Effect of confinement on thick polycarbonate plates impacted by long and AP projectiles

• The resisting force that a PC target can exert on a projectile has an upper limit.
• For high velocity impacts the resisting force may be considered as constant.
• For low velocity impacts, the upper limit of the resisting force is not reached.
• For low velocity impacts the confinement increase the resisting force.

The penetration process in unconfined and confined thick polycarbonate (PC) plates was investigated experimentally and numerically. The confinement was applied by insertion of the PC plate into a conical steel ring. The response of such plates to the impact of long hard steel projectiles, having an ogive-head shape in the range of velocities of 151 < V < 271 [m/s], was investigated experimentally. The results indicate that confinement results in slightly shallower depths of penetrations. Failure parameters which were determined to fit these experimental results served in simulations of these results, and also to those of a 7.62 [mm] AP projectile impacting unconfined PC targets at velocities 600 < V < 900 [m/s]. A very good agreement regarding the trajectory of the projectile was obtained. The resisting force to the penetration depends on the failure strain, whose dependence on triaxiality, temperature and strain rate, should be further investigated. The triaxiality is defined as the ratio: tr = σm/σeq where σm = σii/3 and σeq is the Mises equivalent stress. The numerical results show that the confinement introduces a negative triaxiality within the confined plates prior to impact. The shallower penetration in confined targets is due to the higher negative triaxiality which reduces the ductile damage during penetration, while the hydrostatic pressure reduces the brittle fracture mechanism.