Data processing procedure

Подпись: Fig. 3. Typical incident, reflected and transmitted pulse, [±60]20 IP test, P=0.9 bar

The dynamic compression test conducted in this study consists in placing a cubic sample (13mm in length) between two bars with a high elastic limit, called input bar and output bar. The bar diameter was 20mm. The striker bar was 0.8m long, while the incident bar length was 3m and the transmission bar 2m. These bars are correctly aligned and are able to slide freely on their support. The composite specimen is not attached to the bar in order to prevent the perturbations of measurements due to additional interfaces. The experimental set-up consists of (1) a stress generating system which is comprised of a split Hopkinson bar and the striker, (2) a specimen, (3) a stress measuring system made up of sensors (typically, resistance strain gauges), and (4) a data acquisition and analysis system. The signals are treated with Maple Software using Fast Fourier Transformation to obtain the evolution of the dynamic parameters: stress vs. strain, strain rate vs. time, incident and transmitted load and velocity at the interfaces input bar/sample and output bar/sample vs. time.

The specimens [0]^, [+20]20, [+30]20, [+45]20, [+60]20, [+70]20 and [90]40 were subjected to the in-plane (IP) and out of plane (OP) loading with nine different impact pressures of the striker bar on the input bar: 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.2, 1.4 and 1.6bar. A typical set of incident, reflected, and transmitted signals resulting from gauges A and B recorded by the digital oscilloscope from a SHPB experiment on the composite at the strain rate of 831 s-1 for 60° IP test is shown in figure 3.