Fatigue behavior of vinyl ester polymer and effects of carbon nanofiber reinforcement


Fatigue and cyclic deformation behaviors of vinyl ester and its nanocomposite with 0.5 wt% functionalized carbon nanofiber were obtained by performing tension-tension cyclic tests at different constant stress amplitude levels. Strains were predominantly elastic for both materials, even at high strain amplitudes. There was a small decrease in the cyclic modulus of elasticity of both materials with increasing fatigue cycles, possibly due to the breaking of some polymer chains during the cycling process. Considerable scatter was observed in the fatigue data because of the materials brittleness, necessitating the use of a large number of tests and statistical analysis. Comparisons between vinyl ester and nanocomposite for different probabilities of survival based on log-normal distribution of life showed that the nanocomposite had shorter life than vinyl-ester at higher stress amplitudes, while it had higher life than vinyl ester at lower stress amplitudes. Fracture surfaces observed by SEM consisted of a crack initiation region followed by a smooth region leading to steps or river-like pattern. The fatigue fracture surfaces also contained a series of concentric crack growth bands surrounding the surface source. Cracks initiated subsurface in the nanocomposite specimens and small patches of nanofibers and nanofiber pullouts were observed in the crack initiation area.

Publication Title

12th International Conference on Fracture 2009, ICF-12

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