Discussion on the use of the strain energy release rate for fatigue delamination characterization

This paper discusses the use of the strain energy release rate (SERR) as a parameter to characterize fatigue delamination growth in composite materials. Based on the observed difference in fatigue delamination response, it is argued that the fibre bridging generated during quasi-static and fatigue loading is significantly different and normalization of fatigue data with quasi-static SERR becomes meaningless. From the physical view, bridging fibres should not impose any strain energy release during fatigue delamination, unless they fail. This is supported by analyzing the earlier mentioned experiments with an energy approach. When the measured strain energy release normalized against the applied number of cycles is plotted against the fatigue delamination growth rate, all data approximately coincides to a single curve. It is therefore concluded that the current use of SERR to characterize fatigue delamination growth is not in agreement with the physical concept of strain energy release.