Statistical Comparisons Between Qualification Tests for Gun-Fired Projectiles

Abstract

The U.S. Army uses several types of tests to increase the reliability of gun-fired munitions. Systems, subsystems, and components are gun fired to assess reliability. When failures are found, root-cause investigations are completed and parts may be redesigned. For instance, the 155 mm projectile Excalibur uses several types of tests to find failures and build reliability. Components are tested in a rail gun, a new soft-catch gun, and in soft recovery vehicles. With the rail gun, test projectiles are fired from a worn gun tube into a trough of water. The soft-catch gun, a hybrid system using both air and water, has a standard cannon tube and a series of catch tubes to stop a projectile. The third type of test, a soft recovery vehicle, uses a modified tactical Excalibur with a parachute for a soft landing. All three types of tests have on-board recorders to capture ballistic accelerations. Accelerometer data are used in failure investigations, redesign parts, and to design new projectiles. The purpose of this paper is to compare accelerations from different types of ballistic tests. Comparisons were done to determine if the tests were in the same statistical family. Comparisons are made for a United States MACS 5 charge. The maximum axial forces were the same for the soft-catch gun and the soft recovery vehicle. In the balloting directions, the rail gun and soft recovery vehicle had similar forces. The set forward forces differed in all three cases, reflecting the different catch mechanisms for the projectiles. Comparisons of g-forces were also made using shock response spectra. The shock response indicated that the damage potential is greatest for the rail gun tests, consistent with an increase rate of failures for some electronics.

Comparison of Shock Response Spectrum for Different Gun Tests

“…1, consists of a tactical 155 mm gun tube and a contiguous series of catch tubes designed to bring the projectile to a stop without damage. Although the muzzle exit accelerations are higher with the Soft Catch Gun, failures, when they occur, are similar to those observed in tactical tests [1]. The failure rates are higher using the Soft Catch Gun which provides additional margin data and even some cost savings.…”

“…Acceleration and pressure data are recorded using on-board recorders. Reference [1] describes the details of the on-board recorders primarily used with the Soft Catch Gun. The location of the on-board recorder is near the IMU's tactical location, Fig.…”

“…For the n = 9 near-tactical shots at MACS 5, the 95/50 NTL was 1.71; for the n = 10 soft catch shots at MACS 5, the 95/50 Normal Tolerance Factor was 1.7. Table 1 contains updated statistical comparisons between MACS 5 charge data for the Soft Catch Gun and data gathered during near-tactical round testing at Yuma Proving Ground [1]. This data was determined from the asrecorded, acceleration versus time history.…”

“…When failures occur, they are investigated, root cause is determined and improvements are made. Most of these tests are instrumented with pressure gages, accelerometers or both [1][2][3][4][5][6][7]. Accelerometer data is reviewed for trends, used for failure reviews, and utilized in design and redesign of components [8][9][10][11][12][13][14].…”

Shock mitigation for electronic boards within a projectile

“…Amy et al [11] reviewed and compared methods for predicting the reliability of electronic equipment. Cordes et al [12] compared accelerations measured during different types of ballistic tests to determine if the tests were in the same statistical family. Comparisons of g-forces were also made using shock response spectra.…”