Giovanna Galtieri

Wear behaviour of UHMWPE reinforced by carbon nanofiller and paraffin oil for joint replacement

The majority of artificial joints incorporate biomedical grade Ultra High Molecular Weight Poly Ethylene (UHMWPE), whose wear is considered most important in controlling service time of the whole joint. The aim of this work was to improve wear resistance of UHMWPE through the addition of 0.5-2.0wt% of Carbon Nano Filler (CNF) and 2% wt of Paraffin Oil (PO) using ball milling (BM) and extrusion techniques (EX). The wear tests on these nanocomposites were conducted by a pin on disc in dry (air) and wet media (simulated synovial fluid or artificial lubricant, and bovine synovial fluid or natural lubricant). Mechanical tests (tensile and hardness), physical analysis (calorimetric, density, wet ability, roughness) and morphological observations were also performed. The experimental results showed that natural lubricant provides the greatest reduction in wear rate while the largest one occurred in air. Furthermore, the BM mixed nanocomposites with a filler load of 1.0% exhibited the best wear resistance among all the samples with an improvement of 42%, 64% and 83% in air, artificial and natural lubricant, respectively. This is due to its higher ductility and thermal features, and lower wet ability in the two lubricants.

Effect of galvanic corrosion on durability of aluminium/steel self-piercing rivet joints

Abstract Galvanic corrosion of steel/aluminium hybrid joints, obtained by self-piercing riveting technique, was investigated. Potentiodynamic polarisation tests, performed in 3·5 wt-% NaCl solution, evidenced the anodic and cathodic behaviour of metal constituent of the joints. Furthermore, long term aging tests were performed to evaluate the relationship among failure mechanism, joint configuration and corrosion damage in salt spray environment. The experimental results evidenced that the degradation phenomena influenced significantly performances and failure mechanisms of the joints, inducing premature failure of the joint at lower stress level at increasing aging time. Furthermore a theoretical model was proposed to forecast failure modes. Based on this model a simplified map of failure mechanisms promoted by corrosion phenomena has been drawn.

How the Use of solvent affects the mechanical behavior of polyester resin/carbon nanotube nanocomposites

Filler dispersion is critical in the nanocomposite feature determination. Physical methods such as sonication are usually employed to disperse carbon nanotubes inside a thermoset polymeric matrix. Those methods often use strong forces to disperse the filler but they could damage it, compromising its reinforcing action. In this paper, we have employed acetone solvent during the sonication process of carbon nanotubes and polyester resin. The solvent helps the carbon nanotube bundle dissolution and favors its homogeneous distribution inside the matrix, thus reducing the action of ultrasounds. Moreover, the carbon nanotubes employed were both pristine and properly oxidized, to favor the opening of carbon nanotube bundles. Solvent was then removed although traces remained in the mixture. We have analyzed the role of solvent during the mixing and the following polymeric network growth. The experimental analyses highlighted as the solvent interacts with the carbon nanotubes during the mixing, thus hindering the right network development. Styrene fragments remain entrapped within the network of polyester resin, softening and improving the adhesive properties. Instead, without solvent, the carbon nanotubes improve the material stiffness in the order CNTox > CNTp.

Three-Point Flexural Properties of Bonded Reinforcement Elements for Pleasure Craft Decks

AbstractThe aim of this work was both to study the performances of pleasure craft reinforced components, bonded using a structural adhesive, and to compare them with those obtained using over-lamination as joining system, typically employed in the shipbuilding. With such aim, two different lots of components were prepared: in the first lot, the reinforcement structures were laminated directly on the investigated composite components and, in the second one; they were made separately in a mould and, then, bonded to the composite components. This last method allowed to evaluate the introduction of a product/process innovation in a field typically unwilling to innovation, still tied to craft, and non-standardized procedures. The results of bending tests, performed in order to evaluate the mechanical behaviour of the reinforced components, evidenced the goodness of this innovative design choice. Finally, a finite element analysis was performed. Graphical AbstractGraphical abstract of the work: Left) Ship 85 feet long; Center) Manufacturing procedures and sections of the reinforcement elements; Right) Test apparatus and typical failure modes