Loosening of bolted joints by small plastic deformations
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Formulas are derived for several cases of loosening of bolted joints caused by stresses in excess of elastic limits and accompanying permanent deformations. It is shown that loosening occurs during the initial application of an external force, but that subsequent repetitions of the same force cause no further loosening. External impact loads, which require a definite energy absorption of the joint, result in loosening upon both the initial load application and later repetitions. The effects of initial tightening, gaskets, and spring washers are investigated. Loosening under moderate loads may be completely avoided if the initial bolt tension does not exceed a certain maximum value. Loosening is unavoidable under extremely high loads, but the amount of loosening can be decreased by use of higher initial tensions. Illustrative experimental data are reported .