Ferrie W.J. van Hattum

The influence of the dispersion method on the electrical properties of vapor-grown carbon nanofiber/epoxy composites

The influence of the dispersion of vapor-grown carbon nanofibers (VGCNF) on the electrical properties of VGCNF/Epoxy composites has been studied. A homogenous dispersion of the VGCNF does not imply better electrical properties. In fact, it is demonstrated that the most simple of the tested dispersion methods results in higher conductivity, since the presence of well-distributed nanofiber clusters appears to be a key factor for increasing composite conductivity.PACS: 72.80.Tm; 73.63.Fg; 81.05.Qk

Mathematical Models for Particulate Filled and Milled Fibre Reinforced Composites

Due to the low price, low density, good dimensional stability and accuracy, ease and speed of processing, and good workability, liquid epoxy resins are frequently considered ideal materials for manufacturing models and prototype tools of certain complexity. The good mixture capacity with other reinforced materials, in particulate or fibre form, leads to composite materials with intermediate properties that result from the combined action of the constituents. Starting from epoxy based systems suited for high temperatures, different dispersed materials, like aluminium particles, milled carbon and glass fibres were added to the polymeric matrix for Rapid Tooling applications. Aluminium is intended to increase the thermal conductivity of the tool, while the milled fibres improve the wear resistance of the composite tool. In this communication mathematical models for mechanical behaviour of these epoxy matrix composites are discussed. The research is essentially focused on the elastic modulus, because the properties related with the material failure are difficult to analyse due to the complexity of the mechanism that controls the failure of polymer based composite materials. Halpin-Tsai-Nielsen and Halpin-Tsai models were applied to the particulate filled and fibre reinforced epoxy systems, respectively. A critical analysis of the mismatches detected between the experimental and the theoretical values allowed us to propose a semi-empirical model more suited to the results obtained. Parameters related with the particle-matrix and fibre-matrix interface influence the mechanical behaviour of the particulate and milled fibre reinforced composites.

Dispersion of carbon nanotubes in polycarbonate and its effect on the composite properties

The effect of the dispersion state of carbon nanotubes in polycarbonate on the rheological, mechanical and electrical properties of melt-extruded compounds is presented. The dispersion state was monitored by means of grey values distribution histograms of optical micrographs of the composites. Increasing the processing residence time, and hence the deformation induced by the surrounding polymer, increased the level of dispersion of CNTs in the matrix. This, in turn, resulted in a large improvement of the CNTs reinforcement effect and decreased composite electrical resistivity. Rheological behaviour is in agreement with these observations.

A numerical and experimental study of the material properties determining the crushing behaviour of pultruded GFRP profiles under lateral compression

The present work aims at determining the critical material properties that can be used to tailor the crush behaviour of pultruded GFRP (Glass Fibre Reinforced Polymer) box-beams, as can be found in, for example, roadside furniture such as guard-rails. For this purpose, the mechanical behaviour and energy absorption mechanisms of the constituent pultruded box-beam sections subjected to lateral compressive loading, the dominating load case in composite structures when used as roadside furniture, have been studied. The analysed pultruded profiles consist of E-glass fibre reinforcements with two different lay-up configurations in a polyester matrix. The lateral crushing of profile sections is experimentally evaluated and further numerically studied using commercially available tools, applying readily available models incorporated in the software, in analogy to common practice in designing structures, to identify design and material parameters for improving the fracture behaviour of pultruded GFRP profiles. From the analyses, it is shown that the junctions between flanges and webs are the weakest points of box-beam sections: here, high shear stress concentrations in combination with occurring matrix failure lead to further damage such as delamination and tearing. This behaviour is well-described using the Hashin damage model within ABAQUS. Predicted failure behaviour corresponds with observed experimental results, whereas the material stiffness is underestimated. It is shown that the out-of-plane properties (transverse tensile and shear strength) are the dominant parameters affecting the overall performance.

On the Dispersion of Carbon Nanofibre-Based Suspensions in Simple Shear: An Experimental Study

The effect of different dispersion states on the rheological and AC conductivity properties of carbon nanofibre/epoxy suspensions was investigated. Both rheological and electrical properties revealed to be good indicators of the fillers’ dispersion state, as confirmed by optical microscopy. It was shown that imposing a low shear deformation to poorly dispersed suspensions leads to agglomerate rearrangement resulting in a worse dispersion quality and, consequently, lower electrical conductivity. On the other hand, the imposition of a high shear deformation improves the original dispersion, resulting in better electrical conductivity. Rheological observations confirm the trends observed.