In-flight Conductivity and Temperature Measurements of Hypervelocity Projectiles

The conductivity and temperature of hypervelocity projectiles were studied using a novel magnetic diffusion analysis technique and five color radiometry. A copper shaped charge jet was fired through an electromagnetic coil to saturate the tip with a magnetic field. After leaving the coil, the tip passed through a series of sensing coils that are used to detect the magnetic field's decay rate, which depends on the geometry of the tip and its electrical conductivity. A mathematical model was then used to calculate the decay rate of the magnetic field from the tip and the signals produced by the sensing coils to determine the electrical conductivity. The resulting conductivity indicated that the tip of the shaped charge jet has a bulk temperature on the order of 1200 K. The experimental data were directly compared to temperature distributions generated by hydrocodes using both the Johnson-Cook and Steinberg-Guinan-Lund strength models. Because the magnetic diffusion technique is extremely versatile, various projectiles over a broad dynamic range can be investigated. Thus, this measurement is compared to radiometry and diffusion measurements of explosively formed penetrators.