Issue 29

M. Romano et alii, Frattura ed Integrità Strutturale, 29 (2014) 385-398; DOI: 10.3221/IGF-ESIS.29.34 388 Evaluation of the experimentally obtained results for the velocities of the impactor before and after the penetration according to [21] provides information about the capacity for each single stacking sequence to dissipate kinematic energy. M ATERIALS AND TEST PROCEDURES n the following the used materials and the material processing is described. The used experimental equipment to determine the fibre volume content and the energy dissipation capacity are mentioned. The respective standards (DIN, EN or ISO) are indicated. Materials and processing For the processing of the test panels three different kinds of fabrics and one core material have been used. Tab. 1 contains the fabrics used for the production of test panels and the core material. The tested hexagonal core material is of the kind L ANTOR S ORIC XF [19] with a thickness of approx. 4 mm. It is used as a hexagonal separating layer. This separating layer aims at an enhanced sag of the test panels [6], which should dissipate more energy when penetrated [3]. Three kinds of reinforcement fibres have been used. In each case a twill weave 2/2 has been used as a textile semi- finished product for further processing and building-up the selected layups. In order to achieve a statistically secured amount of comparable specimens five test panels have been produced for each selected layup. Therefore the single fabric reinforced layers have manually been pre-impregnated. This process enables the choice of the selected thermoset resin E PIKOTE R ESIN 04572 [17] as a matrix system for all produced test panels. The curing was done in an autoclave process under a vacuum bag according to the process indicated in the data sheet of the matrix system E PIKOTE R ESIN 04572 [17]. Kind of fibre Type of fabric Spec. weight [g/m²] Warp [1/cm] Fill [1/cm] Literature C arbon twill 2/2 245 6 6 [13] G lass twill 2/2 280 7 6.5 [18] B asalt twill 2/2 345 12 9 [12] Hexagonal Core Mat. - 240 - - [19] Table 1 : Types of fabrics and core material. With these parameters a panel thickness of approx. 4 mm and a fibre volume content of approx. 60 % have been achieved. In order to reach a constant thickness of the test panels the number of single layers in each layup has to be adopted due to the varying thicknesses of the fabrics. Fig. 1 left shows the scheme of the used processing layup considering the vacuum bag in the autoclave curing process. Fig. 1 right shows the corresponding autoclave curing cycle in terms of temperature T in °C, relative pressure p in bar, and relative vacuum in bar over the process time t in min. The geometric dimensions have been selected following DIN 65561 [14]. The German standard requires a final lateral geometry of the specimens of 150 mm x 100 mm. The panels have been built up with a dimension of 210 mm x 160 mm since the edges of the test panels become inhomogeneous and unsteady. The edges have then been cut off by water jet cutting. Specimens for the experimental determination of the fibre volume content f  have been cut of from the cut-off regions near the cutting edge. Their dimensions are approx. 15 mm x 15 mm according to DIN EN ISO 1172 [15] and DIN EN 2564 [16], respectively. Fig. 2 shows schematic the layup and the cutting lines for test panels and the specimen for fibre volume content determination. Tab. 2 lists the investigated types of test panels with their respective labeling, stacking sequence and number of single layers. Thereby five test panels have been produced for every single type, so that 25 specimens have been investigated. There are three kinds of monolithic layups consisting of only carbon, glass and basalt fabric reinforced layers. Additionally there are two kinds of hybrid layups consisting of carbon, glass and basalt. They distinguish from each other by an additionally added hexagonal separating layer L ANTOR S ORIC XF [19] as a core material after the first twelve fabrics or before the last four fabrics, respectively, considering the direction of the later impact. I