Modeling and simulation of sparking in fastening assemblies

This paper deals with modeling and simulation of sparking occurrence in fastening assemblies. The principle consists to calculate in three dimensions the distributions of current density and temperature in the structure over time, and to derive some physical criteria to estimate the possibility of sparking occurrence. Simulations are performed with a Finite Volume Method in time domain and an unstructured mesh. Low frequency assumption is considered for the calculations of electromagnetic quantities (quasi static assumption). The contact resistances between each elements of the structure are also considered, assuming a uniform distribution of the resistance on the interfaces. The two main mechanisms involved in the not-linear behavior of the fastener during high current components are also modeled. First, dielectric breakdowns of sealant layers are simulated with their dielectric strength. Two different situations are simulated. In the case of a direct attachment of the lighting arc on the fastener, the current enters the assembly through the bolt. In the case of conduction, the current (fraction of D component) passes from the skin to the rib through the bolt. The results of simulations bring to light the role of the contact resistances between the bolt and other elements (rib, skin, nut...) on the occurrence of sparking. In some case, computations indicate some important reinforcements of the current density of more than 10kA/mm2, resulting to a strong local heating of the bolt and a possible sparking occurrence.