Effects of Negative Overpressure Phase of a Laser Breakdown-Induced Blast Wave on Impulse Characteristics

The behavior of a blast wave, in which an initial positive overpressure pulse is followed by a negative overpressure phase, has been investigated mainly by field test using such an explosive as trinitrotoluene (TNT) [1, 2]. The typical pressure history of a blast wave is shown in Fig. 1. The scaled distance Z, which is a function of released energy and distance from the blast wave source, characterizes the positive peak overpressure, Δp+; the duration of positive phase, t+; the negative peak pressure, Δp−; and the duration of negative phase, t−; these values are shown in Fig. 1. For a small Z, the effect of positive phase dominates because of the high Δp+ value. On the other hand, in the range of large Z, the Δp+ value becomes relatively smaller and the negative pressure phase becomes more important. However, it is difficult to evaluate the effect of the negative phase with high-accuracy method because the impulse imparted on an object is sensitive to its size, geometry, and location [3, 4]. Therefore, investigations on negative pressure phase are limited [4, 5] (Fig. 2).