On the Low Endurance Fatigue of Rubber-Toughened Adhesives and Its Implication on Characterization of Damage

A high sensitivity test method has been developed for axial strain con trolled fatigue testing of flat sheet specimens. The low strain fatigue behaviour of a high performance epoxy film adhesive (FM73) and a cast lab-made rubber-toughened epoxy resin has been established over a specified range of applied total strain amplitude. This has aided the characterization of damage evolution and the determination of related cyclic and monotonic stress/strain properties. Experimental results have indicated that the cyclic behaviour of these materials can be described by an equation similar to the Coffin-Manson law. The value of the fatigue ductility exponent was found to be within the range reported for other polymeric materials. Moreover, the load history and the hysteresis loops obtained at different strain levels reveal the damage mechanisms in these materials. Examination of the fatigue surfaces using scanning electron microscopy showed that microvoiding, particle/interface debonding, particle cavitation, fatigue striation and microcracking were the main sources of damage under cyclic loading.