Delamination Properties of a Vinyl-Ester/Glass Fibre Composite Toughened by Particulate-Modified Interlayers

Abstract

The main aim of this work is to examine fracture toughness improvement mechanisms of a composite material containing tough interlayers modified with large thermoplastic particles. ¶ Various vinyl-ester (VE)/ poly(acrylonitrile-butadiene-styrene) (ABS) blends were used for the interlayer-toughening of a VE/glass fibre composite to increase delamination resistance of the material under mode I and mode II loading. Dry ABS powder was mixed with the liquid resin in four different weight ratios: 3.5, 7, 11 and 15 phr (parts per hundred parts of resin) while the layer thickness was varied from 150 to 500um. Firstly, the tensile and mode I fracture toughness properties of the VE/ABS blends were assessed, and, by using the Raman Spectroscopy technique, a chemical reaction was discovered which occurred during ABS/VE mixing. This reaction consisted of butadiene dissolution from the ABS particles into the VE. Also, butadiene saturation within the VE was achieved at a composition of around 7% ABS particle content. Both mode I and mode II fracture toughness of the composite were significantly improved with the application of interlayers. Mode I fracture toughness GIc was found to be a function of interlayer thickness and ABS particle content variations, with the latter dominating GIc after the saturation point. Mode II fracture toughness was found to be independent of interlayer thickness and only moderately influenced by particle content. The toughening mechanisms that were the most influential within this interlayered material were plastic deformation and micro-cracking of the layer materials. Evidence of both mechanisms was found using optical and scanning electron microscopy (SEM). ¶ A numerical analysis was conducted, using the experimental results from this study, to further explain the basic toughening mechanisms and fracture behaviour in the materials. The aim of the analysis was to examine the influence of the particles on the plastic zone size that develops in front of the crack tip, and the interaction between the particles and the crack tip. For this purpose FEA elastic-plastic crack propagation models were employed. Good agreement with the experimental data was found. Show more