SUMMARY

The interface of the sliding armature and the stationary rail in an Electromagnetic launcher (EML) is subjected to high contact pressures and extremely high current densities. The behavior of the interface has a direct bearing on the overall performance and the efficiency of the EML. Joule heat generated at the interface can lead to the melting of the interface ensuing in the loss of the electrical contact between the armature and the rail. Identifying and controlling the key factors that lead to contact melting has the potential of improving the efficiency of the launch process. To investigate the behavior of the interface under the extreme conditions of high contact pressures (30 MPa – 500 MPa) and large current densities (100 MA/m2 to 20 GA/m2) an experimental test bed has been built. A multi-scale contact resistance model is developed to predict the real area of contact and the electrical contact resistance under static conditions. A new methodology to evaluate the heat partition between two bodies in contact is presented. From the predicted real area of contact, electrical contact resistance and heat partition between the two bodies, the time required to initiate melting at the interface will be evaluated. Effect of other factors like surface roughness, surface texturing and lubricants can be easily studied on the test bed to achieve controlled interface melting. Microstructure evaluation and micro-hardness measurements will be conducted to gain better understanding of the interface temperature. The significant contributions of the work are: (i) A new methodology to calculate heat partition and temperature rise at the interface of two sliding bodies, (ii) A multi-scale model for estimating electrical contact resistance, (iii) a predictive model for interface melting with experimental validation, and (iv) a wealth of experimental data regarding the role of current density, load and speed on friction coefficient, electrical contact resistance and wear rate.