RIA: Dynamic Loosening and Tightening of Threaded Fasteners by Vibration

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Threaded fasteners have found ubiquitous use in many systems and structures. Although frequently overlooked, fasteners represent a complex and often critical design element. To some extent, all fasteners are subjected to unsteady loading. Yet the behavior of threaded fasteners under such conditions is still poorly understood. Existing analyses of threaded fasteners under vibration are based on static equilibrium conditions with supporting data limited to only low-frequency conditions. Such analyses suggest that only a net loosening action can occur. However, preliminary experiments show that when a broad range of vibratory conditions are considered, alternate ranges of frequencies are found in which either a loosening or a tightening action occurs. The goals of this research are to perform well- controlled measurements of the dynamic forces and motions of threaded fasteners under a wide range of dynamic conditions and to develop appropriate nonlinear dynamic models of threaded fasteners which capture and explain the dynamic loosening and tightening motions. The models will accommodate the interaction of friction and vibration as well as the dynamic constraints and nonlinearities inherent to threaded components. The results of the work are expected to be of fundamental engineering interest and have immediate use in the design of joints in many critical applications.***//