Electromagnetically Driven Expanding Ring With Preheating

Experiments were conducted that simulate the time-varying mechanical and thermal conditions typically found in electromagnetic launchers. While materials that are slowly heated isothermally have adequate time for fundamental microstructural changes that weaken them to occur, the mechanical strength of metals subjected to rapidly varying high-temperature pulses is dependent on heating rate and duration. Previous work has shown that tabulated properties of high-temperature materials inadequately describe such materials under pulsed heating conditions. In this paper, electrolytic tough pitch copper ring samples have been heated to a peak temperature in the range of 450 degrees C over about 25 ms. The samples are first inductively preheated with low current before using a short-duration high-current pulse to expand the ring. A new photonic Doppler velocimetry system was used to accurately measure the velocity profile during the dynamic thermal and mechanical conditions. Preheating the specimens to 200 degrees C resulted in a 30% drop in strength when compared to samples without preheating.