Fracture Mechanics Analysis of the Single-Fiber Pull-Out Test and the Microbond Test Including The Effects of Friction and Thermal Stresses

The energy release rate for propagation of a debond in either a single-fiber pull-out test or a microbond test was derived analytically. The key finding was that an accurate analysis can be derived by a global energy analysis that includes effects of residual stresses and interfacial friction but does not need to include the details of the stress state at the interfacial crack tip. The analytical results were verified by comparison to finite element analyses. The energy release rate expressions were used to determine interfacial fracture toughness from singlefiber pull-out tests or microbond tests. The experiments included both macrosized model microbond specimens (steel wire/epoxy) and micro-sized pull-out and microbond specimens (glass fiber/epoxy or vinyl ester). In all experiments, it was critical to correctly account for the true level of residual stresses in the specimen; it some experiments, the inclusion of friction was also critical. For experiments involving physical aging conditions, it was essential to additionally account for partial relaxation of internal stresses.