Fracture-Mechanical Characterization of Fiber Reinforced Plastics in the Crack-Opening-Mode (Mode I)
In view of applications of fiber reinforced plastics at cryogenic temperatures, the mechanical properties of these materials have to be tested both at low temperatures and under various loading conditions (e.g. in tension, compression, shear and in particular in the crack opening mode). The main difficulty with a characterization of the crack growth (mode I) in glass-fiber reinforced materials lies in the fact that the crack length as well as the crack tip cannot be assessed with sufficient accuracy because of delamination and bridging of broken and unbroken fibers. Hence, linear elastic fracture-mechanics cannot be employed. In the present work, first attempts to characterize crack growth in mode I under quasi-static loading conditions in terms of fracture-mechanics have been made. Tests and evaluation procedures based on the fracture-energy-concept, which does not require the knowledge of the exact crack length, have been made at room temperature and at 77 K using a two dimensional glass-fiber reinforced epoxy (ISOVAL 10). Details of the technique as well as results of acoustic-emission investigations and of the influence of sample shape on the fracture-mechanical quantities will be presented. Advantages and disadvantages of the new technique will be discussed.
KeywordsCryogenic Temperature Linear Elastic Material Ligament Length Specific Fracture Energy Starter Notch
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