The self-loosening process of a bolted joint consists of two distinct stages. The early stage of self-loosening is due to the cyclic plastic deformation of the materials. The second stage of self-loosening is characterized by the backing off of the nut. The current work is concentrated on an experimental investigation of the second stage self-loosening. Over one hundred bolted joints with M12×1.75 bolts and nuts were experimentally tested using a specially designed testing apparatus. The experiments mimicked two plates jointed by a bolt and a nut and were subjected to cyclic transverse shear loading. During an experiment, the relative displacement between the two clamped plates, denoted by δ, was a controlling parameter. For a given preload, the relationship between, Δδ/2, the amplitude of the relative displacement between the two clamped plates, and, the number of loading cycles to loosening followed a pattern similar to a fatigue curve. There existed an endurance limit below which self-loosening would not persist. A larger preload resulted in a larger endurance limit. However, a large preload increased the possibility for the bolt to fail in fatigue. The results suggest that the use of a regular nut is superior to the use of a flange nut in terms of self-loosening resistance.
An Experimental Study of Self-Loosening of Bolted Joints
Contributed by the Reliability, Stress Analysis, and Failure Prevention Committee for publication in the JOURNAL OF MECHANICAL DESIGN. Manuscript received September 2003; revised January 2004. Associate Editor: E. Sancaktar.
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Jiang , Y., Zhang, M., Park, T., and Lee, C. (October 28, 2004). "An Experimental Study of Self-Loosening of Bolted Joints ." ASME. J. Mech. Des. September 2004; 126(5): 925–931. https://doi.org/10.1115/1.1767814
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