END NOTCH FLEXTURE TEST CRACK

The mode-II fracture toughness tended to be constant at 4.5lbf-in/in2 over a range of 5 decades of shear displacement rates. The fracture behavior at low rates indicated transition stick-slip behavior, whereas brittle unstable behavior was evident at higher rates. The delamination resistance indicated constant pattern irrespective of the stroke rates.

END NOTCH FLEXTURE TEST CRACK

The opening mode initiation toughness of T700G/3900 laminate decreased from 3.5lbf-in/in2 to 2lbf-in/in2 and further increased to 3.2lbf-in/in2 over a range of 5 decades of viii crack opening displacement rates. The fracture behavior transitioned from ductile stable to brittle unstable. At higher rates, the resistance decreased gradually. The delamination resistance increased with crack length for the low rate tests. The NB321/7781 laminateвЂ™s opening mode initiation toughness was observed to decrease from 9lbf-in/in2 to 3lbf-in/in2 and further increased to 4lbf-in/in2 over a range of 5 decades of crack opening displacement rates. The fracture behavior was observed to be brittle stable at all rates. The average mode-II fracture toughness of the NB321/7781 laminate was observed to increase from 12lbf-in/in2 to 17lbf-in/in2 over the entire range of 5 decades of shear displacement rates. The tests data indicated ductile stable and brittle unstable behavior with a transition stick-slip behavior. The resistance tended to be constant with crack length for the low rate tests. The average mode-I initiation fracture toughness, GIc of NB321/7781 laminate was observed to decrease with stroke rate from 6.5lbf-in/in2 to 4lbf-in/in2 and further increased to 6lbf-in/in2 over a range of 5 decades of crack opening displacement rates. The rate sensitivities were characterized in terms of the initiation fracture toughness and crack growth resistance. Both N and N laminates were studied in this investigation. Static and dynamic tests, with stroke rates ranging from 8.33Г—10-4in/s to 100in/s, were conducted on double cantilever beam and end notch flexure specimens. The rate sensitivities of mode-I and mode-II fracture toughness, in the form of GIc and GIIc of Toray T800S/3900 carbon unitape/epoxy, T700G/3900 Plain weave carbon fabric/epoxy, and Newport NB321/7781 fiberglass/epoxy materials were investigated experimentally.

End notch flexture test