Evaluation of Large Amplitude Deceleration Data from Projectile Penetration into Concrete Targets

We examined data from two sets of penetration experiments that recorded deceleration during penetration into concrete targets with compressive strengths of 23 and 39 MPa. The 76.2-mm-diameter, 3.0 caliber-radius-head (CRH), 13 kg projectiles were machined from 4340 Rc 45 steel and contained a single-channel, 15 kHz acceleration data recorder. The data recorder was fitted into a circular hole in the solid nose of the projectile, so during penetration the accelerometer mounted in the data recorder measured structural responses as well as rigid-body projectile deceleration. Since the deceleration data were limited to 15 kHz, higher frequency responses were not measured. Furthermore, there are no available internationally accepted calibration procedures for accelerometers. Because of these complications, we present a method to correct the deceleration data so that an integration of the deceleration data agreed with the measured striking velocity. These corrections were small, and a double integration of the corrected deceleration was in good agreement with the measured depth of penetration. In addition, we developed two empirical penetration models that described deceleration versus displacement and specific kinetic energy (kinetic energy divided by projectile mass) versus displacement for the rigid-body response of the projectile. Data and model predictions showed that the deceleration-displacement response could be closely approximated by a linear rise with a depth of two projectile diameters followed by a region with constant deceleration until the projectile came to rest. Specific kinetic energy-displacement data and model predictions showed a nearly constant slope after the entry region, and this slope is the magnitude of the constant deceleration. Predictions from both methods closely agree with each other and the deceleration data.