Experimental studies on the interaction among cracks, notches and interfaces of bonded polymers

In this paper, we employed simple experimental techniques to investigate a classical yet important failure mechanics problem which has modern applications to the safety and reliability of advanced materials. Polymeric specimens with bonded interfaces and sharp notches were tested in three-point bending. Crack initiation and propagation patterns and loads were documented for validation of numerical simulation techniques. Parameters which were varied include type of material (Plexiglass and Polycarbonate), notch angle (30°, 90° and 120°), interfacial bonding (weak and strong bonds), and loading conditions (symmetrical and unsymmetrical loading relative to the notch tip). Results show that under symmetrical loading, a notch tip connected to an interface causes a mixed-mode crack initiating from the interface. This is in sharp contrast to a mode-I crack initiating from the center of the polymer specimen with any bonded interface as reported in existing literature. Crack propagation occurs along the bonded interface of weakly bonded interfaces, while strongly bonded interfaces show crack kinking into the bulk polymers when the notch angle is greater than 90°. Variations in the loading point in three-point bending lead to corresponding changes in notch/crack tip mode-mixity which significantly influences the crack initiation load. Relationship between the failure patterns and load–displacement curves show the significant influence of notch angle on the crack initiation load.