THE FRACTURE ENERGY OF COMPOSITE MATERIALS

A critical analysis of the sources of fracture energy in a composite material showed it to be dependent on the energy of debonding of a single fiber from the matrix material. This energy was measured using a novel technique. A theoretical basis for the fracture energy of a composite was developed relating it to the geometry, debonding energy and frictional force on an individual fiber. It showed that we can expect a more brittle composite if we reduce the fiber diameter, increase the bonding energy, increase the frictional force, or reduce the fiber density in the laminate. These factors appear to be confirmed in actuality. Measurements were also made on the fracture velocity of a crack through resin showing it to be made up of a high velocity region and a low velocity region with substantially similar fracture energies. The actual crack velocity depended on the relative lengths of cracking time at the two different velocities.