Yuri A. Gruzdkov

Thermomechanical model and temperature measurements for shocked ammonium perchlorate single crystals

A consistent thermomechanical material model was developed for unreacted ammonium perchlorate (AP) single crystals for shock compression normal to the (210) and (001) crystal planes. Building on previous work, the mechanical response for both orientations was described using a single isotropic elastic-plastic model and an overstress model to describe rate-dependent yielding. Velocity interferometer measurements to 12 GPa were performed to extend the AP Hugoniot curve to higher stresses. The specific heat cv, the coefficient of thermal pressure (∂P/∂T)V, and the isothermal bulk modulus BT were determined from Hugoniot and isothermal compression curves, along with available data at atmospheric pressure. Time-resolved Raman spectroscopy experiments were carried out under stepwise loading to obtain temperatures in the shocked state. Calculated temperatures using our material model are in good agreement with the temperatures obtained from our experiments, thus providing validation for our modeling approach.

Spectroscopic Study of Shock-Induced Decomposition in Ammonium Perchlorate Single Crystals

Time-resolved Raman scattering measurements were performed on ammonium perchlorate (AP) single crystals under stepwise shock loading. For particular temperature and pressure conditions, the intensity of the Raman spectra in shocked AP decayed exponentially with time. This decay is attributed to shock-induced chemical decomposition in AP. A series of shock experiments, reaching peak stresses from 10-18 GPa, demonstrated that higher stresses inhibit decomposition while higher temperatures promote it. No orientation dependence was found when AP crystals were shocked normal to the (210) and (001) crystallographic planes. VISAR (velocity interferometer system for any reflector) particle velocity measurements and time-resolved optical extinction measurements carried out to verify these observations are consistent with the Raman data. The combined kinetic and spectroscopic results are consistent with a proton-transfer reaction as the first decomposition step in shocked AP.

Time-resolved absorption spectroscopy in shocked PETN single crystals

Extinction spectra of PETN and photodiode transmission records, with 50 and 0.5 ns resolution respectively, were obtained for shock compression along the [110] and [100] directions. Light extinction was found to be due to absorption; the contribution of scattering was measured to be below 0.001%. Results for final stresses up to 10 GPa (stepwise loading) and initial stresses up to 5 GPa are presented. Broad band absorption in the visible appeared in PETN single crystals shocked to as low as 1 GPa. Absorption changes were measured as a function of time, stress, and crystal orientation. The process responsible for absorption occurred on a time scale faster than 0.5 ns. Work is in progress to identify the origin of the absorption.

Equation of state and temperature measurements for shocked ammonium perchlorate

A thermodynamically consistent equation of state (EOS) was developed for unreacted, single-crystal ammonium perchlorate (AP) for shock compression along the [210] and [001] directions. The specific heat, cv, the pressure-temperature coefficient, (∂P/∂T)v, and the isothermal bulk modulus, BT, were determined from Hugoniot and isothermal compression curves, along with available data at atmospheric pressure. The mechanical response of each orientation of the AP crystal was modeled as an isotropic elastic-plastic solid. Above the HEL, the rate dependent yielding of AP was described with a simple overstress model. Time-resolved Raman spectroscopy experiments were carried out to obtain temperatures in the shocked state. These temperature measurements were used to constrain the values of various EOS parameters.

Time-resolved emission spectroscopy in shocked PETN single crystals

Time-resolved emission spectroscopy was used to probe molecular changes in pentaerythritol tetranitrate (PETN) single crystals shocked along the [100] and [110] orientations. Temporal and spectral characteristics of emission were determined in thin crystals subjected to stepwise loading to 10 GPa. The emission data were analyzed in conjunction with absorption measurements performed under the same loading conditions. The temporal and spectral features of the emission were found to be dependent on both the final stress and crystal orientation. In addition, the spectra change with time and display the presence of two components. Possible origin of the observed light emission is discussed briefly.