Accession Number : AD0470299

Title :   MECHANISMS OF FATIGUE IN 1100-0 AND 2024-T4 ALUMINUM.

Descriptive Note : Final technical rept. 1 Apr 64-31 Mar 65,

Corporate Author : MIDWEST RESEARCH INST KANSAS CITY MO

Personal Author(s) : Grosskreutz,J. C. ; Shaw,G. G.

Report Date : JUL 1965

Pagination or Media Count : 37

Abstract : The mechanisms of fatigue in notched 1100-0 and 2024-T4 aluminum have been studied by means of optical and electron microscopy. It was found that fatigue cracks nucleated at slip bands on the surface of 1100-0 aluminum in less than 0.5% of total fatigue life. These slip-band fissure cracks grew independently for 65 - 70% of life and then linked rather quickly into a dominant crack which accounted for final failure. The crack growth rates were recorded for both fissure and dominant cracks. On the surface of 2024-T4 aluminum, cracks nucleated in pairs at constituent particle inclusions in less than 5% of total fatigue life. At low stresses, a single crack-pair grew across the notch in about 90% of life and accounted for complete failure as it continued across the sample face. At high stresses, many crack-pairs were nucleated in the notch, some of which linked to form a dominant crack at about 50% of life. Crack extension in both 1100-0 and 2024-T4 aluminum was observed to occur by a heterogeneous mixture of ripple formation, ductile and cleavage fracture which occurs noncoherently at local regions along the crack front. Some of the consequences of this observation for crack propagation theories are discussed. (Author)

Descriptors :   (*ALUMINUM ALLOYS, FATIGUE(MECHANICS)), (*FATIGUE(MECHANICS), ALUMINUM), ELECTRON MICROSCOPY, FRACTURE(MECHANICS), PROPAGATION, FRACTOGRAPHY, STRESSES, NUCLEATION

Distribution Statement : APPROVED FOR PUBLIC RELEASE