Investigation of failure progress of stitched polymer glass fiber composites
Mateusz Kozioł, Izabella Hyla Politechnika Śląska, Wydział Inżynierii Materiałowej i Metalurgii, Katedra Technologii Stopów Metali i Kompozytów ul. Krasińskiego 8, 40-019 Katowice
Quarterly No. 3, 2005 pages 30-34
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abstract Article presents results of static bending tests of polyester resin-glass fiber laminates specimens: classic and of reinforcing layers stitched with polyaramide thread (Kevlar 50), and recorded simultaneously acoustic emission signal (Figs 2-4). There have occurred clear difference in recorded diagrams for stitched and unstitched laminates. Unstitched specimens have shown much higher amount of acoustic events occurring over period of time in comparison to stitched specimens. These differences can be explained with restricting development of the delamination cracks by stitches in stitched specimens (bridging). Growth of delamination cracks develops gradually with growth of deflection. Restricting simple development of the delamination cracks causes decrease in number of acoustic events recordable during conducted bending test. In order to confirm the predictions related to difference of average delamination crack length of stitched and unstitched specimens, there have been conducted short duration absorbability tests. After 40 minutes long immersion, increase in specimens weight of stitched materials occurred distinctly lesser than those of unstitched (Fig. 5). It confirms the presence of larger delamination cracks in unstitched laminates, because they are undoubtedly the regions penetrated by water during the short duration tests. Difference between stitched and unstitched laminates in average delamination crack length has been observed on a light microscope (Figs 6, 7). Conducted investigations have shown that the registration of acoustic emission signal may be very helpful by analyze of affect of stitching on failure progress of polymer - glass fiber laminates. Key words: stitched laminates, acoustic emission, delamination toughness