Abstract
Placement and orientation of fasteners in assemblies is generally based on convenience or static load and strength considerations. Vibration and other dynamic loads can result in loosening of threaded product, particularly when cyclic shear stresses are present. This paper investigates the placement of a bolt and nut on a compound cantilever beam subjected to dynamic inertial loading. Calculations for an inertial loaded, cantilever, Euler-Bernoulli beam show that the dynamic shear stress is maximum near the dynamic nodal lines, and essentially vanishes near the anti-nodes. Experiments with a compound cantilever beam assembly with one fastener reveal that loosening occurs more readily when the bolt and nut are placed near a nodal line. Data presented include time to loosen, break-away torque, and acceleration level. The data shows that fastener integrity is maintained for longer periods of time and with lower tightening torques, when the bolt and nut are positioned away from nodal lines where shear stresses are lower, even though acceleration levels are higher.
