Self-loosening of nuts is a practical problem in any situations from a single machine to a whole plant. Self-loosening of threaded bolt/nut systems has been researched in number of works for a long time and many of them were based on experiment historically. Some works based on finite element analysis are increasing in these years. Authors have reported the static loosening of nut due to the lateral motion and dynamic loosening due to the lateral impact of fastened objects in PVP conferences using finite element analyses, and showed the loosening mechanism. This paper is a continuing research work and shows another loosening case due to the thermal load to bolt/nut system. It is observed that the bolt and nut are loosened, if they are subject to temperature difference. In this paper, nut loosening was reproduced in the finite element simulations. Self loosening mechanism of this phenomenon is discussed.

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