Issue 29

M. Romano et alii, Frattura ed Integrità Strutturale, 29 (2014) 385-398; DOI: 10.3221/IGF-ESIS.29.34 392 Resulting values for the fibre volume content f  obtained by the different applied methods The results of the fibre volume content of the single layups are listed in Tab. 3 with its mean values and corresponding standard deviations. The relatively high values of the fibre volume content show high mechanical quality of the material. The relatively low standard deviations represent a high degree of reproducibility of the process at the same time. Experimental setup for high-velocity impact tests In order to carry out and properly evaluate high-velocity impact tests an adequate experimental setup of test equipment is necessary. The experimental setup is schematically shown in Fig. 3 left. It consists of  an instrumented barrel for acceleration of the impactor on the target,  two photoelectric barriers for measuring the velocity of the impactor before the impact,  a test panel mounting where the specimens are inserted and clamped all around with eight bolts M8, each tightened with 5 Nm,  a double exposure instrumentation with the respective high-speed photographic camera for measuring the velocity of the Impactor after penetration of the target and  a bullet screen and a fire case for absorbing the impactor and fragments that have eventually been released. accelerator for sabbots and impactor photoelectric barrier double exposure camera test panel mounting bullet screen fire case vision panel Figure 3 : Schematical illustration of the experimental setup for high-velocity impact tests (left) and high-speed image of the debris after penetration under double exposure (right). The bearing balls are of the steel type 100Cr6. With a diameter of 6.5 mm and the corresponding density of 7.61 g/cm³ the impactors have a mass of 1.12 0.0005  g. Computer numerically controlled (CNC) manufactured plastic sabots were used to accelerate the bearing balls in a barrel. The case on which the plastic sabot is mounted is filled with a special propellant, which was weighted to 0.1 mg precision in order to properly accelerate the impactor in the barrel after ignition. The aforedescribed procedure provides reproducible velocities of the impactor after having left the barrel [21]. On the ballistic flight of the impactor the photoelectric barrier provides the velocity of the impactor before the impact 1 v , the impactor hits the target and after penetration the double exposure with the high-speed camera provides the velocity of the impactor after the penetration 2 v . Fig. 3 right exemplarily shows an image of the high-speed camera after the impactor has penetrated the material. Due to the double exposure the impactor is pictured twice. Knowing the time between the two exposures measuring the distance between the two pictured impactors on the image allows the calculation of the velocity of the impactor after the penetration 2 v . The design of the plastic sabots exhibits four defined slots in longitudinal direction. These slots guarantee the bulking of the plastic sabot after having left the barrel whereas the bearing ball continues its ballistic flight nearly straightly and at constant speed. With the specific design of the plastic sabots the impact of fragments of the plastic sabot in the area of the specimen can be excluded. Fig. 4 left shows the manufactured plastic sabots made of the material POM [20] with the mounted case. Fig. 4 right exemplarily shows a high-speed image of the bulking of the plastic sabot after having left the barrel.