Eric S. Martin

Second-harmonic generation and the shock sensitivity of TATB

The recent discovery of significant differences in second-harmonic generation (SHG) from various grades of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) prompted an investigation into the sensitivity of TATB based upon the crystal structure and morphology as indicated by SHG intensity. The Floret test was used as a means for rank ordering the shock sensitivity properties of fine TATB samples. Two types of TATB, which showed low SHG and performed poorly, were heated to obtain a much higher level of SHG, and then tested to compare sensitivities. One of the samples was significantly desensitized, and the sensitivity of the other was unchanged. Interpretations are presented which attempt to explain the relationship of SHG to the shock sensitivity of TATB. Although particle size and pressing density appear to be the main drivers for shock sensitivity, SHG intensity evaluations may help explain departures from those trends.

Measurements of the DDT Process in Exploding Bridgewire Detonators

The deflagration‐to‐detonation transition (DDT) of low density (0.88 g/cc) PETN during exploding bridgewire (EBW) initiation has been studied using laser interferometry and streak photography. Cutback experiments using VISAR have confirmed a 1.0 mm run‐distance to detonation in this low density PETN powder. In a detonation system using a combination of low and high density powders, an apparent center of initiation (COI) analysis of streak data has yielded a surprisingly similar result. This data suggested that a compaction of low density powder to near theoretical maximum density (TMD) may occur before the onset of detonation, which is consistent with work done previously. These experiments show this is not the case and COI analysis reveals a non‐ideal initial propagation front. Additionally, data show that although function time increases significantly with decreasing firing voltage, the apparent COI changes very little. This indicates that the detonation criterion is not dependent upon the rate of deflagration, but on a volume of material that must be burned in a confined space to create the critical pressure needed at the compaction front.

On the Initiation Mechanism in Exploding Bridgewire and Laser Detonators

Since its invention by Los Alamos during the Manhattan Project era the exploding bridgewire detonator (EBW) has seen tremendous use and study. Recent development of a laser‐powered device with detonation properties similar to an EBW is reviving interest in the basic physics of the deflagration‐to‐detonation (DDT) process in both of these devices. Cutback experiments using both laser interferometry and streak camera observations are providing new insight into the initiation mechanism in EBWs. These measurements are being correlated to a DDT model of compaction to detonation and shock to detonation developed previously by Xu and Stewart. The DDT model is incorporated into a high‐resolution, multi‐material model code for simulating the complete process. Model formulation and the modeling issues required to describe the test data will be discussed.

Instrumented Floret Tests of Detonation Spreading

The floret test was originally devised to permit comparison of detonation‐spreading performance of various insensitive explosive materials, using only the dent in a copper witness plate as a metric. Dent depth in the copper plate is directly related to the fraction of a thin acceptor pellet that was detonated by impact of a small explosive‐driven flyer plate. We have now added instrumentation to quantitatively measure the detonation corner‐turning behavior of IHEs. Results of multi‐fiber optical probe measurements are shown for LLM‐105 and UF‐TATB explosive materials. Results are interpreted and compared with predictions from one reaction‐rate model used to describe detonation spreading, and may be advantageous for comparison with other reactive‐flow wave‐code models. Detonation spreading in UF‐TATB occurred with formation of a non‐detonating region surrounding a detonating core, and re‐establishment of detonation in a “lateral” direction beyond that region.

Preparation and Characterization of Fine‐Particle NTO and Its Formulation with Al Nanopowders

We have initiated study of the effect of nano‐aluminum on the detonation performance of NTO. A novel method for the preparation of both fine‐particle NTO (UF‐NTO) and its formulation with Al nanopowder has been developed. Results from small‐scale sensitivity tests on both the UF‐NTO and aluminized NTO composite indicated that they are insensitive to impact, friction and HESD. The performance of both UF‐NTO and NTO/Al mix was evaluated by detonation‐spreading floret tests. At the same pressed density, it was found that, when initiated by a 3‐mm‐diameter flyer plate, the aluminized NTO composite produced a shallower dent on a copper witness plate than neat UF‐NTO and thus was inferior to UF‐NTO in detonation spreading.

Transient Detonation Processes in a Plastic Bonded Explosive

Experiments involving the transfer of detonation from small booster charges of PBXN‐5 (95% HMX and 5% Viton A) into larger charges of various plastic‐bonded explosives (PBXs) have produced some surprising results and have stimulated investigation into the factors governing observed responses. To understand these results, we conducted a series of tests with different miniature detonator‐booster configurations using laser velocimetry to quantify the pressure pulse that is transmitted from the PBXN‐5 booster. Models were used to determine the ideal explosive behavior for comparison with the measured results. The differences are interpreted as being due to transient behavior and late‐time energy release from the booster charge. We characterize these behaviors as evidence of microdetonics, where we define microdetonics as the study of less‐than‐CJ detonation performance due to curvature and/or transient behavior. This provides useful insights into the fundamentals of the detonation process that can feed into advanced modeling approaches such as Detonation Shock Dynamics (DSD).Experiments involving the transfer of detonation from small booster charges of PBXN‐5 (95% HMX and 5% Viton A) into larger charges of various plastic‐bonded explosives (PBXs) have produced some surprising results and have stimulated investigation into the factors governing observed responses. To understand these results, we conducted a series of tests with different miniature detonator‐booster configurations using laser velocimetry to quantify the pressure pulse that is transmitted from the PBXN‐5 booster. Models were used to determine the ideal explosive behavior for comparison with the measured results. The differences are interpreted as being due to transient behavior and late‐time energy release from the booster charge. We characterize these behaviors as evidence of microdetonics, where we define microdetonics as the study of less‐than‐CJ detonation performance due to curvature and/or transient behavior. This provides useful insights into the fundamentals of the detonation process that can feed into a...