PLASTIC ZONE IN FRONT OF A MODE-I CRACK IN ACRYLONITRILE BUTADIENE STYRENE POLYMERS

The shape of the mode I plastic zone observed in the acrylonitrile-butadiene-styrene (ABS) polymeric material is different from that described by the Von Mises or Tresca criterion for yielding in metals. Two distinct, overlapping plastic zones are observed. One has cardioid shape whose through-thickness zone shape is completely different from the dog-bone shape in metals. The other consists of fingers radiating from the crack tip. The cardioid zone is associated with cavitation in the larger rubber particles. The fingers are branching crazes associated with the cavitation inside the small rubber particles. The stress criteria for the formation of these plastic zones are suggested. Also, the way the small rubber particles interact with the crazes to increase the fracture toughness is discussed.