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Williams, Jacob

Mechanical Engineering

2021

M.S.

Understanding multi-projectile impact events is important for a wide range of military and aerospace applications. However, experimental studies in this field remain technologically challenging. In this thesis, simulations of two 20 mm caliber projectiles impacting a steel target above the ballistic limit were performed. Peridynamics, a non-local, particle-based computational method, was used to simulate the impacts. The spacing between the two impacts on target was varied to study the effects on projectile residual velocity, projectile deformation, and fragmentation. To optimize the Peridynamic parameters, the simulation results from a single impact were compared to experimental data available in the literature. Methods to track and quantify the kinetic energy, direction, mass, and velocity of individual fragments, including the projectile post impact, were developed. The size of the fragmentation field, the variation of individual fragments, and the residual velocity of the projectile post impact were studied. From the double impact study, we find increased projectile residual velocity, reduced projectile deformation, and greater variation in the fragmentation field with impacts from a second projectile compared to a single impact. It is observed that the increases in projectile residual velocity and reduction in projectile deformation diminish to near first impact levels as the projectile spacing is increased. The projectile is also found to ricochet in closer spacings causing large velocity components normal to the projectile's flight path and reduced damage to the plate. The overall size of the fragmentation field of double impact cases is found to be similar in size to single impacts, however, the number of fragments produced from the impacts are different. In cases where the second projectile impacted closer to the initial impact, only one fragment was formed, while cases with spacing 1.25 calibers and greater produced more fragments than the initial impact. This thesis proved to be successful in employing Peridynamic theory to study complex impact and fragmentation related problems.