The fatigue loading tests were accomplished using the MTSLandmark 370.50 hydraulic servo fatigue test machine (MTS) with500 kN capacity. Firstly, two high-strength bolts were screwed by hand(negligible preload) into the upper and lower holes of the sphere, respectively,and the depth of the bolt threads screwed into the sphere is1.1 times of the bolt nominal diameter (approximately 10 threads).Then, the assembled specimen was installed on the MTS loading device,and the head of each bolt was directly clamped to the fixture of the MTS. Secondly, the position of the specimen was adjusted carefully toensure the coaxiality between the specimen and the clamps. A generalview of the fatigue loading test configuration is shown in Fig. 6. Finally,each fatigue loading test was ended until the complete failure of thespecimens, and the number of cycles to the failure was then recorded asthe fatigue life of the specimen under testing.