Papers by Author: Jorge M. Antunes

Abstract: The mechanical behaviour of non-chiral multi-walled carbon nanotubes under tensile and bending loading conditions was investigated. For this purpose, a simplified finite element model of armchair and zigzag multi-walled carbon nanotubes, which does not take into account the van der Waals forces acting between layers, was tested in order to evaluate their tensile and bending rigidities, as well as the Young’s modulus. The current numerical simulation results are compared with data reported in the literature. The robustness of the simplified model for evaluation of the Young’s modulus of multi-walled carbon nanotubes is discussed.

Abstract: The study of the mechanical behaviour of single-walled carbon nanotube heterojunctions has been carried out, implementing nanoscale continuum approach. A three-dimensional finite element model is used in order to evaluate the elastic behaviour of cone heterojunctions. It is shown that the bending rigidity of heterojunctions is sensitive to bending conditions. The torsional rigidity does not depend on torsion conditions. Both rigidities of the heterojunction are compared with those of the thinner and thicker constituent nanotubes.

Abstract: In the present study, numerical simulations of nanohardness tests of titanium aluminium nitride (TiAlN) hard coatings with titanium and aluminium ductile interlayers were performed in order to determine the influence of interlayers of ductile metals on the overall mechanical properties of multilayer coatings. The investigation was designed to determine the role of ductile interlayers in altering the hardness value and the Young´s modulus of the multilayer coating as a whole, in comparison with a monolayer TiAlN hard coating, for the cases of composites with different numbers and thicknesses of interlayers.

Abstract: The mechanical behaviour of homogeneous and inhomogeneous FSW aluminium tailored blanks is analysed in this paper. The heterogeneity in mechanical properties across the different weld zones is discussed based on hardness testing results. Tensile and formability test results are also shown and the mechanical behaviour of the welds is discussed in relation to the base materials. Despite the hardness tests have indicated very small differences in hardness, between the welds and the base materials, and the tensile test results also showed similarities in mechanical behaviour, the formability tests revealed additional difficulties in forming the welded sheets.

Abstract: In this work, Si-doped DLC films were deposited on stainless steel (316SS) and polycarbonate (PC) substrates by RF-PACVD in gas mixtures of SiH4+CH4, with 2, 5 and 10 vol.% SiH4. The increase of the Si content in the films led to a progressive drop in the hardness from 30 GPa down to 23 GPa whereas the elastic modulus increased from 124 GPa up to 146 GPa, as measured in the SS coated substrates. In the case of coated PC samples pop-in was observed in the loading curve which was interpreted by finite element simulation and nanoscratching techniques.

Abstract: Depth sensing indentation equipment allows the mechanical properties of thin films to be easily determined, particularly the hardness and Young’s modulus. In order to minimize the influence of the substrate on the measured properties, the indentation depth must be limited to a small fraction of the film’s thickness. However, for very thin films, the determination of the contribution of the substrate and the film to the measured mechanical properties becomes a hard task, because both deform plastically. The numerical simulation of ultramicrohardness tests can be a helpful tool towards better understanding of the influence of the parameters involved in the mechanical characterization of thin films. For this purpose, a three-dimensional numerical simulation home code, HAFILM, was used to simulate ultramicrohardness tests on coated substrates. Materials with different Young’s modulus film/substrate ratios were tested. Analyses of strain and stress distributions for several indentation depth values were performed, in order to clarify the composite behaviour.