As self-loosening of nuts is really a problem for bolted joints in practical use, countermeasures for the loosening is highly required. In this situation non-loosening fasteners are one of the resolutions for any fastened machinery as an essential mechanical element. Self-loosening of threaded bolt/nut systems has been researched in number of works and many of them were based on experiments historically and some were based on the finite element analyses in these years. Authors have reported the static loosening of nut due to the transverse motion of fastened objects in PVP conferences using finite element analyses and showed the loosening mechanism. This paper will show another case based on the dynamic situation namely impacting of the bolt/nut systems as NAS3350/3354 test situation. In this special case, nut loosening was reproduced, too, and it shows that the loosening mechanism is almost the same as the static loosening, although the loading is quite different. Even in impact condition, the analysis showed that the effect of eccentric nut works to prevent self-loosening.

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