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Title: Anisotropy in the Ratchet Growth of PBX 9502

Abstract

TATB-based compactions and composites are known to undergo “ratchet growth”, an irreversible volume increase that occurs upon heating or cooling of a specimen. Ratchet growth likely arises because the coefficient of thermal expansion of the TATB crystals is strongly anisotropic, but the exact mechanism is not well-understood. TATB crystals in solid, plastic-bonded, explosive PBX 9502 parts can have a preferred crystallographic orientation (texture) caused by the compaction process. As a result, the irreversible strain associated with PBX 9502 ratchet growth is anisotropic. The present paper relates the magnitude of ratchet growth to the crystalline anisotropy of the TATB crystals. The crystalline anisotropy is measured by x-ray diffraction and the ratchet growth is measured by a digital image-correlation technique.

Authors:
 [1];  [1];  [1]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1172867
Report Number(s):
LA-UR-15-21827
DOE Contract Number:
AC52-06NA25396
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 36 MATERIALS SCIENCE; Crystallographic Texture; Explosive; PBX 9502; TATB; Ratchet Growth

Citation Formats

Schwarz, Ricardo Blum, Liu, Cheng, and Thompson, Darla Graff. Anisotropy in the Ratchet Growth of PBX 9502. United States: N. p., 2015. Web. doi:10.2172/1172867.
Schwarz, Ricardo Blum, Liu, Cheng, & Thompson, Darla Graff. Anisotropy in the Ratchet Growth of PBX 9502. United States. doi:10.2172/1172867.
Schwarz, Ricardo Blum, Liu, Cheng, and Thompson, Darla Graff. Thu . "Anisotropy in the Ratchet Growth of PBX 9502". United States. doi:10.2172/1172867. https://www.osti.gov/servlets/purl/1172867.
@article{osti_1172867,
title = {Anisotropy in the Ratchet Growth of PBX 9502},
author = {Schwarz, Ricardo Blum and Liu, Cheng and Thompson, Darla Graff},
abstractNote = {TATB-based compactions and composites are known to undergo “ratchet growth”, an irreversible volume increase that occurs upon heating or cooling of a specimen. Ratchet growth likely arises because the coefficient of thermal expansion of the TATB crystals is strongly anisotropic, but the exact mechanism is not well-understood. TATB crystals in solid, plastic-bonded, explosive PBX 9502 parts can have a preferred crystallographic orientation (texture) caused by the compaction process. As a result, the irreversible strain associated with PBX 9502 ratchet growth is anisotropic. The present paper relates the magnitude of ratchet growth to the crystalline anisotropy of the TATB crystals. The crystalline anisotropy is measured by x-ray diffraction and the ratchet growth is measured by a digital image-correlation technique.},
doi = {10.2172/1172867},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Mar 12 00:00:00 EDT 2015},
month = {Thu Mar 12 00:00:00 EDT 2015}
}

Technical Report:

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  • PBX 9502 is a plastic-bonded high explosive (PBX) containing 95 weight% TATB (triaminotrinitrobenzene) crystals in a polymer binder. TATB crystals are graphitic in nature, with a sheet-like structure and anisotropic CTE. Although the mechanism is not understood, solid-pressed TATB composites have been observed to undergo irreversible volume change ('ratchet growth') upon thermal cycling . This phenomenon has been studied but many aspects remain elusive and uncharacterized. Engineering or performance changes associated with ratchet growth have often been attributed to changes in density alone. We propose that the density changes which accompany ratchet growth involve a unique form of micro-damage distinguishablemore » from the pore structure associated with low-pressed density. We have performed ratchet growth studies on Recycled PBX 9502 between -54 to 80{sup o}C with density changes of about 1.5%. Specimens of the same density were obtained using a lower pressure in the manufacturing process. Comparative measurements were made using quasi-static uniaxial tension tests, as well as micro x-ray computed tomography and ultra-small angle neutron scattering experiments. Through these measurements we have shown that ratchet grown PBX 9502 has properties quite different from predictions based on density alone. The pore size distribution of ratchet grown specimens is unique and easily distinguished from parts pressed to an equivalent density.« less
  • A Netzsch dilatometer has been used to probe the ratchet growth response of TATB-containing PBX 9502. Preliminary data are presented, showing test reproducibility and examining possible effects of density and/or the specific sequencing of different thermal ranges. We have also shown effects of thermal ramp rate on the test data, likely due to thermal equilibrium of the specimen environment.
  • Pressed composites of TATB (2,4,6-trinintro-1,3,5-benzenetriamine) undergo irreversible volume change when subjected to thermal cycling. Using micro x-ray computed tomography and ultra-small angle neutron scattering, we have characterized the micro-structure of as-pressed and ratchet grown specimens of PBX 9502, a TATB-based composite, thereby distinguishing the effects of ratchet growth from the effects of density alone. Porosity differences are shown to effect mechanical properties, presented here, with ongoing efforts to evaluate sensitivity and/or performance effects.