Synergy effects in the fatigue crack growth of hole cold expanded specimens under variable cyclic loading

Abstract The influence of variable load spectra in the fatigue crack growth (FCG) was analyzed. A 4.1% interference was pre-set to some specimens by an expansion operation. As-drilled hole and hole expanded specimens were subjected to FCG tests under a combination of baseline cyclic loading and periodic overloads or underloads applied. Fatigue life was of approximately 1 million of cycles for the as-drilled hole, and 3.5 million of cycles for the hole cold expanded. The pre-setting operation and variable load spectra interaction exhibited a synergy, which was associated with multiple periods of retardation and arresting observed in the crack growth rate.