Fatigue Crack Growth, Arrest, and Reinitiation along a Row of Holes.

摘要

Fatigue crack growth along a row of fastener-sized holes in 7075-T6 Aluminum sheet is investigated experimentally and analytically. The cracking sequence is punctuated by substantial periods of crack reinitiation with each arrestment at a hole. Two methods for estimating the duration of these crack reinitiation periods are developed and compared with the test data. The use of crack nucleation data and theory for such estimation appears to more closely predict test results than the use of fracture mechanics analysis with an assumed .005 inch preexisting microcrack. (This conclusion is relevant to the 'continuing damage analysis' requirements in the Air Force's 'Damage Tolerance Design Requirements'.) Some new formulas for stress concentration factors and stress intensity factors are presented. Further, the discussion of the significance of the elastic stress field near a long notch is offered which may have useful implications for fatigue analysis.