Falling Weight Impact and Indentation Damage Characterisation of Sandwich Panels for Marine Applications

On three configurations of laminates for nautical use, impact and indentation properties have been compared, in the understanding that these represent two different and significant cases in the laminate service, namely contact with fal- ling body and ramming. All the laminate configurations were fabricated using the same stacking sequence of E-glass mats (of weight 225 and 600 g/m²) as skins, while the core was obtained with different types of rigid PVC foams in the case of A laminate (HEREX C-75) and in that of B and C laminates (COLTH C-55). The latter laminates are also protected with Gelcoat on the outer side. The resin used for A and B laminates was a conventional vynilester (DISTITRON VE 100 SC), while for C laminate a polyester-based including some non-oil derived components was used (ENVIREZ 1807). Laminates of each of the three configurations have been impacted from 1, 1.5 and 2 meters with a 1.25 kg mass using a 12.7 mm hemispherical nose, therefore yielding impact energies of 12.25, 18.37 and 24.5 Joules respectively. Subsequently, other laminates have been quasi-statically indented at with 0.05 mm/s cross-head speed, using the same indentor, until the maximum average displacement obtained during low velocity impact for each configuration and each energy was obtained. The results obtained show that strain rate has an effect on the performance of these laminates. In particular, the improved resistance to penetration appears to occur at the expense of damage dissipation due to vibrations. Quasi-static indentation does not appear to fully reproduce the effect of low velocity impact loading for these sandwich structures, showing significant differences in the hysteresis cycles, both during loading and during the damping phase, which need to be combined with the variable effect of damage on the laminates.