Dynamic Mechanical Behavior of PBX

Abstract

1IntroductionPolymer bonded explosives (PBXs) [1][2][3][4] have usually been considered as ap articulate composite material containing the energetic materials hexahydro-1,3,5-trinitro-1,3,5-s-triazine (RDX) embedded in av iscoelastic polymer binder. PBXs are widely used in av ariety of conventional engineering and aerospace fields. As ah ighly-filled composite material, PBX exhibits complex physical and mechanical properties that are dependent on an umber of variables, such as temperature, strain rate, grains weight, and size distribution of grains, etc. [5,6].The Los Alamos National Laboratory (LANL) performed al ot of research on dynamic mechanical properties of PBXs. These results suggested that dynamic mechanical properties of PBX are strongly influenced by strain rate and temperature [7][8][9][10].A lso, the compressive strength is enhanced when increasing strain rate or decreasing temperature. PBX9501i sw idely researched at present,a nd the result illustrated that PBX9501 duringh igh-rate loading continue straining after the maximum flows tress have been achieved. Figure 1s hows the published compressive stress-strain data on PBX9501 currently known to the authors. When the peak strengths of PBX9501 are achieved, the flow strength beginst od ecline sharply because of damage accumulation. Graye tal. [11] revealed that at high-rate PBX 9501 fails via predominantly transgranular cleavage through the HMX crystals. Strains to failure remain almost constant throughout,a talevel of approximately 1-3 %. In fact, these damagep rocesses give rise to the enhanced sensitivity of PBX9501 followinga ni mpact.In the presented work, the micromechanical modelh as profited greatly from the theoretical analysis of Weng and co-workers [12-17] and considerable referencet ot heir work is madet hroughout this article. Their work is based on Eshelby's celebrateds olution of the stressa nd strain fields arising from the presence of an ellipsoidal inhomogeneity in an elastic matrix and Mori and Ta naka'se ffective medium theory,w hich was used to extendE shelby's analysis to larger valueso ff iller concentration [18,19].C lements and Mas have put forth am ethod that is ah ybrid of two Abstract:T he dynamic mechanical properties of PBX1314 and its binder are systematicallyi nvestigated. Based on split-Hopkinson pressure bar technique, the experimental results of PBX1314 and its binder are obtainedu nder high strain rate. Ac onstitutive theory is developed for modeling the mechanical response of dynamically loaded PBX1314 binder.T oa ccomplish this aim, the PBX1314 binderi sa ssayed by relaxation tests at different temperatures, in order to apply the time-temperature superposition principle (TTSP) and raise the masterc urves, based on WLF equation.The rate dependence of mechanical response of the polymer binder is accounted for by ag eneralized Maxwell viscoelasticity model. The basis for this work is Mori and Ta naka's effectivem ediumt heory.T he grains in this analysis are assumed to be spherical and uniformly distributed in the b...

Dynamic Compressive Properties of Polymer Bonded Explosives under Confining Pressure

“…The essential idea in the TTSP method is the assumption that the monitored parameter values obtained at short times and high temperatures can be used to predict parameter values at long times and low temperatures [3,29]. In its simplest form this principle means that curves of E(t) or log E(t) versus log (t) that are obtained at different temperatures are superposable by means of a horizontal shift along the log (t) axis.…”

“…The diameter of the striker, incident and transmission bars is 20 mm, and the length of the incident and transmission bars is 1500 mm. In our work, the bars are made of aluminum, of which density and Young's modulus are 2.7 g/cm 3 and 73 GPa, respectively. In order to minimize the effects of friction on specimen-bar interfaces, a thin layer of high-purity petroleum jelly is applied between the specimen and the bar ends.…”

High speed X-ray phase contrast imaging of energetic composites under dynamic compression

“…The de-bonding between the energetic crystals and the binder was the main fracture mode observed in the quasistatic experiments. 14,21,22 As the loading rate was increased, the stiffness of the PBX samples increased 14,15,19 and higher number of crystals were observed to fracture. 14,15,23 The main fracture mechanism for the energetic crystals was the trans-granular fracture caused by the tensile stress generated due to particle-particle contacts.…”

“…The fracture behavior of the PBX specimens has also been studied with uniaxial compression, [13][14][15][16][17][18][19] nanoindentation, 20 and Brazilian experiments [21][22][23] at various strain rates. The de-bonding between the energetic crystals and the binder was the main fracture mode observed in the quasistatic experiments.…”

Investigating the static and dynamic tensile mechanical behaviour of polymer‐bonded explosives

“…Low‐strength and low‐impedance materials pose significant challenges in the design of experiments to determine dynamic stress–strain curves. In our previous work, the dynamic compressive properties of the PBX were studied using a modified split Hopkinson pressure bar (SHPB) experiment and a micromechanical model . It can be found that there are differences between uniaxial compression and tension in mechanical properties.…”