Mechanical and fracture performance of carbon fibre reinforced composites with nanoparticle modified matrices

The microstructure and fracture performance of carbon-fibre reinforced polymer (CFRP) composites with an epoxy resin cured with an anhydride hardener containing silica nanoparticles and/or polysiloxane core-shell rubber (CSR) particles was investigated in the current work. Double cantilever beam tests were performed in order to evaluate the fracture energy of the CFRP composites, while the single edge notched bend (SENB) specimen was employed to evaluate the fracture energy of the bulk polymers. Tests were conducted at room temperature and at -80°C. The transferability of the toughness from the bulk polymers to the fibre-composite systems is discussed, with an emphasis on elucidating the toughening mechanism

Thoughts on two approaches for accounting for the scatter in fatigue delamination growth curves

This paper discusses two approaches that have been proposed to account for the data scatter observed in delamination growth tests under cyclic-fatigue loading and thereby enable an estimate of a worst-case delamination growth curve for use in the damage tolerance and durability assessment of composite and adhesively-bonded airframes. The two approaches discussed are: (a) the normalisation approach, whereby the energy release rate is divided by the resistance to delamination growth, GR(a), and (b) the Hartman-Schijve approach to delamination growth. It is shown that for the cases considered this normalisation approach can be used to yield curves that are similar to the ‘mean-3σ’, “worst-case”, i.e. upper-bound, curve obtained using the Hartman-Schijve equation. However, despite the reduction in the scatter that arises if this particular normalisation approach is adopted, there is still considerable scatter in the important “near-threshold” region. In this region the normalised curves are bounded above by the ‘mean-3σ’ curve obtained using the Hartman-Schijve equation. To address this issue, an alternative normalisation approach is then proposed. This alternative normalisation approach has the advantage of having reduced scatter in the near-threshold region but elsewhere is significantly more conservative than the Hartman-Schijve approach

Toughening mechanisms in novel nano-silica epoxy polymers

A crosslinked epoxy polymer has been modified by the addition of nano-silica particles. The particles were introduced via a sol-gel technique which gave a very well dispersed phase of nanosilica particles which were about 20 nm in diameter. The glass transition temperature was unchanged by the addition of the nano-particles, but both the modulus and toughness were increased. The fracture energy increased from 100 J/m2 for the unmodified epoxy to 460 J/m2 for the epoxy with 13 vol% of nano-silica. The microscopy studies showed evidence of debonding of the nano-particles and subsequent plastic void growth of the epoxy polymer. A theoretical model of plastic void growth was used to confirm this mechanism

Characterization Of Epoxy-Coated Oxide Films Using Acoustic Microscopy

An adhesive joint consisting of aluminum adherends bonded with an epoxy adhesive is composed of three main layers. The adherends are usually a few millimeters thick with a layer of epoxy adhesive between one and three hundred microns thick between them. The surfaces of the adherends are typically pre-treated to produce a thin film of porous aluminum oxide, which has a honeycomb-like structure. The epoxy adhesive may then penetrate into these honeycomb cells or pores. The resulting layer between the adhesive and adherend is therefore a micro-composite and it is typically of the order of one micron in thickness. The use of the surface pre-treatment is a major factor in increasing the durability of the adhesive joint when it is exposed to water. Additionally, joints which have been in use for some time, especially ones which have been subject to environmental attack, usually experience a failure along the plane of this film. Therefore, characterization of this epoxy/oxide interlayer is very important in understanding adhesive joints and how they are affected by environmental factors. Unfortunately, not much is known about their mechanical properties