Self–threading bolts tapped into temperature–dependent plastic bosses

The effects of mechanical and thermal loads on metallic bolt– fastened plastic joints in automotive interior trims were analysed using nonlinear finite element methods and statistical design of experiments. Temperature dependent constitutive models were considered to investigate the potential failure of plastic bosses, being fastened by self–tapping double–threaded bolts with different thread heights. A high compressive stress at the inside diameter of the moulded hole in the plastic boss can be produced after the tapping and fastening process is completed, when the hole size is big. The compressive stress may result in the loss of fastening force, when the bolted–joint is subjected to an elevated temperature. Bolt pitch length, bolt thread angle, and inside diameter of the moulded hole are shown to have significant influence on the von Mises effective stress which is used as the failure criterion.