Fracture toughness modelling of fiber reinforced composites by crack resistance curves

Experimental investigations of crack growth kinetics in polymer composites have shown a substantial amount of slow crack growth before crack instability, so that a single parameter like Kc or Gc is not appropriate to characterize the total fracture behavior. For this reason the so-called R-curve concept (crack resistance curve) was used here to describe the failure process. A model is proposed to calculate this function on a micromechanical basis. For this calculation, two dominating processes in the vicinity of the crack tip have to be distinguished. Immediately in front of the notch the creation of a new fracture surface is connected with the consumption of specific energy γ. This material region is termed the process zone. A substantial part of the elastic energy is dissipated in a larger zone near the crack tip-the so-called dissipation zone. The theoretical model is compared to experimental results of short-carbon-fiber-reinforced polyamide.