Coefficient of friction of composite delamination surfaces

The coefficient of friction of delamination surfaces from graphite fiber/epoxy matrix (IM7/8552) composites has been measured in reciprocating sliding. The worn surfaces were examined with a scanning electron microscope and the friction and wear mechanisms were studied. The results show that after an initial wear-in of the surfaces the coefficient of friction will decrease with increasing number of reciprocal cycles as more load is carried by fiber/fiber and fiber/matrix contacts. The evolution of the coefficient of friction is related to whether the starting surfaces are covered with a matrix layer or if the fibers are visible. Any matrix layer will flow to the sides of the contact region, causing fibers to become visible. More of the load will be carried by fiber/fiber and fiber/matrix contacts and the coefficient of friction will decrease. The effective coefficient of friction depends on the amount of load carried by matrix/matrix, fiber/matrix and fiber/fiber contacts and their respective coefficient of friction. Of the three types of contact, the matrix/matrix contact has the highest coefficient of friction, approximately 0.6. Matrix debris formed at the boundary of the contact regions and no wear of the fibers was observed. (C) 2000 Elsevier Science S.A. All rights reserved.