Nonlinearity in the piezoresistance coefficient of impact-loaded manganin

Abstract

The piezoresistance response of shock-loaded manganin wire embedded in C-7 epoxy insulation was experimentally determined over the stress range from 4 to 94 kbar. Manganin stress gauges of this configuration have been used extensively in previous shock wave studies. Interpretation of shock profiles below 50 kbar has been hampered, however, because the relationship between change in resistance and shock stress was not well established. The results of this work show the manganin piezoresistance coefficient to be nonlinear in the low-stress region, varying from 0.00246 Ω/Ω kbar at 9 kbar to 0.00291 Ω/Ω kbar at 40 kbar. Good agreement was observed between the shock and hydrostatic coefficients up to 9 kbar; the piezoresistance data above 40 kbar agreed with previously published high-stress results. The nonlinear increase in the manganin piezoresistance is attributed to defects generated in the wire by plastic deformation accompanying the shock loading. The stress-particle velocity response of the C-7 epoxy used in the stress gauge was also characterized, with Hugoniot and release adiabat data being generated. The epoxy Hugoniot data were significantly different from previously reported data for stresses below 20 kbar.