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An understanding of conditions that trigger the loosening of bolted joints is essential to ensure joint reliability. In this study, a three-dimensional finite element model of a typical bolted joint is developed, and a new simulation method is proposed to quantitatively identify the critical transverse force for initiating loosening. This force is used to evaluate the anti-loosening capacity of bolted joints. Using the proposed simulation method, the effects of factors affecting critical loosening are systematically studied. It is found that the preload, frictional coefficients at the thread and the bearing surfaces, clamped length, and fit tolerance mainly affected loosening. When the preload and friction coefficients are increased, and the clamped length and fit tolerance are reduced, loosening is inhibited. Experiments are performed to demonstrate the reliability of the results. Finally, a suggestion is proposed to improve the design guideline VDI 2230 for bolted joints, which considers the requirement of avoiding loosening under vibrational loading.

Using earthquake data recorded by seismic stations in the eastern China and Taiwan areas, Japan and Ryukyu Arcs, we reconstructed the P wave velocity structure of the eastern China seas and adjacent areas through a seismic tomography inversion. By analyzing the properties of lithosphere mantle and deep dynamic conditions in these regions, we discussed the locations of the boundaries between the Sino-Korea, Yangtze and South China blocks. They revealed the effects of the collision of Philippine Sea plate with Eurasian continent, slab subduction, and back-arc extension on the lithosphere structure of the eastern China seas. The results also revealed a strong lateral heterogeneity of the lithosphere mantle in the eastern China seas and it has a certain relation with regional tectonics. The Wulian-Qingdao fault zone, the west-margin fault zone of Korea Peninsula and the south-margin fault zone of the Cheju Island jointly construct the boundary between the Sino-Korea and Yangtze blocks. Extending to the south end of the Korea peninsula, the Jiangshao fault zone appears as the boundary to separate the Yangtze and South China blocks. A clear difference in lithosphere structure exists for the continental shelf of the East China Sea and the Okinawa Trough. The former is similar to that in eastern China, belonging to an extension of the Eurasian continent; whereas the latter is a continent-ocean transition zone with a strongly thinned lithosphere. Along the Ryukyu-Taiwan subduction zone, the sinking of the Philippine Sea plate has a great effect on the upper mantle structures of the eastern China seas, while the interaction between the Eurasian continent and the Philippine Sea plate is a major reason for the thickening of the lithosphere of Taiwan area.

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