Characterization of thermally degraded energetic materials

Abstract

Characterization of the damage state of a thermally degraded energetic material (EM) is a critical first step in understanding and predicting cookoff behavior. Unfortunately, the chemical and mechanical responses of heated EMS are closely coupled, especially if the EM is confined. We have examined several EMS in small-scale experiments (typically 200 mg) heated in both constant-volume and constant-load configurations. Fixtures were designed to minimize free volume and to contain gas pressures to several thousand psi. We measured mechanical forces or displacements that correlated to thermal expansion, phase transitions, material creep and gas pressurization as functions of temperature and soak time. In addition to these real-time measurements, samples were recovered for postmortem examination, usually with scanning electron microscopy (SEM) and chemical analysis. We present results on EMS (HMX and TATB), with binders (e.g., PBX 9501, PBX 9502, LX-14) and propellants (AVAP/HTPB). DISCLAIMERThis rcporr was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof. nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any spccific commercial product, process, or senice by trade name, trademark, manufacturer, or otheiwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States G o m m e n t or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

Cookoff

“…PBX 9501 has a bimodal crystal size distribution centered approximately on 25 and 130 μm [18] and those samples that ignited later and hotter may have lacked large particles. The observation of DDT in such small samples supports other observations that both the material state and chemical kinetics are very different after prolonged periods at elevated temperature, and that these changes effectively reduce the insensitivity of the PBX [19][20][21].…”

LDRD final report : raman spectroscopic measurements to monitor the HMX beta-delta phase transition.

“…The load response agreed with previous experiments. 1,2,9,10 As shown in the load cell response, thermal expansion of the material occurred to the point just before the phase transition at approximately 150 °C, where a shrinkage of the material occurred, shown by a decrease in the load. This shrinkage has been documented by Herrmann et al 12 A sharp rise in the load was observed during the phase transition, in accordance with the lower density of the δ-phase.…”

“…1,2,9,10 The Raman hot cell apparatus, as seen in Figure 2, is similar to other hot cells with modifications to accommodate the Raman probe. It consists of a 6.35-mm diameter x 3.18-mm length (1/4 in.…”

Data Analysis, Pre-Ignition Assessment, and Post-Ignition Modeling of the Large-Scale Annular Cookoff Tests

“…The SNL confined cookoff hot-cell experiments (Renlund et al 1998) and the instrumented thermal ignition (SITI) experiments at lower temperatures (Kaneshige et al 2003) show lower levels of decomposition. SNL's hot-cell experiments indicate that when a confined PBX-9501 sample is heated to 190°C for 1 hour, there is no mass loss, and when the sample is heated to 200°C, the mass loss is 1% (Renlund et al 1998). The pressures recorded within the SITI confinement are consistent with a small mass fraction of explosive being decomposed.…”