Abstract
The results of a finite element analysis of the stress induced on the wear surface of a fiber inclined at an acute angle to the counterface are presented. The wear surface produced in the laboratory has revealed that the elliptical wear surface of fibers making an angle of 15-60 deg with the counterface is characterized by cracking of the fibers which liberates wedge-shaped sections of fiber material. The initial crack on the wear surface of the fiber is cup-shaped with the concave side pointing in the sliding direction and primarily occurs in the trailing half of the ellipse. In an effort to explain this behavior, an analysis of the stress on the fiber wear surface resulting from simultaneous frictional loading and contact pressure was conducted. A finite element mesh was created to model a graphite fiber embedded in an epoxy matrix and inclined at 45 deg to the counterface. Frictional stress was simulated by a set of point loads appropriately distributed, acting parallel to the wear surface, and pointing in the sliding direction. The results show that the location and shape of the cracks observed on the experimental specimens coincide with the location and profile of a trace of the stress maxima occurring on the fiber wear surface. The overall highest stress occurs along the major axis of the ellipse which explains observations of partial cracks in the center of some fibers. Furthermore, varying the ratio of frictional stress:contact pressure from 1:6 to 5:6 shows that the location of the stress maxima is independent of the frictional coefficient.