Diameter effect curve and detonation front curvature measurements for ANFO

Diameter effect and front curvature measurements are reported for rate stick experiments on commercially available prilled ANFO (ammonium-nitrate/fuel-oil) at ambient temperature. The shots were fired in paper tubes so as to provide minimal confinement. Diameters ranged from 77 mm (approximate to failure diameter) to 205 mm, with the tube length being ten diameters in all cases. Each detonation wave shape was fit with an analytic form, from which the local normal velocity D-n, and local total curvature kappa, were generated as a function of radius R, then plotted parametrically to generate a D-n(kappa) function. The observed behavior deviates substantially from that of previous explosives, for which curves for different diameters overlay well for small kappa but diverge for large kappa, and for which kappa increases monotonically with R. For ANFO, we find that D-n(kappa) curves for individual sticks 1) show little or no overlap-with smaller sticks lying to the right of larger ones, 2) exhibit a large velocity deficit with little kappa variation, and 3) reach a peak kappa at an intermediate R.