Muzzle Exit (Set Forward) Effects on Projectile Dynamics

Abstract

The resulting vibration after the removal of the load would be a free vibration if it were not for material damping, Coulomb damping (friction) at all of the interfaces and joints, aerodynamic drag, and any other damping caused by the cargo or warhead material (fig. 1). In figure 1, we see that during the set back event all of the material, and therefore the center of gravity (C.G.), moves rearward relative to the base when a force is applied to the base. Upon release of this load, the ends of the projectile oscillate about the C.G. Equilibrium position of the C.G. Equilibrium State C.G. moves rearward with compression Accelerating, Axial Force Pressure C.G. back to equilibrium position-structure exhibits damped oscillation about C.G.

Thermomechanical Impact of Polyurethane Potting on Gun Launched Electronics

“…Components are typically designed for the maximum G-force which occurs in the gun tube at around 0.0038 sec. Carlucci et al observed, however, that many electronics components fail during the muzzle exit event, around 0.011 sec in Figure 3 [10]. Contour plots of stress and strain were recorded at 98 increments of the load from Figure 3.…”

“…One drawback of this study is that the viscoelastic model employed is limited to a frequency range that falls below the vibratory frequencies the potted assembly is subjected to during gun launch (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20). Further studies into the highfrequency material behavior are underway to determine the impact on the material behavior and structural stability of the electronic assembly.…”

Comparison of Shock Response Spectrum for Different Gun Tests

“…The two muzzle exit accelerations, set forward and transverse, are higher in the Soft Catch Gun due to impact and interaction with the entrant portion of the catch tube. High-amplitude, muzzle exit accelerations are a known root cause for failures in precision munitions electronic subsystems [19,20]. These muzzle exit accelerations represent risk for the current lot acceptance program.…”

“…Numerous transient dynamic analyses have been completed on electronics subjected to gun launch dynamics, for instance [8,9,[12][13][14]20]. The combined effect of axial and balloting accelerations presents a constantly changing force vector affecting survivability of solder joints, solid state devices, circuit cards and supporting structures.…”

Smart Projectiles: Design Guidelines and Development Process Keys to Success

“…There is an old relation between these thee variables in the gun launch business, which, like Newton's second law and the first law of thermodynamics, has NEVER been disproven. It is as follows Short Schedule + Low Cost = Low Reliability Low Cost + High Reliability = Long Schedule (1) High Reliability + Short Schedule = High Cost…”