Schwingbruchstrukturen an faserverstärkten Kunststoffen

Structures of Fatigue Fractures in Fibre-Reinforced Plastics The report deals with macrofractographic and microfractographic structures in non-reinforced epoxide resins as well as in glass-fibre reinforced plastics and carbon-fibre reinforced plastics after fatigue stresses. Epoxide resins show fatigue striations and fracture lines similar to those in metals. The distance between the fatigue striations amounts to between 0.70 and 150 m?m and increases continuously in the direction of fracture propagation. The instantaneous fractures in non-reinforced resin show parabolic cusps besides Wallner-lines and lance-shaped structures. Surfaces of delamination fractures of glass-fibre reinforced plastics show fatigue striations which are characteristic for fibre-reinforced composites, but their morphology differs from the fatigue striations in non-reinforced resin. This was the first time that fatigue striations could be discovered in fibre-reinforced composites of a fibre content of 70 per cent by volume. These fatigue striations are strongly marked at the positions of the fibres and will probably arise only in case of a sufficiently high local stress intensity. Moreover, the amounts of the local slicing and shearing stress components, of which is composed the stress causing the fracture, could be partly responsible for the formation of fatigue striations. The formation of the fatigue striations allows to draw conclusions with respect to the fracture-causing local stress distribution and the local crack propagation in fibre-reinforced plastics. The surfaces of instantaneous fractures in glass-fibre reinforced plastics and carbon-fibre reinforced plastics show parabolic cusps. This is another distinguishing characteristic as compared with the surfaces of fatigue fractures.