Polymer-bonded explosives (PBXs) are typical particulate composites of energetic crystals in a polymer matrix, which have a volume fraction of 60% to 95%. They are engineered to provide reliable performance and maximum safety envelopes through reduction of their sensitivity. There are three kinds of polymer-bonded explosive materials; namely, PBX1, PBX2, and PBX3. The last two polymer-bonded explosives were recently invented, in search of the more insensitive polymer-bonded explosive but with high detonation energy also. To investigate the dynamic response of new materials, the uniaxial compressive stress-strain behavior of the three polymer-bonded explosives was investigated as a function of temperature and strain rate. Constant and non-constant strain rate loading experiments were conducted in the use of pulse shapers. By comparing two different loads, the strain rate effect of these materials was found to depend on the instantaneous strain rate. The variations in failure stress, and failure strain with temperature, strain rate, and material composition were examined. The dependence of compressive strength on temperature and strain rate can be attributed to the Young's modulus and fracture surface energy according to Griffith criteria for fracture. The axial splitting caused by brittle fracture for most conditions was also investigated. Another failure mode of PBX2 agreed with the Mohr's failure mode criterion. All results show that PBX2 has more stable mechanical behavior and higher detonation performance.
[a] 1Introduction TATB is ac ommonly used insensitive explosive with high energy.T he main characteristics of TATB are its relatively low mechanical sensitivity and thermals ensitivity,a nd it is also safe and stable. In its actuala pplication, ap olymer binder in ac ertain proportion is often added to TATB, and then it can be compressed to ap olymer-bonded explosive (PBX) under high temperature and high pressure conditions. WhenP BX is compressed, the TATB granules undergo friction, extrusion, and propagation of pressure, thus affecting the microstructure and internal stress distribution of the compression molding [1,2].T he granule microstructure comprises the size, shape, and surface feature of the granules, connectionb etween the granules, the permutation and combinationo ft he granules,q uantitative relationship, and the distance between the granules, pore size, and distribution characteristics.T hesem icrostructuresa re important factors to confirm the physical, mechanics, and other characteristics of the explosivea nd will directly affect the density distribution and stress concentration of PBX,t hus affecting the safety performance and usability of the explosive. To investigatet he relationship betweent he changes in the microstructure causedb yc ompression and macroperformance, the various characteristics of microstructure should be accuratelye valuated. Electronm icroscope, matchingr efractive microscope, and polarizing microscope, etc. have beenu sed to achieve this objective [3][4][5][6][7][8][9][10][11][12][13][14].T hese methods cannot be used to observe the evolution of the internal structure,a nd some of them may cause secondary damage. With the development of controlt echnology and computer technology,X -ray computed tomography has been used to study and monitor the microstructure of explosives. Zhang et al.[15] studiedt he feature of RDX crystals under different pressures by mCT and discussed the issues including the displacement and breakage of the crystals, as well as the compressed density and distribution, gap filling, and microcrack distribution. They also obtained the completet hree-dimensional (3D) information of the microstructure of explosivew ith TATB radicals by moldp ressing at one-wayt emperature by CT [16].L an et al. [17], studied the microcosmic distributiono ft he internal crack of explosive and the healing statusbefore and after the disposal by the warm-pressing agingt reatment by CT.T ian et al. [18] observed the solidificationo fe xplosivea nd analyzed the distribution of internal thermal stress duringt he solidification. The above studies mainly evaluated the characteristics of explosiveb efore and after molding.C ombined the advantageso fC Tt echnology and the results of the studies on 3D systems, dynamico nline testing is also needed to study the characteristics of granules during the compression,i ncluding the morphological characteristicso f Abstract:I nt his study, an oninvasive experimental method and ad iscrete element method (DEM) model were used to investigate t...
Precise measurement of the inner structural strain of polymer bonded explosive (PBXs) granules during compression molding is highly desirable in order to investigate the inner stress distribution field and its underlying generation mechanism, with the aim of improving the stress distribution uniformity. In this contribution, TATB-based (1,3,5-triamino-2,4,6-trinitrobenzene) PBX granules were formulated and the stress-strain state of the PBX granules during the warm molding process was analyzed. Strain markers were implanted at different locations and the deformation characteristics and regularity of the embedded spherical strain markers were obtained by X-ray micro-tomography. Thus the local strain states at different locations could be obtained, and the local stress state could be deduced. The results showed that axisymmetric deformation occurred in all of the strain markers, where the flat strain ellipsoids were mainly compressed uni-axially. In the central region, the stress was mainly in an axial direction, and the shear force was small. Not only axial stresses, but also large shear stresses in the surrounding region of the cylindrical grains were present. The stress gradient in the central region was greater than that in the surrounding region. The stress was greater in the surrounding region because this region was squeezed by the mold. The maximum strain degree was 44.8% larger than the minimum strain degree. The local stress increment in each region was quantified. The stress increments of the three axes were in the range 14.2-19.5 MPa. This study examined the feasibility of evaluating the inner stress-strain state of PBX granules in a quantitative manner, which is significant in determining the inner strain and stress distribution in PBX granules during the molding process.
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