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 (» 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 k, were generated as a function of radius R, then plotted parametrically to generate a D n (k) function. The observed behavior deviates substantially from that of previous explosives, for which curves for different diameters overlay well for small k but diverge for large k, and for which k increases monotonically with R. For ANFO, we find that D n (k) curves for individual sticks 1) show little or no overlap¾with smaller sticks lying to the right of larger ones, 2) exhibit a large velocity deficit with little k variation, and 3) reach a peak k at an intermediate R.Near critical diameter, ANFO exhibits a severe velocity deficit; however, with increasing diameter a slight upturn in the diameter effect curve is observed. We developed an extension of the widely used Campbell/Engelke (3) curve fit that accurately captures both behaviors together. INTRODUCTIONRate stick tests on lightly confined prilled ANFO at ambient temperature were conducted to measure steady-state detonation velocity and detonation front curvature as a function of diameter. It is well known that ANFO's detonation velocity varies considerably with charge diameter. Yancik (1) , Petes (2) , and others have shown that several other physical properties can affect ANFO's detonation velocity. These include the type of confinement, explosive density, particle size and distribution, fuel oil content, moisture content and temperature. Furthermore, these factors can be interdependent. Differences in detonation velocity can also be attributed to slightly different physical properties of the ammonium nitrate (AN) produced by different manufacturers. Because there are no standard specifications by which AN is produced, batch-to-batch variation from a single production plant is not uncommon. Although performance data for ANFO have been studied for over four decades and become somewhat self-consistent since being introduced in the mid-1950's, variability in performance can still be expected from this highly non-ideal explosive.

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