Predicting the Peak Pressure from the Curved Surface of Detonating Cylindrical Charges

Abstract

AbstractTrinitrotoluene (TNT) equivalency depends on knowing the relative strength of different explosives compared to TNT. However, most past work has been carried out only using spherical charges, whereas most military ammunition is cylindrical in shape. It is known that in certain directions, cylindrical charges give an enhanced blast close in when compared to that of spherical charges. This paper examines data for cylindrical explosive charges from the literature for Composition B and pentolite and then describes experimental work carried out on cylindrical PE4 charges. Analysis of the free air experimental and literature data shows that close into the curved side of a cylindrical charge it is possible to predict the peak pressure using an equation of the form Peak pressure=K×mass/distance3, where K is an explosive dependent constant; 2695 Pa m3 kg−1 for Composition B, 2498 Pa m3 kg−1 for pentolite and 2565 Pa m3 kg−1 for PE4, for length to diameter ratios of between 2 : 1 and 10 : 1. For a scaled distance (distance/mass1/3) of less than 3.5 m kg−1/3, the results are very accurate. This means that, provided data for cylindrical charges of TNT is obtained, a simple method of determining the TNT equivalency of a cylindrical charge, perpendicular to the curved surface is given by TNT equivalence=Kexplosive/KTNT. For a more accurate prediction at a scaled distance of greater than 3.5 m kg−1/3 a cubic equation of the form Peak pressure=K1Z−3+K2Z−2+K3Z−1 has been found to apply where Z=distance/mass1/3 and the coefficients K1, K2 and K3 depend on the explosive type.