MODE-II FRACTURE MECHANISMS OF PET-MODIFIED BRITTLE EPOXIES

Mode II fracture behavior of poly(butylene terephthalate) (PBT)-modifi ed epoxy systems are studied. Two different types of testing for mode II fracture are conducted. One was to investigate the fracture behavio r of bulk epoxy systems, in comparison with mode I fracture, using sin gle-edge notched specimens under skew symmetric four-point loading. Th e other was to investigate the fracture behavior of epoxy layers sandw iched between aluminium adherends using compact shear specimens. The m ode II fracture toughness obtained from the former for modified system s has been found to increase significantly over the control, although the increase of mode I fracture toughness for modified systems over th e control is moderate. This finding is discussed in relation with cavi tation and equivalent mode I stress intensity factor and also in compa rison with rubber-modified epoxy systems in the literature to account for the increase. In addition, the difference in fracture morphology b etween mode I and II is discussed. Mode II fracture toughness obtained from the latter for modified systems has also been found to increase significantly over the control. Morphology of fracture surfaces relati ng to this finding is discussed. (C) 1998 John Wiley & Sons, Inc.