Hezi Grisaro

A Modified Energy Method to Assess the Residual Velocity of Non-Deforming Projectiles That Perforate Concrete Barriers

In assessing vulnerability of a concrete barrier it is important to know the projectiles residual velocity, in case of perforation. The residual velocity is a measure of the resistance level provided by the barrier in case it is breached. It is also an important parameter in studying the response of barriers, whether experimentally or analytically. This paper proposes a formula to evaluate the residual velocity of a perforating non-deforming projectile. It is based on a semi-empirical approach that consists of theoretical assumptions regarding the damaged barrier under striking velocities that are higher than the perforation velocity and on empirically-calibrated parameters. The main hypothesis is that once a concrete barrier is perforated part of the projectiles striking energy is dissipated through fracture of the ejecting crater into concrete fragments, as well as additional cracking of the barrier. A parameter denoted γd is introduced as a function of the perforation-limit and striking velocities, and thus a common regression formula is deduced. A suitable energy balance and additional pertinent physical assumptions lead to formulation of an expression for the residual velocity, based on the knowledge of the perforation velocity. This approach yields a non-dimensional expression for the residual velocity, which agrees well with published experimental results (different than the ones used for calibration of the models parameters).

Numerical investigation of explosive bare charge equivalent weight

Peak overpressure and impulse are the most important parameters in the explosive performance estimation. Available models commonly consider trinitrotoluene explosive as the standard charge. In this article, the trinitrotoluene equivalency factor is studied through verified one-dimensional numerical simulations. The equivalency factors for impulse and overpressure are different and found to be constant with the scaled distance (3–40 m/kg1/3), which means that a unique value for the equivalency factor is suitable for the equivalency factor calculation for each distance. Comparison of the equivalency factor with available models shows that it strongly depends on the internal energy ratio of the explosive in interest, relative to trinitrotoluene, and a new formula for equivalency factor for overpressure is proposed. A verified simulation method is presented in which the explosive is modeled with an equivalent “air bubble” with the same internal energy and ideal gas equation of state. A new approach using the energy flux density calculation is presented to calculate the equivalency factor for impulse and overpressure from a single gauge measurement of overpressure-time history, at a specific distance.

Assessment of a Protective Wall Response to Explosive Loading Considering a Realistic Fragments Distribution

Design of structures to extreme loads include explosive loading that generates fragments impact and overpressure (blast). These structures are commonly made of reinforced concrete and they are called ‘protective structures’, where structures that are not designed to extreme loading can still be exposed to such loads. It is therefore important to evaluate the response and capacity of these structures under explosive loads. A common source of threat is a charge with a metal casing. After the charge detonates, the casing expands and ruptures into a large number of fragments of different masses.