PSI - Issue 14

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

192

2

Keywords: Blast Effect; RHA Steel; Damage Effect; Explosive Shape Effect;

Nomenclature ρ e

Explosive density; kg/m 3 Air density; kg/m 3

ρ a

JWL constant; Pa

a, b

R 1 , R 2 , ω JWL constant; D

Detonation velocity; m/s Specific internal energy; J/m 3 CJ detonation pressure; Pa Specific heat; J/kg °C Ratio of specific heat;

E

Pcj

q γ

1. Introduction Ammunitions are used for damaging the targets using various terminal effects. The terminal effects like blast, fragmentation, penetration, perforations and other effects are used. Land based munitions are used in defence applications for protecting the boarders of the country. Effect of these munitions is studied for achieving the desired damage. These munitions are used for causing the damage to enemy vehicles. Mainly two types of vehicles are in use in defence applications i.e. tracked and wheeled vehicles. It is well known that Anti-tank (AT) munitions are a serious threat against all vehicles including trucks, armoured personnel carriers (APCs), and main battle tanks (MBTs). The anti-tank munitions are used for causing damage by penetration of metal jet through the belly and damage of tracks using blast effects. Damage of vehicles caused by anti-tank munitions is mostly credited to the transferred shock waves in case of blast type of munitions. These munitions have explosive charges of cylindrical or rectangular bar shape depending on the requirement of lethality and coverage area. Effect of explosive charge shape on the peak pressures at near and larger scale distances for spherical, cylindrical and planer charges are briefly discussed in AMCP Pamphlets (1974). Peles et al. (2008) have studied the factors influencing armour damage that includes the explosive charge's geometric shape (cylindrical, spherical, cubic), standoff distances beneath the target, charge arrangement (buried flush with the surface, surface, above ground and soil type properties. Heider and Klomfass (2008) have studied the effect of buried depth on specific momentum with spatial distribution. Hoyos et al. (2011) have studied the dependence of mass of the explosive, reaction mass, depth of burial and standoff distance in energy transferred to a rigid objective using a specific soil. Held (2009) has divided the blast load into a close-field effect with the bulge in the belly plate and the global effect which accelerates the total vehicle with enormous force (magnitudes) and leads to damage on separated masses. Shekhar and Shekhar (2017) brought out that free field incident blast pressure by detonation of explosive charges at intermediate scaled distances between 0.5 to 3 are simulated mathematically using power law. The blast pressure of an explosive at certain scaled distance has an instantaneous peak followed by sharp decline in few milliseconds duration. TNT equivalence of explosives is considered for the calculation of peak over pressure and duration of positive pressure phase using empirical relationships. Björn et al. (2011) have studied the damage due to buried land mines in the near-field region. A spherical charge of 0.75 kg and density 1500 kg/m 3 have the near-field region extends to about 1 m from the explosive center. Experimentally, it is usually difficult to measure for pressure history in this region. If the explosive is confined in any way, the determination of the load acting on a structure would be even more difficult and less generalized. The effect of blast load in the near field of explosive charge is not possible to be predicted with simple empirical relationships. Also, further change in pressure due to shape of explosive in the near field region makes it impossible to determine. Chapman et al. (1995) have carried out 2-d autodyne simulations for influence of various parameters for blast pressure simulations. In this paper, 2-D axis symmetry simulations were carried out using Autodyne software. Blast pressure were verified with experimentally measured blast pressures of small quantity of RDX/Wax and large quantity of