Accession Number : ADA255060

Title :   Spectrum Fatigue Behaviour of Powder Metallurgy Aluminum Alloys.

Descriptive Note : Final rept. Sept 85-Mar 91,

Corporate Author : NORTHROP CORP HAWTHORNE CA AIRCRAFT DIV

Personal Author(s) : Searich, G. V. ; Hahn, M. T.

Report Date : OCT 1991

Pagination or Media Count : 275

Abstract : The fatigue crack growth behavior of three aluminum alloys was examined under constant amplitude and spectrum loading. The fatigue behavior of extrusions and hand forgings of second-generation powder metallurgy (PM) alloy CW67 (X7093) was compared to the fatigue behavior of extrusions of 7091 (a first-generation PM alloy) and 7075 (an ingot metallurgy alloy). Spectrum fatigue crack growth tests were performed using the FALSTAFF fighter spectrum as well as an actual fighter aircraft spectrum. Additionally, overload/underload fatigue crack growth tests were performed to correlate the constant amplitude and spectrum fatigue behaviors. For these tests, overload-induced crack jumps and crack growth retardation were measured. Tensile properties, fracture toughness, stress-life fatigue, and stress corrosion cracking were also evaluated. For the spectrum fatigue tests in particular, the crack growth behavior was correlated to the microstructure and fractography. In summary, the fine-grained PM alloys exhibited significantly higher strengths, toughness, and stress -life fatigue resistance than 7075, but markedly lower constant amplitude fatigue crack growth resistance. Under a tension-dominated FALSTAFF spectrum, PM alloys were generally inferior in crack growth resistance compared to IM alloys, which is consistent with constant amplitude fatigue behavior. However, in spectrums having more compressive loads, Fatigue, Fatigue Crack Growth, Spectrum Fatigue, Overload, FALSTAFF, Powder Metallurgy, Aluminum Alloys, CW67, X7093, 7091, 7075, Stress Corrosion, Fractography.

Descriptors :   *ALUMINUM ALLOYS, *POWDER METALLURGY, *FATIGUE(MECHANICS), AIRCRAFT, ALLOYS, ALUMINUM, AMPLITUDE, BEHAVIOR, CONSTANTS, CORROSION, CRACKS, EXTRUSION, FIGHTER AIRCRAFT, FINES, FORGING, FRACTOGRAPHY, METALLURGY, MICROSTRUCTURE, OVERLOAD, POWDERS, RESISTANCE, RETARDATION, STRESS CORROSION, TENSILE PROPERTIES, TENSION, TEST AND EVALUATION, TOUGHNESS, CRACK PROPAGATION, STRENGTH(MECHANICS), SPECTRA.

Subject Categories : Properties of Metals and Alloys
      Fabrication Metallurgy
      Aircraft

Distribution Statement : APPROVED FOR PUBLIC RELEASE