Polymer composites group leader, National Bureau of Standards, Gaithersburg, MD
Manager of Composite Research and Development, Hexcel Aerospace, Dublin, CA
Senior scientist, NASA-Langley Research Center, Hampton, VA
Research associate, Hercules Inc., Bacchus Works, Magna, UT
Pages: 21 Published: Jan 1987
A variety of thermoset, toughened-thermoset, and thermoplastic polymers were characterized for Mode I critical strain energy release rates, GIc, and their composites were tested for interlaminar GIcs using the double-cantilever beam specimen. A clear correlation between the data from the two types of experiments was found. With brittle polymers (resin GIcs less than 200 J/m2), the composite GIcs varied from slightly greater than to three times greater than the resin values. Although the resin toughness may represent the lower limit for the composite, the increased GIc value usually found in the composite was attributed to the fiber breakage and pullout that generally accompany composite crack growth. For tough matrix resins, an increase of 3 J/m2 in resin GIc resulted in approximately a 1-J/m2 increase for the composite. This less than complete transfer of toughness was attributed to the fibers restricting the crack-tip deformation zone that is associated with the high GIcs of the polymers. The transition between these two types of behavior occurred at a point where the size of the deformation zone was roughly comparable to the fiber-fiber spacing between plies. Other factors that tended to increase the interlaminar GIc included fiber nesting and bridging, while weak fiber-matrix bonding tended to decrease the crack growth resistance when the poor bonding occurs over extensive areas. This factor is particularly common in thermoplastic composites which exhibited lower interlaminar GIcs than the corresponding thermosets. Scanning electron microscope pictures of the fracture surfaces showed significant regions of failure at or near the interface in the thermoplastic composites.
adhesion, composites, delamination, epoxy, fracture, polyamideimide, polycarbonate, polyethyerimide, polysulfone, toughened epoxy, thermoplastic, thermoset
Paper ID: STP24372S