Thickness effects on fibre-bridged fatigue delamination growth in composites

Abstract

This paper provides an investigation on thickness effects on fibre-bridged fatigue delamination growth (FDG) in composite laminates. A modified Paris relation was employed to interpret experimental fatigue data. The results clearly demonstrated that both thickness and fibre bridging had negligible effects on FDG behaviors. Both energy principles and fractography analysis were subsequently performed to explore the physical reasons of this independence. It was found that the amount of energy release of a given crack growth was not only independent of fibre bridging, but also thickness. Fibre print was the dominant microscopic feature located on fracture surfaces, physically making the same energy dissipation during FDG. Furthermore, the present study provides extra evidence on the importance of using an appropriate similitude parameter in FDG studies. Particularly, the strain energy release rate (SERR) range applied around crack front was demonstrated as an appropriate similitude parameter for fibre-bridged FDG study.

Fibre-bridged fatigue delamination in multidirectional composite laminates

“…(2), has been proposed in a recent study [26]. There is evidence that the application of this new power law relation can result in appropriately interpreting fibre-bridged fatigue delamination behaviors in composite laminates and significantly benefiting one's in-depth understanding on this phenomenon [26,29].…”

“…According to our previous experimental experience in this field [25,26,29], a special test procedure was programed to determine fatigue delamination with different amounts of fibre bridging. DCB specimens were repeatedly tested for several times with different pre-crack lengths, but keeping R-ratio the same.…”

“…(1), is only a phenomenological way to interpret the fatigue data as well as to qualitatively evaluate the significance of fibre bridging [20,26]. According to the energy principles and fractography results [25,26,29], it was reported that fibre bridging indeed had little contribution to permanent energy release in most cases of a fatigue delamination. Particularly, most damage evolution was actually concentrated on crack front regardless of fibre bridging, making the SERR applied on crack front closely related to fatigue crack growth.…”

Fatigue delamination of composite materials – approach to exclude large scale fibre bridging

“…Here one should note that recently Yao et al [23] demonstrated specimen thickness has no significant effect on the zero-bridging curve. This may seem counter intuitive considering the thickness effects reported for quasi-static loading [12] [31].…”

“…Upon manufacturing the laminates for the specimens one has to determine the appropriate thickness, because the thickness has been observed to influence the experimental results [23]. An approximately 12-13 µm thin Teflon or FEP foil should be applied to create the starter crack.…”