A biaxial fatigue test rig using four large hydraulic actuators was equipped with a superimposed wave generation function in order to conduct fatigue tests simulating complex loading from multiple directions on the hull structure. As a result of the operation confirmation of this system using the cruciform specimen, it was confirmed that the center point of the specimen was retained, and that the in-plane bending did not occur in the specimen, and that only the load in the axial direction was accurately loaded. The application of this system to the fatigue crack propagation test was verified, and it was possible to control with a constant error rate even if the rigidity changed by the crack growth, and good test results were obtained.
