Experimental and numerical studies of a near-field blast loading model for cylindrical charges

Abstract

In the current practice of blast-resistant design, blast loads are determined by the Kingery and Bulmash charts in accordance with a database of free-air blasts of spherical charges and surface bursts of hemispherical charges initiated at the center. However, most charges are closer to cylinders in geometry. In addition, charge shapes and initiation configurations significantly affect blast loads under a near-field blast scenario. Therefore, it is imperative to develop a near-field blast loading model for cylindrical charges that can account for the effects of both charge shape and initiation configuration in blast-resistant design. Compared with incident blast loads, reflected blast loads are more relevant because the latter can be directly used for blast-resistant design. Accordingly, in this paper, experimental and numerical studies were performed to develop a near-field blast loading model for cylindrical charges in terms of the peak reflected overpressure and the maximum reflected impulse. Two series of tests were conducted with either one-end-initiated or both-end-initiated cylindrical charges to obtain reflected blast loads with different scaled distances. It was found that the spatial distribution of blast loads along the axial direction of the charges was extremely non-uniform. Then, high-efficiency numerical models were built using 2D to 3D mapping techniques. After being validated against experimental results, numerical models were employed to simulate the blast loads generated by cylindrical charges with different length-to-diameter ratios and initiation configurations (one-end, center, and both-end initiations) with scaled distances ranging from 0.2 to 1.0 m/kg\(^{\mathrm {1/3}}\). To develop the blast loading model, the peak reflected overpressure and the maximum reflected impulse at the center of a rigid reflection surface were firstly determined by curve fitting as the benchmark blast loads, which were expressed as functions of scaled distance and length-to-diameter ratio, and then the benchmark blast loads were used to normalize the blast loads at different locations. Accordingly, the spatial distribution of blast loads can be described with the benchmark blast loads and a spatial load distribution function, in which the latter is determined by surface fitting of extensive numerical results. The results indicate that the blast loading model developed is able to predict the blast load with considerable accuracy.