Accession Number : ADA182949

Title :   Fatigue behavior of Long and Short Cracks in Aluminum Alloys.

Descriptive Note : Final rept. 15 Apr 84-14 Apr 87,

Corporate Author : CALIFORNIA UNIV BERKELEY DEPT OF MATERIALS SCIENCE AND MINERAL ENGINEERING

Personal Author(s) : Ritchie,Robert O ; Yu,Weikang

PDF Url : ADA182949

Report Date : 01 May 1987

Pagination or Media Count : 198

Abstract : The fatigue behavior of short cracks, which are small compared to the scale of the microstructure, small compared to the scale of local plasticity or simply physically small (i.e., 1 mm), must be considered as one of the major factors limiting the application of defect-tolerant fatigue design for airframe and engine components. Accordingly, this program was aimed at identifying factors which govern the growth of such short cracks (in contrast to long cracks) in a series of commercial aluminum alloys, with specific reference to behavior at near threshold levels. Based on experiments in 2124, 7150 and 2090 alloys, it is shown that whereas the behavior of long cracks at near threshold levels is largely controlled by the magnitude of the crack tip shielding from crack closure and deflection mechanisms, short crack growth rates are invariably faster because of their inability to develop shielding due to their limited wake. Experiments whereby the wake material is physically removed confirm such notions and indicate that the predominant closure forces are located close (within 500 um) of the tip. Keywords: Fatigue; Defect-tolerant fatigue design; Variable amplitude loading; Fatigue in aluminum alloys; Fatigue behavior of long and short cakes; Fatigue cracks; Crack closure.

Descriptors :   *ALUMINUM ALLOYS, *CRACKS, CLOSURES, DEFLECTION, FATIGUE(MECHANICS), WAKE, LEVEL(QUANTITY), THRESHOLD EFFECTS, MICROSTRUCTURE, CONTRAST, SHIELDING, ENGINE COMPONENTS, PLASTIC PROPERTIES, SCALE, FOOD, CRACK PROPAGATION, RATES, SHORT RANGE(TIME), AMPLITUDE, VARIABLES, MATERIALS

Subject Categories : Properties of Metals and Alloys

Distribution Statement : APPROVED FOR PUBLIC RELEASE