COMPARATIVE INVESTIGATIONS ON BALLISTIC BACKFACE DEFLECTIONS OF COMBAT HELMETS USING FORCE MEASUREMENT AND DIGITAL IMAGE CORRELATION

Abstract

In the present work two different measurement methods are compared for the analysis of ballistic caused “dynamic backface deflections” (BFD): a conservative force measurement and an optical measurement with digital image correlation (DIC). An aramid fibre combat helmet, meeting the requirements of VPAM 3, was analysed with the two methods under the same ballistic conditions (frontal impact, 9 mm x 19 full metal jacket (FMJ); 410 m/s). The force measurement resulted in a cumulative total force of 7.2 kN. A maximum BFD of 22 mm at a maximum speed of 110 m/s was determined using the DIC method. Both methods showed a constant load duration respectively deformation duration of 0.5 ms while the noncontact DIC measurement method resulted in a 120% deeper permanent BFD. Considering the significant limitations of both methods, the force measurement method was evaluated as the more advantageous method for further analysis of realistic, ballistic caused blunt head loads.