Towards Understanding Fatigue Disbond Growth via Cyclic Strain Energy

The concept of relating fatigue disbond growth to the strain energy release rate (SERR) is critically examined. It is highlighted that the common practise of using only the maximum SERR or only the SERR range is insufficient to correctly characterize a load cycle. As crack growth requires energy, it is argued that growth should be related to the total amount of energy released during a fatigue cycle, and not to the amount of energy that would be released by a crack growth increment under the instantaneous load conditions at one point in the load cycle. This argument is supported by experimental evidence, showing that the relationship between fatigue disbond growth (FDG) rate and either maximum SERR or SERR range is R-ratio dependent, whereas the relationship between FDG rate and the loss of strain energy is not.