INVESTIGATION OF THE FRACTURE-BEHAVIOR OF 3-DIMENSIONALLY REINFORCED COMPOSITES BY ELECTRON SCAN MICROSCOPY

By the use of woven or braided textile preforms it is possible to redu ce manufacturing costs and to improve damage tolerance of composite ma terials due to a three-dimensional fibre reinforcement. An important r equirement for the application of these new technology is a basic unde rstanding of the fracture behaviour because the unique fibre architect ure can cause totally different effects.In an experimental program com posite specimen with 3D woven and braided fibre reinforcement have bee n tested in the special fixture of an electron microscope, allowing th e detection and monitoring of smallest damages (fibre-fracture, matrix -fracture, interphase-fracture, delaminations, notch-growth) and the i nvestigation of damaging effects directly during static and dynamic te sts. The loading condition of the notched and un-notched specimen was three-point bending. The Electron Scan Microscope in combination with the in-situ loading fixture has been prooven to be a very interesting tool to investigate micromechanical damaging effects. It shows that th e 3D reinforcement, especially of the woven material, leads to a signi ficant improvement of damage tolerance resulting for example in a dras tical limitation of notch growth in static and dynamic tests.