably predicting structures performance. Accordingly, the purpose of this study was to determine the stress corrosion susceptibility of 15-5PH steel over a wide range of applied strain rates in a highly corrosive environment. The selected environment for this investigation was a highly acidified sodium chloride (NaCl) aqueous solution. The selected alloy for the study was a 15-5PH steel in the H900 condition. The slow strain rate technique was selected to test the metals specimens.

Rosa, Ferdinand↗

NASA NTRS1994

Mechanical behavior of precipitation hardenable steels exposed to highly corrosive environment

Unexpected occurrences of failures, due to stress corrosion cracking (SCC) of structural components, indicate a need for improved characterization of materials and more advanced analytical procedures for reliably predicting structures performance. Accordingly, the purpose of this study was to determine the stress corrosion susceptibility of 15 - 5 PH steel over a wide range of applied strain rates in a highly corrosive environment. The selected environment for this investigation was a 3.5 percent NaCl aqueous solution. The material selected for the study was 15 - 5 PH steel in the H 900 condition. The Slow Strain Rate technique was used to test the metallic specimens.

Rosa, Ferdinand↗

NASA NTRS1961

Effect of Decarburization on Notch Sensitivity and Fatigue-Crack-Propagation Rates in 12 MoV Stainless-Steel Sheet

Tests were conducted in order to determine the effect of surface decarburization on the notch sensitivity and rate of fatigue crack propagation in 12 MoV stainless-steel sheet at room temperature. Three specimen configurations were utilized in the course of the investigation: standard tensile specimen, 9-inch-wide specimens containing fatigue cracks or thread-cut notches of 0.005-inch radius, and 2-inch-wide specimens containing fatigue cracks. The 12 MoV stainless-steel sheet in the normal condition was found to have an ultimate tensile strength of 251 ksi and to be extremely notch sensitive. The material in the decarburized condition was found to have an ultimate tensile strength of 210 ksi and to be considerably stronger than the normal material in the presence of fatigue cracks. Decarburization did not appear to have any significant influence on the rate of fatigue crack propagation in the 2-inch-wide specimens at the stress levels considered. In addition to the tests, two methods for predicting residual static strength and their application to the material are discussed.

Herrnstein, William H., III↗

NASA NTRS2001

The Effects of Shot and Laser Peening on Fatigue Life and Crack Growth in 2024 Aluminum Alloy and 4340 Steel

Fatigue and crack growth tests have been conducted on 4340 steel and 2024-T3 aluminum alloy, respectively, to assess the effects of shot peening on fatigue life and the effects of shot and laser peening on crack growth. Two current programs involving fixed and rotary-wing aircraft will not be using shot peened structures. Since the shot peening compressive residual stress depth is usually less than the 0.05-inch initial damage tolerance crack size, it is believed by some that shot peening should have no beneficial effects toward retarding crack growth. In this study cracks were initiated from an electronic-discharged machining flaw which was cycled to produce a fatigue crack of approximately 0.05-inches in length and then the specimens were peened. Test results showed that after peening the crack growth rates were noticeably slower when the cracks were fairly short for both the shot and laser peened specimens resulting in a crack growth life that was a factor of 2 to 4 times greater than the results of the average unpeened test. Once the cracks reached a length of approximately 0.1-inches the growth rates were about the same for the peened and unpeened specimens. Fatigue tests on 4340 steel showed that the endurance limit of a test specimen with a 0.002-inch-deep machining-like scratch was reduced by approximately 40 percent. However, if the "scratched" specimen was shot peened after inserting the scratch, the fatigue life returned to almost 100 percent of the unflawed specimens original fatigue life.

Everett, R. A., Jr.↗