Advanced Materials Forum III

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Authors: S. Gao, Ewald Werner
Abstract: The forging die material, a high strength steel designated W513 is considered in this paper. A fatigue damage model, based on thermodynamics and continuum damage mechanics, is constructed in which both the previous damage and the loading sequence are considered. The unknown material parameters in the model are identified from low cycle fatigue tests. Damage evolution under multi-level fatigue loading is investigated. The results show that the fatigue life is closely related to the loading sequence. The fatigue life of the materials with low fatigue loading first followed by high fatigue loading is longer than that for the reversed loading sequence.
Authors: Ricardo Simões, Júlio C. Viana, Gustavo R. Dias, António M. Cunha
Abstract: The tensile deformation of a semi-crystalline lamellar structure was simulated using coarse-grain molecular dynamics. Interactions between statistical segments are described by Lennard-Jones potentials, with two types of interactions (primary and secondary bonds) defined for the amorphous and crystalline phases. The choice of the correct interaction potentials in coarsegrain simulations requires an understanding of the influence of each interaction potential parameter on the mechanical response. The present paper reports results from that study, following a design of experiments approach. It was found that the apparent modulus is mainly determined by the width of the secondary bond potential. The yield stress and the extent of deformation of the material at a fixed force level are influenced both by the width of the secondary bond potential and the depth of the potential well of the amorphous region. Thus, the tensile mechanical properties and behaviour of the specific lamellar structure under study seems to be mainly determined by the secondary interactions in the amorphous region.
Authors: Stephan Puchegger, Dieter Loidl, Herwig Peterlik, Karl Kromp
Abstract: A novel procedure, based on the Resonant Beam Technique, and its application to anisotropic composites is presented. The evaluation of the elastic modules of anisotropic materials from the measurement of the transverse eigenfrequency spectra of resonant beams is performed by a two step process: firstly the beams cut out from the test material in different directions are evaluated in-dependently of each other under the assumption, that they are isotropic, solving Timoshenko´s equations using an isotropic correction factor for shear. Secondly the beams are evaluated together as representatives of one anisotropic material, using an anisotropic correction factor for shear. The equipment, developed for such measurements is presented. Finally, the procedure is applied to a transversely isotropic carbon fibre-reinforced carbon composite and the relevance of the results is discussed.
Authors: Nuno M.G. Parreira, Nuno J.M. Carvalho, Albano Cavaleiro
Abstract: Tungsten oxynitride films (WOxNy) were deposited with a chemical composition in the range of 0 < x < 1 and 0 < y < 1. For the W-N system, the α-W, β-W, and β-W2N phases were identified according to the amount of nitrogen. In the W-O-N system the structure depended on the amount of oxygen. For an oxygen fraction, fO2 = CO/(CO+CN), smaller than 0.46 the β-W2N phase is evident, whereas above that value the structure became amorphous.
Authors: Olga S. Carneiro, Júlio C. Viana, João M. Nóbrega
Abstract: In this work, a rectangular polypropylene profile was produced with several different extrusion conditions, in order to identify the most relevant processing variables determining its morphology and mechanical properties and to establish relationships between them. A Taguchi Design of Experiments (DOE) technique considering two levels for each variable (extrusion temperature, extrusion throughput, drawdown ratio and distance between the die and the cooling bath) defined the set of extrusions runs carried out. The resulting plastic profiles were characterized in terms of their microstructure and mechanical properties. It was concluded that the most significant processing variable determining the mechanical properties of the profiles is the extrusion temperature and that the drawdown ratio controls the degree of molecular orientation of the profile and, therefore, the extension of its shrinkage after heatiing.
Authors: Ana Vera Machado, Martin van Duin, José A. Covas
Abstract: Dynamic vulcanisation of EPDM/PE blends using the resol/SnCl2 system was studied in a co-rotating twin screw extruder using a series of sampling devices. In order to study the effect of the processing conditions on chemical development along the extruder and on the mechanical properties of the extrudate material, the same recipe (having the same polyolefin/EPDM ratio) was compounded under different processing conditions. The results showed that both chemical evolution and mechanical properties depend on the processing conditions.
Authors: Cristina Borges Correia, João C. Bordado
Abstract: Polyurethane adhesives provide excellent flexibility, impact resistance and durability. Polyurethanes are formed through the reaction of an isocyanate component with polyether or polyester polyols or other active hydrogen compounds. This paper refers to polyurethane adhesives made from polyester polyols with long aliphatic chains (up to 36 carbon atoms) and MDI (diphenylmethane-4,4’-diisocyanate). The polyester polyols have been made from dimer acids obtained from renewable sources and short chain diols. The polyols that were used presented different degrees of unsaturation. The influence of the different raw materials in the adhesives performance is studied. The polyurethanes were produced by reaction between quasi-stoichiometric quantities of polyol and MDI, at several temperatures. The reaction was carried under inert atmosphere and at temperatures below 100°C. Performance of the adhesives was tested by carrying adhesion, hardness and water absorption tests. Characterization of both the polyester polyols and polyurethane adhesives was carried by Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), Magnetic Nuclear Resonance (NMR), X-Ray Diffraction (WAXD), Scanning RMN Imaging of 1H of Stray- Field b (MRI) and Brookfield viscometry.
Authors: Isabel Macedo, Marta C. Oliveira, André Cardoso
Abstract: A study on the impact of batch-to-batch variability of a commercial wet adhesive on its plastic deformation behaviour is here presented. In the chip-apply process, a controlled and stable plastic deformation under thermal-mechanical compression is expected after the first of a two-step curing, named pre-cure. Wet adhesive batches rheological, mechanical and chemical characteristics are available but no information on deformation behaviour is provided. Different pre-curing recipes and oven atmospheres were tested and the plastic deformation was induced by applying pre-defined thermo-compression parameters. Results indicate that shorter pre-cure cycles at higher temperature, under air atmosphere, reduce batch-to-batch deformation variability. DSC curves support these findings. A correlation between deformation level and rheological properties could also be observed, which can be very useful in the triage of adhesive batches for specific process parameters window.
Authors: Jorge M. Silva, Ana Vera Machado, João M. Maia
Abstract: In this work the transient shear behaviour, in terms of both flow and stress relaxation, were measured for several blends of PA6/EPM/EPM-g-MA. The results indicate that there is a competition between slip at the interface due to the non-compatibility between the PA6 and the EPM and the action of the compatibilizer. In flow experiments, at low total strains it was observed that the behaviour is characteristic of immiscible polymer blends and gradually changes to that typical of compatible blends. This suggests that initially the action of the compatibilizer (especially for low compatibilizer contents) is not enough to prevent the lower viscosity PA matrix from slipping around the high viscosity EPM droplets. However, as the droplets are deformed and oriented, the increase in interfacial area enhances the performance of the compatibilizer, thus resulting in a much better interaction between the two phases across the interface.
Authors: Marcin Bilewicz, Júlio C. Viana, António M. Cunha
Abstract: This paper summarizes the processing, morphology and mechanical properties of PP/PCABS blend produced by a non-conventional injection moulding technique: shear controlled orientation in injection moulding, SCORIM. This technique consists on the in-mould shear manipulation of the melt during the solidification phase by using a special mounted mould plate equipped with two external hydraulic pistons. In this work attention is mainly concentrated on the effect of the processing conditions on the mechanical properties of 70/30 (%/w) PP/PC-ABS blend obtained by direct injection moulding. The SCORIM technique was used deliberately to induce a strong anisotropic character of this processed polymer-polymer composite that features a complex morphology, featuring outer highly oriented multi-layers and a less oriented core. Different settings of the operative variables were used according to the moulding program based on a design of experiments array (melt temperature, stroke time, number of strokes), assuring a wide processing window. The fracture surfaces of the mouldings were characterized by scanning electronic microscopy. The mechanical properties were assessed by tensile, flexural and fracture tests. The main significant processing variables determining the mechanical properties of the mouldings were identified together with their effects.

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