We develop strain-driven compression-expansion technique using molecular dynamics (MD) with reactive force fields (ReaxFF) to study the impact sensitivity of energetic materials. It has been applied to simulation of 1,3,5-trinitrohexahydro-s-triazine (RDX) crystal subjected to high-rate compression typical at the detonation front. The obtained results show that at lower compression ratio x = 1-V/V040%) all molecules decompose very quickly. We have observed both primary and secondary reactions during the decomposition process as well as production of various intermediates (NO2, NO, HONO, OH) and final products (H2O, N2, CO, CO2). The results of strain-driven compression-expansion modeling are in a good agreement with previous ReaxFF-MD shock simulations in RDX. Proposed approach might be useful for a quick test of sensitivity of energetic materials under conditions of high strain rate loading

Dasgupta, S.

Goddard, W. A., III

van Duin, A. C. T.

Zhang, L.

Zybin, S. V.

English

L. Zhang

Crossref

  SHOCK INDUCED DECOMPOSITION AND SENSITIVITY OF ENERGETIC MATERIALS BY REAXFF MOLECULAR DYNAMICS  L. Zhang, S. V. Zybin, A. C. T. van Duin, S. Dasgupta, and W. A. Goddard III  Materials and Process Simulation Center, M/C 139-74 California Institute of Technology, Pasadena, California 91125  Abstract. We develop strain-driven compression-expansion technique using molecular dynamics (MD) with reactive force fields (ReaxFF) to study the impact sensitivity of energetic materials. It has been applied to simulation of 1,3,5-trinitrohexahydro-s-triazine (RDX) crystal subjected to high-rate compression typical at the detonation front. The obtained results show that at lower compression ratio x = 1–V/V0<40% only a few of RDX molecules are decomposed, while for higher compressions (x>40%) all molecules decompose very quickly. We have observed both primary and secondary reactions during the decomposition process as well as production of various intermediates (NO2, NO, HONO, OH) and final products (H2O, N2, CO, CO2). The results of strain-driven compression-expansion modeling are in a good agreement with previous ReaxFF-MD shock simulations in RDX. Proposed approach might be useful for a quick test of sensitivity of energetic materials under conditions of high strain rate loading.  Keywords: molecular dynamics, explosive, detonation, energetic materials, sensitivity PACS:  02.70.Ns, 34.20.-b, 82.33.Vx, 82.40.Fp  INTRODUCTION  Impact sensitivity of energetic materials (EM) is important property for the handling of explosive compounds. Determination, evaluation and prediction of impact sensitivity have stimulated numerous studies in last decades [5-13]. It has been found that the impact sensitivity is influenced by various molecular parameters such as the oxygen balance [14], the molecular electro-negativity [15-17], the lengths of the trigger bonds [18-20], and the charge distribution asymmetry around these bonds both in the ground [21-23] and in the excited states [24-27]. However, there is no comprehensive understanding of atomistic mechanisms governing the impact sensitivity and lack of computational techniques for its quick assessment.  In order to test and evaluate the sensitivity of pure explosive crystals, we introduce molecular dynamics (MD) approach equipped with the reactive force field (ReaxFF) capable to simulate the decomposition processes in energetic materials. The ReaxFF is a reactive force field developed for various reactive systems. In this work we apply our approach to study the decomposition of RDX pure crystal and evaluate its sensitivity under conditions of very high-rate compression typical at the front of detonation wave. Such simulation studies can contribute to our understanding of the complex physicochemical processes that underlie the detonation of these materials and can led to methods for modifying the explosive or propellant formulations in order to obtain better performance and safety properties.    SIMULATION METHOD    We have developed strain-driven compression-expansion procedure coupled with MD simulations, as shown in Figure 1. It starts with a zero-pressure structure (initial cell volume: V0) and includes four steps: (1) nonequilibrium MD with gradual step-by-step uniaxial compression of the simulation cell to a new volume V=V0 (100–x)% at 585Downloaded 21 Aug 2006 to 131.215.240.9. Redistribution subject to AIP license or copyright, see http://proceedings.aip.org/proceedings/cpcr.jsphigh compression rate (close to the detonation velocity), where x=(V/V0)*100% is the volume compression ratio; (2) running 1-ps NVE MD simulation for a system in compressed cell; (3) nonequilibrium MD with step-by-step uniaxial expansion of the cell to V =V0 (100+x)% backward in the compression direction at one third of the compression rate; (4) running 4-ps NVE MD simulation after the expansion. Here, we report the simulations in RDX crystal with six compression ratios x=30, 35, 38, 40, 42, and 45%. The compression rate is 8.76 km/s (which is close to the RDX detonation velocity).  The packing structure of RDX cell was taken from the Cambridge Structural Database (CSD). It has been minimized using the ReaxFF and then equilibrated at T=300 K for 5.0ps. To remove residual stresses, the NPT-MD has been performed at zero pressure for 2.5ps. The temperature of the system was controlled by Berendsen thermostat with damping constant of 50 fs. The final structure has been used to run the four-stages ‘compression-expansion’ procedure (see Fig. 1) to test the reactivity of RDX at different compression ratios.  The integration time was 0.25 fs in the NVT and NPT equilibrium MD simulations, and 0.1 fs in the compression-expansion simulations. The bond order cutoff for molecule recognition used in the species analysis for all cases was set to 0.3.  RESULTS AND DISCUSSION  The results of are plotted in Figs. 2(a)-(c) for the system temperature, pressure, and total number of fragments per RDX molecule. It shows that the degree of decomposition of RDX is changed dramatically above certain compression threshold.  For the lowest compression ratio x=30%, the system temperature always stays below 1200 K and the number of fragments per RDX molecule remains 1.0 during the simulation process except for a short period in the compression region. There the number of fragments becomes less than one because some of the molecules come very close to each other and form a pseudocluster which cannot be discriminated by recognition procedure using just a simple fixed bond-order cutoff criteria. The degree of such ‘clusterization’ increases when the compression ratio grows up in the beginning of the first simulation stage (see Figure 3b). However, some of the RDX molecules even at this stage are 0100020003000400050000.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0Time, psTemperature, K45%42%40%38%35%30%(a)0.01.02.03.04.05.06.07.00.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0Time, psFragments / RDX molecule 45%42%40%38%35%30% (b)010000200003000040000500000.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0Time, psPressure, MPa45%42%40%38%35%30%(c)compression expansion 1st-NVE 2nd-NVE  FIGURE 2. The RDX simulation results: (a) system temperature, (b) total number of fragments, and (c) pressure. Compression x=30, 35, 38, 40, 42, and 45% V0(100 +x) % Expansion V0 (100-x) % Compression TimeVolume 1st NVE 2nd NVEV0  FIGURE 1. Four stages of strain-driven “compression-expansion” procedure to simulate high-rate deformationof energetic materials at the detonation front. 586Downloaded 21 Aug 2006 to 131.215.240.9. Redistribution subject to AIP license or copyright, see http://proceedings.aip.org/proceedings/cpcr.jsp FIGURE 5. Product frequencies per molecule obtained from the piston-driven shock simulation in RDX cell with 64 RDX molecules at piston velocity up=5 km/s. get dissociated in simulations with x>40% while others remain highly strained under compression. At highest compression ratio of x=45%, the system temperature increases dramatically up to 4520 K. Such sharp increase in the temperature is due to the initiation of chemical reactions in the system when chemical bonds break off under high temperature and pressure, and new products (H2O, N2, CO, and CO2) are formed providing a positive energy balance. The number of fragments per molecule grows up to ~3.1 at the expansion stage with a further increase to 5.9 during the NVE stage. In order to determine the critical compression ratio for initiation of the decomposition of RDX crystal, we measured the temperature and the total number of fragments at the end of each stage (i.e., compression, 1st-NVE, expansion, and 2nd-NVE). Figures 3(a) and 3(b) display the temperature and fragments vs. compression ratio at different stages. At lower compression ratios (x<40%), the temperature increases very little at all stages. It almost does not change at the end of expansion and 2nd-NVE stages, which correlates with a small change in the number of fragments (Figure 3b). However, the temperature and fragments increase dramatically when the compression ratio x>40%. For example, the final temperatures are 2790K and 4520K and the fragments per RDX molecule are 3.6 and 5.9 for x=42 and 45%, respectively. Our results suggest that the critical compression threshold could be ~40% for fast initiation of RDX at the compression rate of 8.76 km/s. We also studied the evolution of the system pressure. At the compression stage, the pressure attains ~13 GPa for the lowest compression ratio x=30%, while it rises up to ~45 GPa for the highest ratio of 45%, overshooting the experimental value of 33.8Gpa [1]. For the threshold value of x=40%, the pressure at the end of compression remains about 25 GPa, and the number of fragments is 5001500250035004500550025 30 35 40 45 50C o m p re s s io n  ra tio , %Temperature, KC ompre ssion1st-N VEE xpansion2nd-N VE0 .01 .02 .03 .04 .05 .06 .07 .025 30 35 40 45 50C o m p re s s io n  ra tio , %Fragmants / RDX molecule C o m p r e s s io n1 s t-N VEEx p a n s io n2 n d -N VE(a )(b )FIGURE 3. (a) Temperature and (b) fragments vs. compression ratio for RDX at different stages: compression, 1st-NVE, expansion, and 2nd-NVE.FIGURE 4. A detail species analysis for the RDXcrystal at the compression ratios of x=45%. 587Downloaded 21 Aug 2006 to 131.215.240.9. Redistribution subject to AIP license or copyright, see http://proceedings.aip.org/proceedings/cpcr.jspslowly increasing up to 1.8 during the rest of simulation. Besides, the final pressure after the expansion remains relatively small in comparison to 4.4 and 6.4 GPa observed in the simulations with x=42 and 45%, correspondingly. Note that the pressure in the last two cases increases noticeably during the 2nd NVE stage (about 40 and 60%). It also indicates a critical change in the response of RDX crystal above the threshold of x=40%. Figure 4 give a detailed analysis of evolution of major products and intermediates in the simulation with x=45%. The RDX molecules decompose very quickly producing such products as NO2, NO, HONO, CO, CO2, H2O, N2, OH, and O2 in good qualitative agreement both with experiment [35] and our recent simulations of piston-driven shock compression of the RDX crystal (see Fig. 5).  In summary, we developed the ReaxFF-MD ‘compression-expansion’ modeling technique aimed to test reactivity of energetic materials under high strain rate conditions similar to those at the detonation front. The simulation results suggest that the ReaxFF can provide a computationally inexpensive tool to evaluate the reactivity and shock sensitivity of various energetic materials.  ACKNOWLEDGEMENTS  Funding was provided by ONR and ARO MURI grants.  REFERENCES 1. Cooper P.W., Explosive Engineering, Wiley-VCH, New York, 1996.  2. Yoh J. J., McCleland M. A., Maienschein J. L., Wardell F. F., J. of Computer-Aided Materials Design 10, 175 (2005).  3. Agrawal J.P., Prog. Energy Combust. Sci. 24, 1-30 (1998) 4. Balzer J.E., Proud W.G., Walley S.M., Field J.E., Combustion and Flame 135, 547 (2003).  5. Sharma J., Beard B.C., Chaykovsky M., J. Phys. Chem. 95, 1209-1213 (1991).  6. Zeman, S.  Propel.Expl. Pyrotech, 25, 66-74 (2000).  7. Edward J., Eybl C., Johnson B., Int. J. Quantum Chem. 100, 713–719 (2004).  8. Gruzdkov Y.A., Gupta Y.M., J. Phys. Chem. A 104, 11169-11176 (2000).  9. Wu C. J., Fried L. E., J. Phys. Chem. A 101, 8675-8679 (1997). 10. Nefati H., Cense J.-M., Legendre J.–J., J. Chem. Inf. Comput. Sci. 36, 804 (1996).  11. Vaullerin M., Espagnacq A. Propel. Expl. Pyrotech. 23, 237-239 (1998).  12. Dubovik A. V., Combustion, Explosives, and Shock Waves, 38, 714 (2002).  13. Chidester S. K., Tarver C. M., Green L. G., Urtiew P. A., Combustion and Flame 110, 264 (1997). 14. Kamlet, M. J.; Adolph, H. G. Proceedings of the 7th Symposium (International) on Detonation; Annapolis, MD, 1981; pp.84-92.  15. Mullay, J. Explosives, Pyrotechnics 12, 60 (1987). 16. Mullay, J. Explosives, Pyrotechnics 12, 121 (1987). 17. Mullay, J. J. Am. Chem.Soc. 106, 5842 (1984). 18. Mullay, J. J. Am. Chem.Soc. 107, 7271 (1985). 19. Mullay, J. J. Am. Chem.Soc. 108, 1770-1775 (1986) 20. Kohno, Y., Maekawa, K., Tsuchioka, T. Hashizume, T., Imamura, A. Combustion and Flame, 96, 343-350 (1994).  21. Politzer, P., Seminario, J. M., Bolduc, P. R., Chem. Phys. Lett. 158, 463-469 (1989).  22. Murray, J. S., Lane, P., Politzer, P., Bolduc, P. R. Chem. Phys. Lett., 168, 135-139 (1990).  23. Politzer, P., Murray, J. S., Lane, P., Sjoberg, P., Adolph, H. G. Chem. Phys. Lett. 181, 78-82 (1991).  24. Delpuech, A., Cherville, J., Propelants, Explosives 1978, 3, 169-175.  25. Delpuech, A., Cherville, J., Propellants Explosives 1979, 4, 121-128.  26. Delpuech, A., Cherville, J., Propellants Explosives 1979, 4, 61-65.  27. Delpuech, A.; Cherville, J., Proceedings of the 7th Symposium (International) on Detonation; Annapolis, MD, 1981; pp 65-74.  28. Strachan A., van Duin A.C.T., Chakraborty D., Dasgupta S. and Goddard III W.A., Phys .Rev. Lett. 91, 09301 (2003).  29. Strachan A., Kober E., van Duin A.C.T., Oxgaard J. and Goddard III, W.A., J. Chem. Phys. 122, 054502 (2005). 30. van Duin A.C.T., Dasgupta S., Lorant F., Goddard III W.A., J. Phys. Chem. A 105, 9396 (2001).  31. van Duin A.C.T., Strachan A., Stewman S., Zhang Q., Xu X., and Goddard III W.A., J.Phys.Chem. A 107, 3803 (2003).  32. Zhang Q., Cagin T., van Duin A.C.T., Goddard III W.A., Qi Y. and Hector L., Phys. Rev. B 69, 045423 (2004).  33. Nielson K., van Duin A.C.T., Oxgaard J., Deng W., Goddard III W.A. J.Phys.Chem. A, 109, 493 (2005). 34. Cheung S., Deng W., van Duin A.C.T., Goddard III W.A.,  J. Phys. Chem. A, 109, 851 (2005). 35. McCrone W.C., in: Physics and Chemistry of the Organics Solid State (ed. by D. Fox et al), Wiley: New York, 1965; Vol II, pp 726-766. 36. Sorescu D.C., Rice B.M., Thompson D.L., J. Phys. Chem. B 102, 6692 (1998). 588Downloaded 21 Aug 2006 to 131.215.240.9. Redistribution subject to AIP license or copyright, see http://proceedings.aip.org/proceedings/cpcr.jsp

Shock Induced Decomposition and Sensitivity of Energetic Materials by ReaxFF Molecular Dynamics

Caltech Authors - Main

 
 
SHOCK INDUCED DECOMPOSITION AND SENSITIVITY OF 
ENERGETIC MATERIALS BY REAXFF MOLECULAR DYNAMICS 
 
L. Zhang, S. V. Zybin, A. C. T. van Duin, S. Dasgupta, and W. A. Goddard III 
 
Materials and Process Simulation Center, M/C 139-74 
California Institute of Technology, Pasadena, California 91125 
 
Abstract. We develop strain-driven compression-expansion technique using molecular dynamics 
(MD) with reactive force fields (ReaxFF) to study the impact sensitivity of energetic materials. It has 
been applied to simulation of 1,3,5-trinitrohexahydro-s-triazine (RDX) crystal subjected to high-rate 
compression typical at the detonation front. The obtained results show that at lower compression ratio 
x = 1–V/V0<40% only a few of RDX molecules are decomposed, while for higher compressions 
(x>40%) all molecules decompose very quickly. We have observed both primary and secondary 
reactions during the decomposition process as well as production of various intermediates (NO2, NO, 
HONO, OH) and final products (H2O, N2, CO, CO2). The results of strain-driven compression-
expansion modeling are in a good agreement with previous ReaxFF-MD shock simulations in RDX. 
Proposed approach might be useful for a quick test of sensitivity of energetic materials under 
conditions of high strain rate loading. 
 
Keywords: molecular dynamics, explosive, detonation, energetic materials, sensitivity 
PACS:  02.70.Ns, 34.20.-b, 82.33.Vx, 82.40.Fp 
 
INTRODUCTION 
 
Impact sensitivity of energetic materials (EM) 
is important property for the handling of explosive 
compounds. Determination, evaluation and 
prediction of impact sensitivity have stimulated 
numerous studies in last decades [5-13]. It has been 
found that the impact sensitivity is influenced by 
various molecular parameters such as the oxygen 
balance [14], the molecular electro-negativity [15-
17], the lengths of the trigger bonds [18-20], and 
the charge distribution asymmetry around these 
bonds both in the ground [21-23] and in the excited 
states [24-27]. However, there is no comprehensive 
understanding of atomistic mechanisms governing 
the impact sensitivity and lack of computational 
techniques for its quick assessment.  
In order to test and evaluate the sensitivity of 
pure explosive crystals, we introduce molecular 
dynamics (MD) approach equipped with the 
reactive force field (ReaxFF) capable to simulate 
the decomposition processes in energetic materials. 
The ReaxFF is a reactive force field developed for 
various reactive systems. In this work we apply our 
approach to study the decomposition of RDX pure 
crystal and evaluate its sensitivity under conditions 
of very high-rate compression typical at the front 
of detonation wave. Such simulation studies can 
contribute to our understanding of the complex 
physicochemical processes that underlie the 
detonation of these materials and can led to 
methods for modifying the explosive or propellant 
formulations in order to obtain better performance 
and safety properties.   
 
SIMULATION METHOD  
  
We have developed strain-driven compression-
expansion procedure coupled with MD 
simulations, as shown in Figure 1. It starts with a 
zero-pressure structure (initial cell volume: V0) and 
includes four steps: (1) nonequilibrium MD with 
gradual step-by-step uniaxial compression of the 
simulation cell to a new volume V=V0 (100–x)% at 
585
Downloaded 21 Aug 2006 to 131.215.240.9. Redistribution subject to AIP license or copyright, see http://proceedings.aip.org/proceedings/cpcr.jsp
high compression rate (close to the detonation 
velocity), where x=(V/V0)*100% is the volume 
compression ratio; (2) running 1-ps NVE MD 
simulation for a system in compressed cell; (3) 
nonequilibrium MD with step-by-step uniaxial 
expansion of the cell to V =V0 (100+x)% backward 
in the compression direction at one third of the 
compression rate; (4) running 4-ps NVE MD 
simulation after the expansion. Here, we report the 
simulations in RDX crystal with six compression 
ratios x=30, 35, 38, 40, 42, and 45%. The 
compression rate is 8.76 km/s (which is close to the 
RDX detonation velocity).  
The packing structure of RDX cell was taken 
from the Cambridge Structural Database (CSD). It 
has been minimized using the ReaxFF and then 
equilibrated at T=300 K for 5.0ps. To remove 
residual stresses, the NPT-MD has been performed 
at zero pressure for 2.5ps. The temperature of the 
system was controlled by Berendsen thermostat 
with damping constant of 50 fs. The final structure 
has been used to run the four-stages ‘compression-
expansion’ procedure (see Fig. 1) to test the 
reactivity of RDX at different compression ratios.  
The integration time was 0.25 fs in the NVT and 
NPT equilibrium MD simulations, and 0.1 fs in the 
compression-expansion simulations. The bond 
order cutoff for molecule recognition used in the 
species analysis for all cases was set to 0.3. 
 
RESULTS AND DISCUSSION 
 
The results of are plotted in Figs. 2(a)-(c) for 
the system temperature, pressure, and total number 
of fragments per RDX molecule. It shows that the 
degree of decomposition of RDX is changed 
dramatically above certain compression threshold.  
For the lowest compression ratio x=30%, the 
system temperature always stays below 1200 K and 
the number of fragments per RDX molecule 
remains 1.0 during the simulation process except 
for a short period in the compression region. There 
the number of fragments becomes less than one 
because some of the molecules come very close to 
each other and form a pseudocluster which cannot 
be discriminated by recognition procedure using 
just a simple fixed bond-order cutoff criteria. The 
degree of such ‘clusterization’ increases when the 
compression ratio grows up in the beginning of the 
first simulation stage (see Figure 3b). However, 
some of the RDX molecules even at this stage are 
0
1000
2000
3000
4000
5000
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0
Time, ps
Te
m
pe
ra
tu
re
, K
45%
42%
40%
38%
35%
30%
(a)
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0
Time, ps
Fr
ag
m
en
ts
 / 
R
D
X 
m
ol
ec
ul
e 45%
42%
40%
38%
35%
30% (b)
0
10000
20000
30000
40000
50000
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0
Time, ps
Pr
es
su
re
, M
Pa
45%
42%
40%
38%
35%
30%
(c)
compression 
expansion 
1st-NVE 
2nd-NVE 
 
FIGURE 2. The RDX simulation results: (a) system 
temperature, (b) total number of fragments, and (c) 
pressure. Compression x=30, 35, 38, 40, 42, and 45% 
V0(100 +x) % 
Expansion 
V0 (100-x) % 
Compression Time
V
ol
um
e 
1st NVE 
2nd NVE
V0 
 
FIGURE 1. Four stages of strain-driven “compression-
expansion” procedure to simulate high-rate deformation
of energetic materials at the detonation front. 
586
Downloaded 21 Aug 2006 to 131.215.240.9. Redistribution subject to AIP license or copyright, see http://proceedings.aip.org/proceedings/cpcr.jsp
 
FIGURE 5. Product frequencies per molecule obtained 
from the piston-driven shock simulation in RDX cell 
with 64 RDX molecules at piston velocity up=5 km/s. 
get dissociated in simulations with x>40% while 
others remain highly strained under compression. 
At highest compression ratio of x=45%, the 
system temperature increases dramatically up to 
4520 K. Such sharp increase in the temperature is 
due to the initiation of chemical reactions in the 
system when chemical bonds break off under high 
temperature and pressure, and new products (H2O, 
N2, CO, and CO2) are formed providing a positive 
energy balance. The number of fragments per 
molecule grows up to ~3.1 at the expansion stage 
with a further increase to 5.9 during the NVE stage. 
In order to determine the critical compression 
ratio for initiation of the decomposition of RDX 
crystal, we measured the temperature and the total 
number of fragments at the end of each stage (i.e., 
compression, 1st-NVE, expansion, and 2nd-NVE). 
Figures 3(a) and 3(b) display the temperature and 
fragments vs. compression ratio at different stages. 
At lower compression ratios (x<40%), the 
temperature increases very little at all stages. It 
almost does not change at the end of expansion and 
2nd-NVE stages, which correlates with a small 
change in the number of fragments (Figure 3b). 
However, the temperature and fragments increase 
dramatically when the compression ratio x>40%. 
For example, the final temperatures are 2790K and 
4520K and the fragments per RDX molecule are 
3.6 and 5.9 for x=42 and 45%, respectively. Our 
results suggest that the critical compression 
threshold could be ~40% for fast initiation of RDX 
at the compression rate of 8.76 km/s. 
We also studied the evolution of the system 
pressure. At the compression stage, the pressure 
attains ~13 GPa for the lowest compression ratio 
x=30%, while it rises up to ~45 GPa for the highest 
ratio of 45%, overshooting the experimental value 
of 33.8Gpa [1]. For the threshold value of x=40%, 
the pressure at the end of compression remains 
about 25 GPa, and the number of fragments is 
500
1500
2500
3500
4500
5500
25 30 35 40 45 50
C o m p re s s io n  ra tio , %
Te
m
pe
ra
tu
re
, K
C ompre ssion
1st-N VE
E xpansion
2nd-N VE
0 .0
1 .0
2 .0
3 .0
4 .0
5 .0
6 .0
7 .0
25 30 35 40 45 50
C o m p re s s io n  ra tio , %
Fr
ag
m
an
ts
 / 
R
D
X 
m
ol
ec
ul
e C o m p r e s s io n
1 s t-N VE
Ex p a n s io n
2 n d -N VE
(a )
(b )
FIGURE 3. (a) Temperature and (b) fragments 
vs. compression ratio for RDX at different stages: 
compression, 1st-NVE, expansion, and 2nd-NVE.
FIGURE 4. A detail species analysis for the RDX
crystal at the compression ratios of x=45%. 
587
Downloaded 21 Aug 2006 to 131.215.240.9. Redistribution subject to AIP license or copyright, see http://proceedings.aip.org/proceedings/cpcr.jsp
slowly increasing up to 1.8 during the rest of 
simulation. Besides, the final pressure after the 
expansion remains relatively small in comparison 
to 4.4 and 6.4 GPa observed in the simulations with 
x=42 and 45%, correspondingly. Note that the 
pressure in the last two cases increases noticeably 
during the 2nd NVE stage (about 40 and 60%). It 
also indicates a critical change in the response of 
RDX crystal above the threshold of x=40%. 
Figure 4 give a detailed analysis of evolution of 
major products and intermediates in the simulation 
with x=45%. The RDX molecules decompose very 
quickly producing such products as NO2, NO, 
HONO, CO, CO2, H2O, N2, OH, and O2 in good 
qualitative agreement both with experiment [35] 
and our recent simulations of piston-driven shock 
compression of the RDX crystal (see Fig. 5).  
In summary, we developed the ReaxFF-MD 
‘compression-expansion’ modeling technique 
aimed to test reactivity of energetic materials under 
high strain rate conditions similar to those at the 
detonation front. The simulation results suggest 
that the ReaxFF can provide a computationally 
inexpensive tool to evaluate the reactivity and 
shock sensitivity of various energetic materials. 
 
ACKNOWLEDGEMENTS 
 
Funding was provided by ONR and ARO MURI grants. 
 
REFERENCES 
1. Cooper P.W., Explosive Engineering, Wiley-VCH, 
New York, 1996.  
2. Yoh J. J., McCleland M. A., Maienschein J. L., 
Wardell F. F., J. of Computer-Aided Materials 
Design 10, 175 (2005).  
3. Agrawal J.P., Prog. Energy Combust. Sci. 24, 1-30 
(1998) 
4. Balzer J.E., Proud W.G., Walley S.M., Field J.E., 
Combustion and Flame 135, 547 (2003).  
5. Sharma J., Beard B.C., Chaykovsky M., J. Phys. 
Chem. 95, 1209-1213 (1991).  
6. Zeman, S.  Propel.Expl. Pyrotech, 25, 66-74 (2000).  
7. Edward J., Eybl C., Johnson B., Int. J. Quantum 
Chem. 100, 713–719 (2004).  
8. Gruzdkov Y.A., Gupta Y.M., J. Phys. Chem. A 104, 
11169-11176 (2000).  
9. Wu C. J., Fried L. E., J. Phys. Chem. A 101, 8675-
8679 (1997). 
10. Nefati H., Cense J.-M., Legendre J.–J., J. Chem. Inf. 
Comput. Sci. 36, 804 (1996).  
11. Vaullerin M., Espagnacq A. Propel. Expl. Pyrotech. 
23, 237-239 (1998).  
12. Dubovik A. V., Combustion, Explosives, and Shock 
Waves, 38, 714 (2002).  
13. Chidester S. K., Tarver C. M., Green L. G., Urtiew 
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Combustion and Flame 110,

Explosive Engineering,

Propellants Explosives

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Vol II,

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Shock Induced Decomposition and Sensitivity of Energetic Materials by ReaxFF Molecular Dynamics

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