Accession Number : AD0692166

Title :   ENVIRONMENTAL FATIGUE CRACK PROPAGATION OF ALUMINUM ALLOYS AT LOW STRESS INTENSITY LEVELS.

Descriptive Note : Research rept.,

Corporate Author : BOEING CO RENTON WASH COMMERCIAL AIRPLANE DIV

Personal Author(s) : Feeney,J. A. ; McMillan,J. C. ; Wei,R. P.

Report Date : MAY 1969

Pagination or Media Count : 30

Abstract : The environmental fatigue crack propagation in 2024-T3, 7075-T6, and 7178-T6 was studied at low levels of cyclic amplitude of stress intensity, delta K. Both wedge force loading and remote loading techniques were employed to achieve the desired delta K levels, and preliminary experiments were designed to test their compatibility. Testing was carried out in humid air, distilled water, and 3.5% sodium chloride solution, and the observed crack growth rates compared with those in desiccated air. Later studies were also conducted in an inert reference environment with a total water content of less than 2 ppm. When the data are plotted as log delta K versus log d2a/dN, alloy 2024-T3 exhibits a marked slope transition, alloy 7075-T6 a slight slope transition, and alloy 7178-T6 a rectilinear behavior throughout the whole range of delta K studied. The basic shape of these curves is discussed in terms of state-of-stress conditions at the crack tip, frequency effects, environmental effects, strain rate sensitivity, and metallurgical structure. An attempt is also made to correlate the rate of fatigue crack propagation in a particular environment and at a particular delta K level with the fracture topography. (Author)

Descriptors :   (*ALUMINUM ALLOYS, CRACK PROPAGATION), (*FATIGUE(MECHANICS), ALUMINUM ALLOYS), ENVIRONMENTAL TESTS, FRACTURE(MECHANICS), FRACTOGRAPHY, STRESSES

Subject Categories : Metallurgy and Metallography
      Mechanics

Distribution Statement : APPROVED FOR PUBLIC RELEASE