The Numerical Simulation on Co-Damage Effectiveness of Penetration and Explosion Made by BLU-113

Zeng Liang, Wang Wei-li, Zhu Jian-fang Naval Aeronautical and Astronautical University

Yantai, China Steel1026@163.com

Abstract—BLU-113 is earth penetrator warhead commonly used. It has been simulated by using LS-DYNA finite- element software to analyze damage effectiveness of BLU-113, which BLU-113 attacks underground protective works under different deepness from 10 to 22m. In the simulation, shotcrete layers, anchor-hold rocks and loose rocks are taken into account. The penetration process and explosive process of BLU-113 both are simulated. The calculating results reveal that co-damage effectiveness of penetration and explosion can’t be ignored in the study on earth penetrator weapon. And we may pay attention to BLU-113, because its damage effectiveness is very remarkable in the simulation.

Keywords-protective works; earth penetrator weapon; numerical simulation; penetration

I. INTRODUCTION The BLU-113 is a 4,440-lb (1,996 kg) high explosive

penetrator warhead designed to destroy hardened targets such as buried bunkers. This warhead has been provided to the GBU-28 Bunker Buster laser-guided bomb, the cancelled GBU-37/B Global Positioning System Aided Munition (GAM) intended for use on the B-2 bomber. The casing is made from HP9420 alloy steel to provide target penetration capabilities. GBU-28 is a special weapon developed for penetrating hardened Iraqi command centers located deep underground, which is a 5,000-pound laser-guided conventional munition. And GBU-28 is capable of penetrating more than 20 feet of reinforced concrete and deeper than 100 feet underground [1, 2].

Judging from the current published literature on numerical simulation of damage effect on earth penetrator weapon, there are two major shortages. Firstly, the influence of casing with the explosion damage effect basically has not been considered. However, the outcome of numerical simulation shows that explosion damage effect decreases with increasing of casing thickness when charges have casing. But sheet casing can enhance explosion damage effect compared to non-casing. The reason may be that detonation gathering effect is dominant if casing of charge is sheet. The detonation gathering effect can enhance explosion damage effect. When casing thickness increases, the casing breaking energy will also increase. If casing exceeds a certain thickness, the casing breaking energy will counteract the detonation gathering effect and reduce explosion damage effect. Because the casing of earth penetrator weapon is thick

generally, the influence of casing on explosion damage effect can’t be ignored in the study on the damage effect of earth penetrator weapon [3].

Secondly, the penetration damage effect and explosive damage effect are basically considered separately in published literature. And at involved norms in China, it only considered the penetration depth and explosion of packing factor, did not take into account the joint damage effect of penetration and explosion. But Zuo-Kui, through the experimental study, believed that the joint damage effect of penetration and explosion in rock is very obvious, can not be ignored [4, 5]. If we can simulate the entire process from penetration to explosion damage in numerical analysis, we can make up the above insufficiency at the same time. In LS-DYNA software, the keyword * INITIAL_DETONATION provided delay detonation function. It allows us to solve this problem [6].

We applied a large-scale finite element software ANSYS/LS-DYNA to simulate the BLU-113 attacking underground cavern protective works at different depth (from cavern vault to ground 10~22m). In the numerical simulation, the joint damage effect of penetration and explosion had been considered. And the cavern protective works actual status, shotcrete layers, bolted rockmass and loose rocks excavated, as far as possible were taken into account.

II. GEOMETRY MODELING AND MESH DIVISION The width of Entire underground protective works

geometry model is 7.0 m. It takes 2.0 m along the cavern longitudinal thickness. It is 2.0m from the cavern bottom floor to model base surface. The cavern is round arch structure with straight wall, clear span length 3.6m, straight wall high 2.0m, rise of arch 1.5m. From vault to ground entire protective layer thickness is 10-22m, divided 10m, 13m, 16m, 19m and 22m five conditions for numerical calculation, see Tab.2. And shotcrete thickness is 0.15m, bolted rockmass thickness 2.0m, loose rockmass thickness is 1.0m, the rest is the natural rockmass.

The parameters of BLU-113 can be seen at Tab.1. The computation uses 1/4 model, exerts the symmetrical

restraint in the plane of symmetry, on other establishes transmission boundary. The three-dimensional finite element model sees Fig.1, Fig.2.

To ensure comparability of the numerical simulation, the meshes of BLU-113, shotcrete layers, bolted rockmass and

2010 Second International Conference on Computer Modeling and Simulation

978-0-7695-3941-6/10 $26.00 © 2010 IEEE

DOI 10.1109/ICCMS.2010.233

76

2010 Second International Conference on Computer Modeling and Simulation

978-0-7695-3941-6/10 $26.00 © 2010 IEEE

DOI 10.1109/ICCMS.2010.233

76

loose rocks in the six kind of working conditions all remain unchanged, while the amount of natural rock meshes increased with the depth, but the mesh size unchanged. On the one hand as a result of computing resource limit, on the other hand to speed up the computation speed, only on the local penetration pathway the meshes are refined. Please see Fig.3. All meshes are the hexahedron Lagrange meshes. Penetration contact algorithm is used in MOP penetration rock. Model node and element numbers see also Tab.2.

The simulation process's time course is: in 0 times, BLU-113 is located at above the natural rock mass 0.01m place, the initial penetration speed is 400m/s; After the penetration starts, in 30ms, charge detonated; when 33ms, charge explosion finished basically, to avoid charge element excessively abnormal influence computation speed, charge elements were deleted; when 40ms, BLU-113 explosive influence ended on the whole, so calculation stopped.

TABLE I. PARAMETERS OF BLU-113

charge Charge length Charge Diameter Charge Weight Tritonal 388.6 cm 25.4cm 294kg

TABLE II. MODEL BASIC SITUATION

Model name GBU_155 GBU_185 GBU_215 GBU_245 GBU_275Model height 15.5m 18.5m 21.5m 24.5m 27.5m

vault to ground 10m 13m 16m 19m 22m vault to

Penetrator forehead

(Approximately)

4m 7m 10m 13m 16m

The total number of nodes 345711 423411 501111 578811 656511

The total number of elements

326974 401434 475894 550354 624814

Figure 1. Three-dimensional finite element model

Figure 2. Model of BLU-113

Figure 3. BLU-113 mesh at penetration

III. MATERIAL MODEL AND COMPUTATION PARAMETER Charge is described with high explosive constitutive

equations and equation of state (JWL*MAT-HIGH-EXPLOSIVE-BURN and EOS-JWL), parameters see Tab.3. Casing of BLU-113 uses Johnson-Cook plastic model, material parameters see Tab.4. Natural rock, shotcrete layers, bolted rockmass and loose rocks all use H-J-C material model, material parameters see Tab.5. The above various materials model did not give unnecessary detail at this. Please refer to the related literature.

TABLE III. PARAMETERS OF CHARGE IN CALCULATION

A/(Pa) B/(Pa) R1 R2 ω E0/(J) D/(m/s) PCJ/(Pa)5.242E+11 7.678E+9 4.20 1.10 0.34 8.50E+9 7980 2.95E+10

TABLE IV. PARAMETERS OF CASING IN CALCULATION

ρ/(kg·m-3) G(Pa) ν A B N PC C/(m/s)7900 8.10E+10 0.285 8.920E+8 6.100E+8 0.26 -9.0E+11 4600

TABLE V. PARAMETERS OF ROCK AND SHOTCRETE IN CALCULATION

Material ρ/(kg·m-3) G/(Pa) FC/(Pa) T/(Pa)Natural rock 2450 12.6E+9 38E+6 4E+6 Loose rock 2000 8.6E+9 28E+6 4E+6

Bolted rockmass 2440 14.86E+9 48E+6 5E+6 Shotcrete layers 2600 18.00E+9 60E+6 6E+6

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IV. CALCULATED RESULT AND ANALYSIS

A. Numerical Simulation Analysis about Penetration Fig.4 is the penetration depth/time curve of BLU-113.

Fig.5 is the penetration speed/time curve of BLU-113. For all five kinds of working conditions, the penetration depths were basic consistent, the residual velocity as well. This indicated that above 13m protective layer thickness has been equal basically to the semi-infinite thickness regarding BLU-113.

The BLU-113 penetration depth obtained from numerical simulation is 5.996m, been basically consistent with penetration depth 6m disclosed by the U.S army for reinforced concrete. Therefore the penetration simulation was basic credible.

Figure 4. Penetration depth/time curve

Figure 5. Penetration speed/time curve

Figure 6. Penetration acceleration/time curve

Found from Fig.4 and Fig.5 in contrast, BLU-113 already penetrated 5.1m at 20ms, but the residual velocity still had 130m/s. This shows that, in certain penetration speed range, the penetration speed is quicker, the penetration depth is deeper.

Discovered from Fig.6 penetration acceleration/time curve, when BLU-113 penetrated rock mass at beginning,

the resistance rapidly rose. The resistance acceleration reached at the peak at 3ms when BLU-113 penetrated into the rock 1m. Hereafter with the speed constant decreasing, the resistance acceleration is constantly decreasing. This indicated that the penetration resistance and the penetration speed are positive related.

Shown in Fig.7 the penetration crater diameter was similar with BLU-113 diameter. However as shown in Fig.8 damage parameter, the damage diameter (damage parameter D>0.5) is nearly two times BLU-113 diameter. This indicated that MOP, in the penetration process, made the rock nearby the penetration road to receive certain damage. It had certain influence inevitably to the damage which charge explosion produced. Therefore, joint damage effect of penetration and explosion can’t be ignored in the study on earth penetrator weapon.

In the 30ms penetration process, at five kinds of working conditions shotcrete and bolted rockmass did not have any visible damage.

Figure 7. Penetration crater

Figure 8. Penetration crater by damage parameter

B. Numerical Simulation of MOP Charge Explosion Fig.9, Fig.10 is the stable explosion cavity after charge

explosion. The maximum diameter of explosion cavity approximately is 0.95m, but BLU-113 diameter is 0.37m, and the charge diameter approximately is 0.254m. Then, explosion cavity diameter is 3.74 times the charge diameter. According to experience, it shows that if we did not consider penetration, explosion cavity diameter is charge diameter about 1.9 to 2.5 times. This indicated the pre-damage created by penetration is advantageous in expansion explosive cavity.

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Figure 9. Explosion cavity after charge explosion

Figure 10. Explosion cavity indicated by damage parameter

Figure 11. The final damage in GBU-155

Figure 12. The final damage in GBU-185

Figure 13. The final damage in GBU-215

Figure 14. The final damage in GBU-245

Figure 15. The final damage in GBU-275

Fig.11~ Fig.15 respectively shows the final damage of shotcrete and bolted rockmass at five kinds of working conditions. Compared five figures, it can be find that as the protective layer thickness increases, the less damage. The destroyed areas were mainly concentrated in the vault, the link with vertical wall and arch, as well as the vertical wall root. When protective layer thickness achieves 22m, the destruction was quite already slight. The destruction mainly was a penetration crack at the link with vertical wall and arch. Viewed form collapse Resistance, underground protection works can resist the attack of BLU-113 at GBU_245 working conditions, 19m from vault to ground, 13m approximately vault to Penetrator forehead.

V. CONCLUSION AND SUGGESTION According to the above numerical simulation and

analysis, the following basic conclusions and suggestion can be obtained:

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1) Applying three dimension numerical simulation to the entire process of penetration and explosion, May avoid tradition analysis method error which brings directly charge in pre-calculated position, because of neglecting the penetration process. And the method can be truer reflection of the damage effect of penetration and explosion on earth penetrator weapons.

2) The damage effect of BLU-113 is very remarkable. It is at least 19m buried depth the underground protection works, clear span length 3.6m, III-class rockmass, shotcrete and rock bolt supporting, may resist the attack of BLU-113.

REFERENCES [1] Guided bomb unit-28 (gbu-28) blu-113 penetrator..Available:

http://tech.military.com/equipment/view/88693/guided-bomb-unit-28-(gbu-28)-blu-113-penetrator.html

[2] BLU-113/B, A/B Penetrator Warhead. Available: http://www.globalsecurity.org/military/systems/munitions/blu-113.htm

[3] L. Zeng , W.L. Wang, and J.F. Zhu, “Influence of casing on blasting effect of earth penetrator weapon”, Journal of PLA University of Science and Technology, vol. 8, no. 5, pp. 501-504, October 2007.

[4] B.P. Li and W.B. Lu, “Numerical simulation for the damage of concrete gravity dam under horizontal penetration and explosion of GBU-28”, BLASTING, vol. 24, no. 1, pp. 1-5, February 2007.

[5] K. Zuo, X.M. Zeng, and S.M. Li, “Test Study on the Penetration and Explosion of Long-rod Projectile in Rock Medium”, presented at 15th nation structural engineering academic conference, Beijing, China, June 12–14, 2006, Paper collection III, pp. 469-475.

[6] Livermore Software Technology Corporation. LS-DYNA Keyword User’s Manual .2001.

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