E‐glass/DGEBA/m‐PDA single fiber composites: Interface debonding during fiber fracture

Abstract

AbstractIn this paper, we examine the regions of debonding between the fibers and the matrix surrounding fiber breaks formed during single fiber fragmentation tests. The fiber breaks are accompanied by areas of debonding between the matrix and the surface of the fiber. With increasing applied strain, the lengths of these debonded regions generally increase. At the end of the test, the matrix tensile strain adjacent to the debond regions is an order of magnitude higher than the applied strain (40% vs. 4%). Although the debond edges typically remain attached at the same locations on the fiber fragments, debond propagation along fiber fragments under increasing strain has been observed in some cases. The phenomenon is termed secondary debond growth, and two mechanisms that trigger secondary debond region growth have been proposed. As expected, tests with bare fibers and with fibers coated to alter interface adhesion indicate that the average size of debonded regions at the end of the test increases as the calculated interfacial shear strength decreases. However, a decrease in the “apparent” interfacial shear strength resulting from an increase in testing rate results in a decrease in the size of the average debond region. This result suggests an increase in the amount of energy stored in the matrix from the fiber fracture process. POLYM. COMPOS. 28:561–574, 2007. © 2007 Society of Plastics Engineers