Design of a Precision Tribo-Tester for Studying Contact Transitions

The successful operation of an electromagnetic launcher (EML) and its life are dictated by the nature of the electrical contact between the armature and the rail. Several numerical and finite element models have been developed to understand some aspects of physics of the events happening at the sliding interface but a lack of precision test bed for such measurements inhibits validation of several theories. A precision bench-top tribo-tester has been developed to simulate the critical operating conditions in an EML chiefly contact pressure ~250 MPa and current densities ~10 GA/sq.m. The tester consists of a linear servo motor translating a pin on a 2 meter long flat surface. The electrical current to the interface is supplied by a programmable 8V/350A power supply while the loading of the pin against the flat surface is provided by means of a pressure controlled pneumatic actuator. The normal force and the friction force at the interface, temperature of the rail surface, current and voltage drop across the interface and position are monitored during the course of sliding. The tester offers flexibility in terms of testing different contact geometries and materials under various operating conditions. The test measurements explain the evolution of the friction force, electrical resistance and the temperature rise of the interface during the course of sliding. The measurements would be used to determine correct surface geometry and material combination(s) to achieve a good electrical sliding contact with low wear in EML's.