Pulsed Current Static Electrical Contact Experiment

• Published in: IEEE transactions on magnetics 2007-01, Vol.43 (1), p.343-348
• Main Authors: Jones, H.N., Neri, J.M., Boyer, C.N., Cooper, K.P., Meger, R.A.
• Format: Article
• Language: English
• Subjects: Acceleration; Applied sciences; Contact; Contact pressure; Contacts; Current density; Dissimilar metals; Electric contacts; Electric currents; Electric potential; electrical contacts; Electrical engineering. Electrical power engineering; Evolution; Exact sciences and technology; History; Magnetism; Mechanical factors; Miscellaneous; Projectiles; Pulsed current; railgun; Railguns; Temperature; Thermal force; Various equipment and components; Voltage
• ISSN: 0018-9464; 1941-0069
• DOI: 10.1109/TMAG.2006.887716

Railguns involve both static and sliding electrical contacts, which must transmit the large transient electrical currents necessary to impart high forces onto a projectile for acceleration to hypervelocity. Static electrical contacts between metals initially take place through small asperities, or "a-spots", distributed over the contact area. The voltage developed across the interface is directly related to the contact temperature and force, the number of a-spots, the thermophysical and mechanical properties of the contacting materials, the current history, and any interfacial materials that may be present. To physically simulate some of the conditions attained within a railgun, a pulsed current static electrical contact experimental facility has been developed at the Naval Research Laboratory. This facility employs a 500-kN capacity servohydraulic load frame equipped with an electrically insulated load train to establish a contact force on interfaces between metals through which a pulsed current is transmitted. The time dependent evolutions of the voltage drops across the interfaces, as detected by probes pushed into the contacting materials, are recorded during a 40-kA peak current pulse having a 300-mus rise time with peak current densities on the order of 50 kA/cm 2 . The interface stack is assembled from a 12-mm outside diameter annular disk of metal with a 6.3-mm hole which is compressed between two hollow pedestals of a second metal. The evolution of the voltage drop across an interface during a pulse will be described as a function of initial contact pressures, current density, and polarity for dissimilar (Al/Cu) metal contacts. Thermal effects on the surfaces, including localized melting of the interface materials, were also investigated