Phenomenological modeling of imperfect electric contacts using a three-dimensional finite element model

The nature of the physical and electrical phenomena associated with an imperfect electric contact (ImPEC) is an important aspect of the operation of electromagnetic launchers and other high power electromechanical systems. A better understanding of these phenomena and the ability to model them are indispensible if advancements in the state of the art are to be achieved. This study deals with two of the phenomena that have significant influence on the behavior of the contact interface whether the contacting members are stationary or sliding. These are the behavior of the electric currents as they diffuse into the contacting members, and the generation and subsequent diffusion of heat generated by these currents.;To study the electric diffusion effect, a numerical study is performed for a pair of conducting bars in contact with each other at a number of rectangular shaped contact spots. For the thermal effect, contact-area-resistance and a surface heat flux source are introduced at the contact interface to facilitate the modeling of the heat generated in the imperfect electric contact region. The dependence of the contact-area-resistance is investigated and incorporated into an analytical model used for numerical simulation. Two physical experiments are performed on stationary contacting members to establish experimental values for the ImPEC model and to sample the temperature variations in the contacting members caused by the passage of DC across the contact. These results are compared to those obtained from the simulations and reasonable agreement was observed. The properties of the interface obtained from both the simulation and experimental studies are incorporated into two numerical simulations using the EM FE code EMAP3D. The simulation of melting over the armature contact interface for the Eglin railgun experiment was compared with melting observed in the recovered armature. It is reasonable to conclude that the melting map of the simulation results correlates with that of the experimental result, and that the ImPEC effect dominates at the early launching stage.