Abstract
Recently, wheel separation accidents in such vehicles as trucks, buses and passenger cars have drawn a social concern. Explications of their causes and adequate practices of countermeasures for them have been urgently required. As main causes of wheel separation of a large-sized car, two reasons, "over-tension of wheel nuts from excessive fixing torque" and "over-loading of cargos", are pointed out. The phenomenon which a bearing surface expands radially by the plastic deformation of a fastened body depended with over-tension is a problem peculiar to a nut with spherical-form bearing surface or a taper nut. This report deals with this subject about a nut with a spherical bearing surface. In this report, the tightening experiment with spherical bearing-surface wheel nut was conducted. As the result, the characteristic about the torque of a spherical bearing-surface wheel nut was observed, and the stress near the bearing surface when tightening was measured.
