Study of the fatigue delamination behaviour of adhesive joints in carbon fibre reinforced epoxy composites, influence of the period of exposure to saline environment

Abstract

This work analyses the fatigue delamination and fracture stress behaviour under mode I of adhesive joints made on an epoxy matrix composite material with unidirectional carbon fibre reinforcement and a commercial epoxy-based adhesive. DCB type tests (for mode I) were used with the aim to quantify the influence of the period of exposure to a degradation process in a salt spray chamber, to which the tested samples were subjected, on their fatigue behaviour. For this purpose and after a previous static characterisation of the material in which the critical values of the energy release rate for different exposure periods were determined, the levels of the energy release rate to be applied in the fatigue tests and the exposure periods to be considered (no exposure, exposure during one week and twelve weeks) and a ratio of fatigue stress levels of R = Gmin/Gmax = 0.1 were defined. From this experimental data, the G-N fatigue initiation curves and the G-da/dN growth curves were obtained. The experimental data obtained, in the fatigue initiation phase of the delamination process, have been treated by means of a probabilistic model based on a Weibull distribution, the application of models of these characteristics has allowed a better interpretation of the experimental results obtained. The most relevant result of the work is that, in general, the fatigue limits obtained for the adhesive joint, under mode I fracture, when subjected to a degradation process in a saline environment, do not translate into a relevant loss of its resistance capacity against this fatigue delamination phenomenon, in its initiation phase. On the other hand, the crack growth rates of the material subjected to different periods of exposure to a saline environment are similar and higher than those obtained for the material without exposure.

Effect of nano‐silica on fatigue behavior of glass fiber‐reinforced epoxy composite laminates: A Weibull distribution approach

“…4 Numerous researchers have undertaken several studies examining how nanoparticles affect the mechanical properties of composite laminates. [5][6][7][8][9] Nevertheless, when subjected to fatigue loading, the key properties necessary to endure and withstand the conditions are toughness and crack propagation resistance. Nanocomposites composed of silica and polyurethane (SiO 2 /PU) were synthesized by Zhu et al 10 The properties of the electrophoretically prepared membrane modified with SiO 2 /PU exhibited an improvement in terms of strength compared to unmodified and PU-modified laminates.…”

“…It is widely acknowledged that the fatigue strength of these structures is lower than their static strength, primarily due to structural degradation that occurs over repeated fatigue cycles 4 . Numerous researchers have undertaken several studies examining how nanoparticles affect the mechanical properties of composite laminates 5–9 . Nevertheless, when subjected to fatigue loading, the key properties necessary to endure and withstand the conditions are toughness and crack propagation resistance.…”

Mode II Delamination under Static and Fatigue Loading of Adhesive Joints in Composite Materials Exposed to Saline Environment

“…Other research areas in this field involve analyzing the behavior of adhesive joints under different fiber orientations in composite materials [14] and their response to various degradation processes, including humidity, exposure to a saline environment [15,16], freezing and thawing cycles [17], temperature effects [18,19], and the combined effects of temperature and humidity [20].…”