High Low Sequence Research Articles

Fatigue-Crack-Propagation Rates Under Random Excitation

Fatigue-crack-propagation rates have been measured for 2024-T3 aluminum cantilever beams in reversed bending under constant amplitude, two-level constant amplitude, and random excitations. For the two-level tests there is a large interaction between the crack-propagation rates caused by stress cycles of different amplitudes. The high-low sequence gives a delay and the low-high sequence a higher rate than a simple no interaction assumption would predict. This is confirmed in the random-excitation tests where the crack-propagation rate for low damping is much higher than that for high damping for exactly the same distribution and level of stress peaks.