INTERLAMINAR FRACTURE OF COMMINGLED GF PET COMPOSITE LAMINATES/

The Mode I, Mode II and mixed mode (Mode I:II ratios of 4:1, 1:1 and 1 :4) fracture behavior of novel textile glass fiber reinforced polyethy lene terephthalate (GF/PET) laminates has been investigated. The lamin ates were manufactured by compression molding two different fabrics pr oduced by weaving and warp knitting commingled GF/PET yarns. The initi ation fracture toughness of the woven laminates in pure Mode I and Mod e II were slightly higher than those of the warp knitted laminates. Fo r the mixed modes, the difference between the fracture toughness of th e two materials was smaller. An extensive scanning electron microscopy (SEM) investigation of the fracture was conducted to identify any cha racteristic failure mechanisms. The main fractographic features of the Mode I dominated failures were a brittle matrix failure and large amo unts of fiber pull-out. As the Mode II loading component increased, th e amount of fiber pull-out was reduced and the matrix had a more shear ed appearance. A relatively large amount of cusps were found in pure M ode II and mixed mode I:II = 1:4; such features are seldom seen in the rmoplastic matrix composites. A general mixed mode failure criterion, which accounts for the appearance of the fracture surface, was evaluat ed and was seen to give a good fit to the experimental fracture toughn ess values.