Influence of charge shape and point of detonation of high explosive cylinders detonated on ground surface on blast-resistant design

Abstract

This paper studies how the properties of cylindrical explosive charges influence their generated blast loads (peak overpressure and maximum impulse) for surface burst scenarios, focusing on the aspect ratio (or length-to-diameter ratio) of the cylinder and the point of detonation of the charge. Specifically, the following three points of detonation are considered: the cylindrical charge is detonated at its bottom, middle or top centre, respectively. Numerical models are developed for both hemispherical and cylindrical charges, and are validated against experimental data available in the open literature. Important conclusions regarding the blast-resistant design are drawn from the parametric studies conducted using the validated models. Neglecting the effect of the cylindrical charge shape can result in underestimating the peak overpressure (maximum impulse) in the near field by a factor as high 6.6 (2.9). Therefore, the shape of the charge should be represented appropriately in the numerical simulations used for the blast-resistant design of protective structures subjected to near-field detonations. The generated shock front is known to smoothen out as the scaled distance increases, “healing” into a hemispherical one in the far field. However, cylindrical charges generate about 1.2 times higher blast loads in the far field than hemispherical ones do. The significance of the cylindrical charge shape effect on the peak overpressure (maximum impulse) resulting from the three considered points of detonation can be sorted in descending order as follows: bottom-centre-detonated > middle-centre-detonated > top-centre-detonated (top-centre-detonated > middle-centre-detonated = bottom-centre-detonated). The influence range is characterized by a scaled distance, above which the maximum value of the ratio of the peak overpressure (maximum impulse) of cylindrical charges and that of hemispherical charges converges to a constant value (1.2). The influence range for the overpressure is more or less the same (4.0 m/kg1/3) for the three different points of detonation, whereas the cylinder detonated at the bottom centre has a larger influence range for the impulse (8.0 m/kg1/3) than the cylinders detonated at the middle (4.2 m/kg1/3) and top centre (2.5 m/kg1/3).