PSI - Issue 14

Pankaj K. Choudha et al. / Procedia Structural Integrity 14 (2019) 191–198 Author name / Structural Integrity Procedia 00 (2018) 000–000

193

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RDX/TNT with RDX/wax. The properties of RDX/TNT and RDX/Wax explosive were validated. Further, 3-D simulations have been carried out for rectangular section and 'V' section bar charges. The shape of 'V' charge is inspired from shape charge phenomenon. Walters (1989) brought out that the hollow cavity charge was rediscovered by Charles E. Munroe and is well documented. The effect of change in explosive shapes causes change in peak over pressure and impulse based on numerical simulations have been presented here. This was further validated using the bar charges prepared in rectangular section and ‘V’ section with same explosive quantities. These were used against the RHA plates in experimental setup. The damage on the RHA plate have been studied. 2. Numerical simulations For numerical modelling of the blast effect, Autodyne software has been used. Pressures generated by explosive immediately after detonations are modelled using Euler Multi-material (explosive, air space etc.) solver in Autodyne using Jones, Wilkins and Lee (JWL) equation of state for explosive and ideal gas for air. The modelling has been done in three stages. In the first stage, the two types of explosive filled in polyethylene casing and cylindrical in shape were modelled using axis symmetric modelling for capturing near field blast pressures. In second stage, the near field pressure was further mapped to ideal gas air domain of larger size so that pressure at desired distance can be obtained by free expansion. Blast pressures were estimated at a distance of 1 m for small charge and 3 and 4 meters for larger charge. These blast pressures were further verified with the experimentally recorded pressure pulses. In the third stage, a three dimensional modelling of bar charges were carried out for rectangular section and ‘V’ section using symmetric boundary conditions about XY and YZ plane. The peak pressures and impulse for both charges were analyzed. 2.1 Modelling of small quantity of explosive charge (RDX/Wax) The explosive charge RDX/WAX (95/5) of Ø 47.2 mm and 12.8 mm height as shown in Fig. 1. was modelled. The charge was encased in 2 mm polyethylene casing. The polyethylene properties were directly used from Autodyne library. The strength of material is very low and therefore it does not affect the amplitude of blast pressure. The total mass of explosive is 29.7g. The 2-D Euler square domain of 200 mm × 200 mm size was created. The cell size of 1 mm was used. The air as ideal gas was filled round the charge. JWL equation of state given in equation (1) was used for modelling of explosive. The JWL equation of state describes the detonation product expansion for high energy explosive materials. JWL parameters for this explosive are given in Table. 1. The properties of air are given in Table 2. ܲ ൌ ܽ ቀͳ െ ఠ ோ ఎ భ ቁ ݁ ି ೃ ആ భ ൅ ܾ ቀͳ െ ఠ ோ ఎ మ ቁ ݁ ି ೃ ആ మ ൅ ߱ ߩ ݁ (1) Where η ൌ ρ ρ ౛ Table 1. JWL Material Parameters for RDX/WAX (95/5). ρ e a b R 1 R 2 ω D E Pcj 1.64 ×10 3 6.113×10 11 1.06500×10 10 4.4 1.2 0.32 8200 8.2×10 09 3.0×10 10

Table 2. Properties of Air. ρ a γ

T

o K

q

1.225 ×103 1.4

283

717.3

The blast pressure generated by the charge was further mapped to ideal gas Euler space of 500mm × 1500mm. The cell size of 5 mm was taken for this simulation. The pressure pulse was recorded at 1 m distance from simulation. The pressure pulse recorded using side on pressure gauges was super imposed in Fig. 1. (b). with the numerical simulation pulse. The pressure in far field ranges were matched for explosive charge RDX/WAX (95/5).