Fatigue crack propagation behavior under cyclic tensile or torsional loading with biaxial static
loads has been investigated. Two different biaxial loading systems, i.e. cyclic tensile loading with static
torsional load and cyclic torsional loading with static tensile load, were employed to thin-walled tubular
specimens. The crack propagation was measured by two crack gages mounted near the notch and crack
opening level was measured by unloading compliance method. The directions of the fatigue crack
propagated under respective biaxial loading conditions were examined and the growth rates were
evaluated by using several cyclic parameters, including equivalent stress intensity factor range, Keff,
crack tip opening displacement range, CTD, minimum strain energy density factor range, Smin.
Furthermore, the growth rates were evaluated by effective cyclic parameters considering crack closure. It
was found that the biaxial static stress superimposed on the cyclic tensile or torsional loading tests has no
influence on the propagation directions of the cracks. Furthermore, it was shown that the fatigue crack
growth rates under biaixial faigue loading were well expressed by using the cyclic fatigue parameters,
Keq,eff, CTDeff, Smin,eff considering crack closure effect.
Discrete variable optimization of structures subjected to dynamic loads using equivalent static loads and metaheuristic algorithms