Fatigue behaviour against delamination under mixed-mode I/II and ADCB test of a carbon/epoxy composite material

Abstract

Some composite morphologies are susceptible to loss of capacity due to the presence of interlaminar delaminations. The objective of this work is to experimentally evaluate the generation and propagation of these interlaminar cracks in a carbon-epoxy composite subjected to dynamic stress under mixed fracture mode I / II, using an ADCB type test methodology for this purpose. From a previous static characterization of the material the critical value of the energy release rate was obtained, from which the levels of the critical energy release rate to be applied in the fatigue tests were defined, the values ​​considered were: 45, 50, 55, 60, 65, 70 and 75% Gcr. In all the dynamic tests, an asymmetry coefficient of R = 0.1 was used. From these experimental data the fatigue initiation curves DGN (number of cycles necessary for the nucleation of a crack, for a given rate of energy release) were obtained, observing fatigue life limits of the order of 38% of Gcr . In addition, the crack propagation velocity curves da / dN-G were shown, which showed the trend of the Paris law. On the other hand, a fractographic analysis of the delaminated surfaces was carried out, showing the typical fracture typologies of both modes, I and II, both in the initiation and propagation of the crack, showing the presence of mixed mode I / II in the ADCB type assay.

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