Effects of Friction Coefficient and Various Geometric Parameters on Loosening Phenomena of Bolted Joints under Shear Loads

Abstract

There are two types of loosening phenomena of threaded fasteners which sometimes cause serious accidents involving a variety of machines, structures and electronic devices: rotational loosening and non-rotational loosening of threaded fasteners. The former pattern frequently occurs due to shear loads repeatedly applied perpendicular to the bolt axis. This paper aims to clarify quantitatively how friction coefficients at contact surfaces and the geometry of threaded fasteners affect rotational loosening by conducting three-dimensional finite element analyses with the use of helical thread models. Numerical results showed that friction coefficient at nut bearing surface largely influences the loosening process, and that the introduction of fine screw threads and longer grip length are effective in preventing or mitigating the progress of thread loosening. Based on the foregoing results, a practical proposal is made for the prevention of thread loosening.