|M.Sc Student||Weiss Alon|
|Subject||Experimental Investigation of Projectile Penetration|
Resisting Force in Polycarbonate Targets
|Department||Department of Aerospace Engineering||Supervisor||Professor Emeritus David Durban|
The earliest recorded studies on terminal ballistics date back to eighteenth century ideas by Euler and Robins who argued that projectile resisting force remains constant during the penetration process. Later work by Poncelet (1829), Resal (1895) and Petry (1910) has paved the way to modern penetration science and engineering in deriving velocity dependent formulae for resisting force.
This work presents a comprehensive experimental and analytical observation on polycarbonate ballistic response. Deep penetration and plate perforation tests were conducted with several thicknesses of polycarbonate targets at normal impact and within striking velocity range of 500-900 m/sec. Projectile penetration location, velocity and acceleration, were monitored using high-speed cameras for tracking the depth of penetration path and orientation.
One of the primary objectives of this work was to examine the possibility of a simple constitutive equation to predict the depth of penetration for rigid projectiles into polycarbonate targets. Experimental results have confirmed the original hypothesis of Euler that the resisting force during penetration is nearly constant. This observation is based on a wide range of test data with ogive head armor piercing projectiles.
Following the standard approach of steady state cavity expansion, cavitation fields in spherical and cylindrical configurations are derived and applied to predict the specific cavitation energy for polycarbonate targets. The specific cavitation energy, identified with the cavitation pressure, can be used for estimating the penetration depth and the ballistic limit of protective plates in which ductile hole formation is the dominant mode of failure.
It is suggested that not all of the projectile kinetic energy converts to plastic deformation energy, part of the projectile energy is diverted to the cracking process within the layer adjacent to the projectile. We obtain formulae for the cavitation pressure that apply for assessment of resisting stress during projectile ballistic penetration. We found that the spherical cavitation pressure in presence of damaged zones is in satisfactory agreement with test data. Material response is modeled as elastic/perfectly-plastic of Mises type with neglect of elastic compressibility. Sensitivity to failure strain is examined and useful closed form formulae are derived.