On delamination threshold loads in low velocity impact on glass-carbon/epoxy composites
Krystyna Imielińska*, Rafał Wojtyra**, Marek Kozłowski*** *Politechnika Gdańska, Wydział Mechaniczny, Katedra Inżynierii Materiałowej, ul. Narutowicza 11/12, 80-952 Gdańsk **Politechnika Gdańska, Wydział Oceanotechniki i Okrętownictwa, Katedra Technik Głębinowych, ul. Narutowicza 11/12, 80-952 Gdańsk ***Politechnika Wrocławska, Instytut Inżynierii Ochrony Środowiska, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław
Quarterly No. 1, 2005 pages 69-74
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abstract When a structure is accidentally impacted by an object, (e.g. by dropping a tool) it may be important to know if the impact is likely to cause serious damage in the structure. The easiest way to solve this is to compare the impact energy with the threshold impact energy of the structure. Thus, it is necessary to find the threshold impact energy of the structure which depends on the properties of the material and boundary conditions. In the present work the problem of delamination threshold load assessment was studied for epoxy laminates reinforced with woven glass-carbon laminates. The behaviour of symmetrical and unsymmetrical glass E/carbon C laminate was studied (E/C/E/C/E and E/E/C/E/C). Instrumented impact and static indentation tests were used. The rebound impact tests were conducted on the 100 mm square specimens in standard instrumented dropping weight tower Ceast Dartester. Indentation tests were performed using the same samples and supports geometry as in impact tests. The acoustic signal was used to assess the load and deflection corresponding to the first damage in the laminate. Damaged samples were examined using SEM. The approximate projected maximum delamination area was assessed and plotted against impact energy and maximum load (Fig. 6). The experimental results obtained in this work show (Figs 5, 6) that, similar to quasi-isotropic fibre reinforcement, for woven glass/carbon/epoxy laminates there exists a threshold impact load corresponding to a sudden jump of the area of delaminations from zero to a certain value (100 mm2). The threshold impact energy was found 1.5 J independent of the glass fibre stacking sequence. The near-thethreshold damage in woven glass-carbon/epoxy laminates consists of delaminations and fibre/matrix debonding. Good correlation of the projected damage area obtained in this work for static (indentation) and impact measurements confirm that prediction of the threshold impact damage by quasi static tests instead of instrumented impact test is practical and useful. Key words: laminates, impact resistance, polymer composites