Parametric study of threaded fastener loosening due to cyclic transverse loads

This paper presents results from an experimental investigation of mechanical loosening in bolted joints due to cyclic transverse loads. The influence on the resistance to loosening of basic parameters such as preload, fastener material elastic modulus, nominal diameter, thread pitch, hole fit and lubrication is quantified. Sixty-four tests have been performed as part of a nested-factorial design in which the nominal diameter is the nesting factor of preload, thread pitch and hole fit. A statistical analysis identifies the factors and interactions that significantly affect the resistance to loosening and it is found that the preload and the fastener elasticity are the most influencing parameters. A statistical model is developed that predicts the level of loosening reached by a threaded fastener under defined conditions. The analysis shows that optimum conditions to avoid fastener loosening are high preload, low modulus of elasticity, large diameter, lubrication, tight fit and fine threads.