SEDL / STP / STP833-EB / STP32558S

Fatigue Crack Growth Behavior of 7XXX Aluminum Alloys under Simple Variable Amplitude Loading

Bretz, PE
Senior Engineer, Staff Scientist, Technical Specialist, and Senior Materials Analyst, Alloy Technology Division, Aluminum Company of America, Alcoa Center, Pa.

Vasudévan, AK
Senior Engineer, Staff Scientist, Technical Specialist, and Senior Materials Analyst, Alloy Technology Division, Aluminum Company of America, Alcoa Center, Pa.

Bucci, RJ
Senior Engineer, Staff Scientist, Technical Specialist, and Senior Materials Analyst, Alloy Technology Division, Aluminum Company of America, Alcoa Center, Pa.

Malcolm, RC
Senior Engineer, Staff Scientist, Technical Specialist, and Senior Materials Analyst, Alloy Technology Division, Aluminum Company of America, Alcoa Center, Pa.

Pages: 24    Published: Jan 1984

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Abstract

This investigation examines the influence of temper and purity on the fatigue crack growth (FCG) behavior of four 7XXX aluminum alloys (7075-T6, 7075-T7, 7050-T6, 7050-T7) tested using a periodic single overload spectrum at low stresses. The loading sequence consists of a periodic single overload spike occurring once every 8000 constant amplitude cycles; the overload spike is 1.8 times the constant amplitude load peak. All tests have been performed in high humidity (>90% relative humidity) air at a frequency of 20 Hz and a constant amplitude load ratio of R = 0.33. The observed microstructural effects on transient (that is, spectrum) FCG behavior are contrasted with those for steady-state (constant load amplitude) fatigue performance.