A Thermal and Nanomechanical Study of Molecular Crystals as Versatile Mocks for Pentaerythritol Tetranitrate

Abstract

Pentaerythritol tetranitrate (PETN) is a commonly used high explosive (HE) in detonators. Often, surrogate or “mock” materials are used in place of HE for mechanical tests, proofing out equipment, or developing new diagnostics. However, there is no commonly accepted mock for PETN. A good mock should match at least one physical property of the target material, and ideally mimic multiple thermal and mechanical properties. Here, we investigate several molecular crystals to evaluate their efficacy in mocking PETN density, melting point, elastic modulus, hardness, plastic deformation, and fracture behavior. Materials were tested with a combination of calorimetry and nanoindentation. Two materials, 2,4,6-trifluorobenzoic acid (246 TFBA) and mesoerythritol, were downselected for detailed indentation study after the initial round of screening experiments, both were found to mimic PETN mechanical behavior quite well, 246 TFBA closer to PETN in most properties (hardness, modulus, and density) than erythritol, but erythritol having advantages in relative cost and matching the onset of yield. Depending on the desired implementation of the mock, one material may be preferred over the other, but both have potential as generic mocks for PETN. Nanoindentation is demonstrated as a versatile tool to provide rapid screening of these materials’ mechanical properties.

High-Fidelity Mock Development for the Insensitive High Explosive TATB

“…Nanoindentation was performed using a Hysitron Triboindenter 950 with a Berkovich indenter probe. Loading profiles were quasi-static open loop with 30 s loading, 5 s hold, and 5 s unloading, chosen to resemble prior indentation studies [12,17,19], with peak loads chosen for each material so as to not exceed an indentation depth of 250 nm; this peak load was 300 µN for hexamine, 500 µN for IAA, 1000 µN for melamine, and 1000 µN for TTDO. To determine hardness and elastic modulus, the Oliver and Pharr method [34] was used, for which 7 indents were performed on hexamine, 8 on IAA, 10 on melamine, and 5 on TTDO.…”

“…The methodology used here to generate a list of mock candidates and choose a selection of those materials for further testing has previously been reported for HMX and PETN [9,12]. Eleven materials were initially chosen as potential mock candidates for TATB: ammelide, ammeline, AOCA, BBA, BTFAP, hexamine, IAA, ISA, melaine, PFPAP, and TTDO.…”

“…These type of high fidelity mock materials will replicate the most important physical parameters of an explosive, such as density, while approximating as many other thermal and mechanical properties of the parent PBX as possible. Our methodology of identifying new potential mock crystals has been detailed in a previous publication where HMX was the target, and we will employ similar methodology here for TATB [12]. Literature methods for selecting mock candidate materials fall into two general themes: (1) select an organic molecular crystal with similar chemical structure to the HE of interest [13][14][15]; or (2) identify inert materials which mimic a specific property of interest, and then select a candidate that most closely matches other secondary properties of interest [6,8,16].…”

“…The accuracy, repeatability, and small sample quantity need for nanoindentation make it an ideal test for HE crystalline materials, where the explosive hazard is directly correlated to the amount of sample being tested or handled during an operation. Nanoindentation has been previously used to determine the mechanical properties of many explosive crystals such as HMX, RDX, TATB, pentaerythritol tetranitrate (PETN), and others [12,[17][18][19][20][21]. In addition to a candidate material's mechanical properties, the crystals must be able to be grown to a specific size range to best allow for mimicking the PBX microstructure in a mock composite system.…”

Compressive strength of the plastic-bonded explosive surrogate idoxuridine under quasistatic and dynamic compression

“…[18][19][20][21][22][23] In recent years, there has been increased interest in developing high fidelity mock materials, such that a single inert material can be used to simulate several properties of its explosive counterpart rather than just one or two. 24,25 For cyclotetramethylene-tetranitramine (HMX), the explosive component of PBX 9501, there has been success with the pharmaceutical material 5-iodo-2 0 deoxyuridine (idoxuridine or IDOX) under various thermal and mechanical test conditions. [26][27][28][29][30] IDOX is preferable to former mocks such as sugar mock PBS 9501 due to improved performance relative to HMX in thermal environments, closer density match to HMX, and ease of formulating plastic-bonded composites.…”