NTRS - NASA Technical Reports Server
fatigue crack closure behavior at high stress ratiosFatigue crack delay behavior at high stress ratio caused by single peak overloads was investigated in two thicknesses of 7475-T731 aluminum alloy. Closure measurements indicated no closure occurred before or throughout the overload plastic zones following the overload. This was further substantiated by comparing the specimen compliance following the overload with the compliance of a low R ratio test when the crack was fully open. Scanning electron microscope studies revealed that crack tunneling and possibly reinitiation of the crack occurred, most likely a result of crack-tip blunting. The number of delay cycles was greater for the thinner mixed mode stress state specimen than for the thicker plane strain stress state specimen, which is similar to low R ratio test results and may be due to a larger plastic zone for the mixed mode cased.
Turner, C. Christopher (General Motors Corp. Inland Div., Dayton, OH, United States) Carman, C. Davis (General Dynamics Corp. Fort Worth, TX, United States) Hillberry, Ben M. (Purdue University West Lafayette, IN, United States)
August 14, 2013
January 1, 1988