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  • METALLIC MATERIALS  (4)
  • Metallic Materials  (1)
  • 1
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    Unknown
    Effect of service usage on tensile, fatigue, and fracture properties of 7075-T6 and 7178-T6 aluminum alloys (1975)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A study has been made to determine the effects of extensive service usage on some basic material properties of 7075-T6 and 7178-T6 aluminum alloy materials. The effects of service usage were determined by comparing material properties for new material (generally obtained from the literature) with those for material cut from the center wing box of a C-130B transport airplane with 6385 flight-hours of service. The properties investigated were notched and unnotched fatigue strengths, fatigue-crack-growth rate, fracture toughness, and tensile properties. For the properties investigated and the parameter ranges considered (crack length, stress ratio, etc.), the results obtained showed no significant difference between service and new materials.
    Keywords: METALLIC MATERIALS
    Type: NASA-TM-X-3165 , L-9952
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Fatigue mechanics - An assessment of a unified approach to life prediction (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Consideration is given to the development of a total-life prediction methodology for aerospace structures based solely on crack propagation from a microstructural defect at stress concentrations. Crack-growth lives were calculated for a given loading condition by integrating the crack-growth-rate-against-delta K relationships for crack growth from a microstructural defect size to failure. Both small- and large-crack growth rate data were used. The assessment was based on data on 2024-T3 aluminum alloy, 2090-T8E41 aluminum-lithium alloy, annealed Ti-6Al-4V titanium alloy, and high-strength 4340 steel under either constant-amplitude or spectrum loading. Good agreement was found between fatigue lives measured on notched specimens with those computed from the total-life analysis.
    Keywords: METALLIC MATERIALS
    Type: Advances in Fatigue Lifetime Predictive Techniques; Apr 24, 1990; San Francisco, CA; United States
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Unknown
    Fatigue crack initiation and small crack growth in several airframe alloys (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The growth of naturally-initiated small cracks under a variety of constant amplitude and variable amplitude load sequences is examined for several airframe materials: the conventional aluminum alloys, 2024-T3 and 7075-T6, the aluminum-lithium alloy, 2090-T8E41 and 4340 steel. Loading conditions investigated include constant amplitude loading at R = 0.5, 0, -1 and -2 and the variable amplitude sequences FALSTAFF, Mini-TWIST, and FELIX/28. Crack growth was measured at the root of semicircular edge notches using acetate replicas. Crack growth rates are compared on a stress intensity factor basis, to those for large cracks to evaluate the extent of the small crack effect in each alloy. In addition, the various alloys are compared on a crack initiation and crack growth morphology basis.
    Keywords: METALLIC MATERIALS
    Type: Fatigue 90: International Conference on Fatigue and Fatigue Thresholds; Jul 15, 1990 - Jul 20, 1990; Honolulu, HI; United States
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    NASA TECHNICAL REPORTS
  • 4
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    Fatigue Analyses Under Constant- and Variable-Amplitude Loading Using Small-Crack Theory (1999)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: Studies on the growth of small cracks have led to the observation that fatigue life of many engineering materials is primarily "crack growth" from micro-structural features, such as inclusion particles, voids, slip-bands or from manufacturing defects. This paper reviews the capabilities of a plasticity-induced crack-closure model to predict fatigue lives of metallic materials using "small-crack theory" under various loading conditions. Constraint factors, to account for three-dimensional effects, were selected to correlate large-crack growth rate data as a function of the effective stress-intensity factor range (delta-Keff) under constant-amplitude loading. Modifications to the delta-Keff-rate relations in the near-threshold regime were needed to fit measured small-crack growth rate behavior. The model was then used to calculate small-and large-crack growth rates, and to predict total fatigue lives, for notched and un-notched specimens under constant-amplitude and spectrum loading. Fatigue lives were predicted using crack-growth relations and micro-structural features like those that initiated cracks in the fatigue specimens for most of the materials analyzed. Results from the tests and analyses agreed well.
    Keywords: Metallic Materials
    Type: NASA/TM-1999-209329 , L-17862 , ARL-TR-2001 , NAS 1.15:209329
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 5
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    The growth of small cracks in 4340 steel (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: 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.
    Keywords: METALLIC MATERIALS
    Type: National Technical Specialists'' Meeting on Advanced Rotorcraft Structures; Oct 25, 1988 - Oct 27, 1988; Williamsburg, VA; United States
    Format: text
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    NASA TECHNICAL REPORTS
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