Study of the phenomenon of fatigue delamination in a carbon-epoxy composite under mixed mode I/II fracture employing an asymmetric specimen

Abstract

The onset and growth of interlaminar cracks (delamination) were experimentally studied in an IM7/MTM45 carbon-epoxy composite material under mixed mode I/II dynamic loading, with a mixity grade GII/G of 0.24, employing for this purpose an asymmetric specimen.Static tests were previously carried out to obtain the critical fracture properties of the material. The dynamic test strategy was defined using these data. This consisted in the application of different fixed percentages of the critical ERR, Gcr. The results enabled the determination of crack onset fatigue curves, ΔG -N (number of cycles before crack onset, for a given ERR). A fatigue limit value of 38% Gcr has been obtained, understanding as such the ERR necessary for the onset of delamination. Delamination growth rates were shown to fit a Paris law trend with average crack growth rates of 10−4 mm/cycle. The fractographic analysis carried out on the tested specimens confirmed the presence of mode I and II fracture typologies, as well as evidencing the progression of micro-cracks due to fatigue.