Percorrer por autor "Silva, H."
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- Interlaminar Adhesive Strength of Nano-Reinforced Glass/Epoxy LaminatesPublication . Silva, H.; Ferreira, J. A. M.; Costa, J. D. M.; Capela, C.Interlaminar fracture is significantly influenced by the adhesive strength of fiber/matrix interfaces. Critical strain energy release rate (GC) is the most common parameter used to quantify the interfacial strength. However, subcritical debonding can occur at lower mechanical loads than those required for interlaminar fracture toughness (IFT). This study was performed using nanoclay-reinforced epoxy/glass fiber laminates in order to analyze the influence of the addition of nanoclay and hydro aging on IFT and subcritical crack growth. Hydro aging was done immersinga batch of specimens in distilled water at 25°C for 30 days. Mode I IFT was significantly improved by the incorporation of nanoclays into the resin, the improvement reaching 31% for 3% of nanoclays content. The results of subcritical debonding were plotted in terms of da/dt versus G curves, for dry materials and long term hydro aged composites. Hydro aged composites exhibit not only a reduction of GI c, of about 14% for 3% of nanoclays, but also a higher subcritical crack propagation rate. The addition of nanoparticles reduces subcritical crack propagation rate.
- Mixed Mode interlayer fracture of glass fiber/nano-enhanced epoxy compositesPublication . Silva, H.; Ferreira, J. A. M.; Capela, C.; Richardson, M. O. W.Increasing interlaminar fracture toughness (IFT) has long been an important goal in the fiber reinforced composites field. For that purpose some research has recently explored the use of nanoparticle reinforced matrices to improve interlaminar strength. In this present paper a small quantity of nanoclays (NC) and multiwalled carbon nanotubes (MWCNT) were used in order to enhance the IFT of glass fiber/epoxy composite laminates. The composites sheets were produced by a vacuum molding process. Mode I, Mode II, and Mixed-Mode I/II tests were performed to determine critical strain energy release rates, using double cantilever beam, end-notched flexure, and Mixed-Mode Bending specimens, respectively. Significant improvements in IFT were obtained for all loading modes by the incorporation of NC into the epoxy resin, whilst MWCNT produced only moderate improvements. For Mode I, IFT improvement by the incorporation of nanoparticle fillers, reached about 31% for 3 wt% of NC and 17% for 1 wt% of MWCNT. In Mode II the increase was about 50% for 3 wt% of NC and 30% for 1 wt% of MWCNT. The dispersion of small quantities NC and MWCNT into matrices significantly improved Mixed-Mode IFTs for all loading mode ratios G II/G. The total fracture toughness G increased under Mode II loading components and linear Mixed-Mode fracture criteria reproduced the Gc versus Mode ratios GII/G and GI versus GII relationship.