Penetration force measurement of thin plates by laser doppler anemometry

An experimental method is developed by applying laser-Doppler anemometry (LDA) to measure the velocity history of a projectile impact on a target. The force history was obtained by assuming the projectile to be rigid and by differentiating a polynomial which best fitted the obtained velocity data. This method was then applied to the impact of a hemispherically tipped striker on 1-mm thick aluminum plates. The initial velocity of the projectile ranged from several m/s to 93.5 m/s. When these velocities were low enough not to produce cracks on the plate, double-force peaks were observed in each test, and the value corresponding to the higher peak was proportional to the initial velocity of the projectile. Further, this peak force occurred when the projectile just started to rebound, and spring-back behavior of the plate always occurred. Once the cracks on the target started to form, the peak impact force dropped, and the double-peak phenomenon disappeared. It was also found that the peak force was at approximately the same level for impact speeds above the ballistic limit of the plate. On the other hand, a power law was found to perfectly fit the relationship between the absorbed kinetic energy and the initial velocity of the projectile when it was lower than the ballistic limit.