Issue 29

M. Romano et alii, Frattura ed Integrità Strutturale, 29 (2014) 385-398; DOI: 10.3221/IGF-ESIS.29.34 394 indicates the capacity of a material to dissipate kinetic energy applied by high-velocity impacts when the material gets penetrated. The experimentally determined fibre volume contents f  vary in a range of 63 % to 57 %. The distinct variation exists even though the same manufacturing process described before as well as the same autoclave curing cycle illustrated in Fig. 1 right has been used. That is the reason why the former described evaluation of the relative dissipated kinetic energy diss,rel E has to be evaluated additionally. In order to standardize the further calculated values based on the nominal values a standardization of the relative dissipated kinetic energy diss,rel E to a constantly presumed fibre volume content f,s  is carried out by calculating   f,s diss,rel, f,s diss,rel f,e E E     (9) where the subscripts s and e indicate the desired standardized value for the fibre volume content and the experimentally determined fibre volume content listed in Tab. 3, respectively. As already mentioned before the autoclave curing cycle was modified in order to achieve a fibre volume content of approx. 60 %. Therefore the presumed fibre volume content for the standardization is selected to f,s 60%   . Results The results are illustrated in terms of the relative dissipated energy of the materials based on the nominal values of the fibre volume content ef,  as well as standardized to the desired value of the fibre volume content %60 sf,   . Because five test panels of each selected layup have been investigated experimentally, the evaluation of the experimental results allows statistically assured results by calculating mean value and standard deviation for each material. As it can later be seen, the standard deviations are generally very low. This is an indicator for constant material quality for all the investigated test panels provided by the manufacturing process as well as for the high reproducibility of the experimental investigations of high-velocity impact loads. Results based on the nominal values of the fibre volume content f,e  Fig. 5 illustrates the relative dissipated kinetic energy diss,rel E for each selected type of layup calculated by Eq. (8) for the three monolithic layups and for the hybrid stacking sequences with and without the hexagonal separating layer. The relative dissipated kinetic energy of the test panels consisting of monolithic layups containing only a single kind of reinforcement fibre, illustrated in Fig. 5, range from 34 % to 44 %. The highest value of the relative dissipated kinetic energy of approx. 44 % is obtained for the test panels built up of only basalt fabrics. The test panels consisting of only glass fabrics dissipated approx. 37 % whereas the test panels containing only carbon fabrics dissipated approx. 34 % of the initial impact energy. The standard deviation is persistently low and lies in a range of 0.85 % to 2.2 %. Thereby the carbon fibre reinforced test panels showed the lowest standard deviation in contrast to the basalt fibre reinforced specimens that showed the highest values of the standard deviation. 33,8% 37,1% 43,6% 34,9% 38,5% 0% 10% 20% 30% 40% 50% 0 1 2 3 4 5 6 Relative dissipated kin. energy E diss,rel Layup configuration Figure 5 : Relative dissipated kinetic energy diss,rel E of the monolithic and hybrid materials based on the absolute values of the fibre volume content f,e  .