Materials Science Forum Vols. 587-588

Abstract: The use of fibre reinforced plastics – FRP’s – in structures is under a considerable increase. Advantages of their use are related with their low weight, high strength and stiffness. The improvement of the dynamic characteristics has been profitable for aeronautics, automobile, railway, naval and sporting goods industries. Drilling is a widely used machining technique as it is needed to assemble parts in a structure. This is a unique machining process, characterized by the existence of two different mechanisms: extrusion by the drill chisel edge and cutting by the rotating cutting lips. Drilling raises particular problems that can reduce mechanical and fatigue strength of the parts. In this work, quasi-isotropic hybrid laminates with 25% of carbon fibre reinforced plies and 4 mm thickness are produced, tested and drilled. Three different drill geometries are compared. Results considered are the interlaminar fracture toughness in Mode I – GIc –, thrust force during drilling and delamination extent after drilling. A bearing test is performed to evaluate tool influence on the load carrying capacity of the plate. Results consider the influence of drill geometry on delamination. A correlation linking plate damage to bearing test results is presented.

Abstract: Polymers have been known for their flexibility and easy processing into coatings and films, which made them suitable to be applied in a variety of areas and in particular the growing area of organic electronics. The electronic properties of semiconducting polymers made them a serious rival in areas where until now inorganic materials were the most used, such as light emitting diodes or solar cells. Typical polymers can be seen as a network of molecular strands of varied lengths and orientations, with a random distribution of physical and chemical defects which makes them an anisotropic material. To further increase their performance, a better understanding of all aspects related to charge transport and space charge distribution in polymeric materials is required. The process associated with charge transport depends on the properties of the polymer molecules as well as connectivity and texture, and so we adopt a mesoscopic approach to build polymer structures. Changing the potential barrier for charge injection we can introduce holes in the polymer network and, by using a generalised Monte-Carlo method, we can simulate the transport of the injected charge through the polymer layer caused by imposing a voltage between two planar electrodes. Our results show that the way that holes distribute within polymer layer and charge localization in these materials is quite different from the inorganic ones.

Abstract: A special tool-transparent mould designed to visualize the melt flow inside the cavity is used in this research. The aim of the work is to assess the polymer melt behavior under different processing conditions-close to industrial, in conventional and two materials non-conventional injection moulding techniques. The mould is designed with two injection locations and has possibility to change the geometry of the cavity in order to investigate the melt behavior in differently shaped cavities. Visual access in the mould is allowed by the sapphire windows, surrounding the cavity. For image acquisition a high speed video camera NAC 1000 is used. Materials used in the research are three polypropylenes with different flow index. Results are obtained for conventional injection moulding, two material monosandwich and two material biinjection moulding. Apart from visualization, instrumentation of the mould allows to be obtained PT data for each processing condition. Results from conventional injection moulding are compared with MPI5.0 simulations.

Abstract: Laser materials processing has been widely applied in industrial processes due to unique precision and very localized thermal action furnished by the laser’s high energy density and power controllability. With the inherent rapid heating and cooling rates to which this surface layer is subjected, this process provides an opportunity to produce different microstructures from that of the bulk metal leading to useful properties. The aim of this work is to develop a heat transfer mathematical model based on the finite difference method in order to simulate temperature fields in the laser surface remelting process. Convective heat transfer in the remelted pool is taken into account by using the effective thermal conductivity approach. Theoretical predictions furnished by previous models from the literature were used for validation of numerical simulations performed with the proposed model. Experiments of laser surface remelting of Al-9 wt pct Si samples was carried out in the present investigation, and numerical simulations was applied for the laser machine operating parameters. The work also encompasses the analysis of microstructural and microhardness variations throughout the resulting treated and unmolten zones.

Abstract: Polymethylmethacrylate has been used in orthopaedic surgery for the fixation of prosthetic implants for forty years. Cement characteristics, namely rheological and flow properties, greatly affect implant success. Moreover, knowing predictable and reproducible cement flow characteristics allows the surgeon to establish more rigorous handling conditions and prosthesis precise positioning. In contrast to the relatively large amount of work on mechanical properties of bone cements, few data have been published oh their rheological properties. Computational fluid dynamics (CFD) codes using VOF (volume-of-fluid) method has proven to be a useful and robust tool method to simulate multi-material flows with immiscible interfaces. This work explores and describes the possibility of to use a commercial available CFD package (ANSYS CFX®) in the study of PMMA flow on a small dimension multy-channel system.

Abstract: Diffusion bonding is a solid-state welding process that allows the joining of similar or dissimilar heterogeneous materials preventing the weldability problems associated to fusion welding. Modelling of this process has been attempted by several authors like Hill and Wallach [1]. These authors considered that the plastic deformation between two surfaces in contact is one of the most important mechanisms involved in the process. This paper reports the results of diffusion bonding of 1045 steel. Modelling of the process was done using Hill and Wallach [1] parameters to define the surface roughness condition. During preparation for diffusion bonding a series of long parallel ridges, typically with 0.2 to 2 µm high (roughness asperity height) and 30-70 µm width (roughness wavelength) were produced. The initial contact of the asperities on the prepared surfaces created a series of voids with an elliptical shape (infinitely long parallel cylinders with elliptical cross-section). During the diffusion bonding process the shape of the voids changes, becoming smaller, mainly due to the pressure application. Since this is a diffusion controlled process, the use of temperature promotes the deformation process. A model using Finite Element Analysis coupled to a commercial software was developed considering two surfaces, containing an half void, which were brought into contact. The first model was developed with only one elliptical void with two different widths (30 and 70 µm) and 2 µm high. In this model enough pressure was applied to close completely the void. The second model considered three voids placed together to simulate the voids continuity. Finite Element Analysis was developed considering that initial contact between surfaces with asperities creates a series of voids with elliptical shape. In the initial stage of the process, the pressure applied changes the shape of the voids due to plastic deformation increasing the contact area. Microstructures were investigated.

Abstract: The optimisation of sheet metal processes by using numerical simulations has become a key factor to a continuously increasing requirement for time and cost efficiency, for quality improvement and materials saving, in many manufacturing areas such as automotive, aerospace, building, packaging and electronic industries. The introduction of new materials brought new challenges to sheet metal forming processes. The behaviour observed with conventional steels may not be applied when using high-strength steels or aluminium alloys. Numerical codes need to model correctly the material and different constitutive equations must be considered to describe with greater accuracy its behaviour. This enhancement of material description may provide a better prediction of the forming limits, enabling an assessment of the influence of each forming parameter on the necking occurrence and the improvement of press performance. This paper presents two numerical approaches for failure prediction in sheet metal forming operations: one is the implementation of the Lemaitre’s ductile damage model in the Abaqus/Explicit code in accordance with the theory of Continuum Damage Mechanics and the other is the traditional use of FLDs, usually employed as an analysis of the finite element solution in which the necking phenomenon is carried out in the framework of Marciniak-Kuczinsky (M-K) analysis coupled with the conventional theory of plasticity. The previous strategies and corresponding results are compared with two experimental failure cases, in order to test and validate each of these strategies.

Abstract: Alumina and alumina-mullite based refractory ceramic materials were produced from formulations based on an industrial Al-rich sludge derived from the wastewater treatment of the aluminium anodising process. Other ceramic raw materials like diatomite was also added, which can be consider as a by-product. Cylindrical samples processed by uniaxial dry pressing were sintered at different temperatures (between 1400-1650°C, 1 hour soaking) to study the ceramic properties evolution. The performance of fired materials was evaluated (firing shrinkage, water absorption, bending strength, thermal expansion coefficient, refractoriness and SEM microstructure) and demonstrated that optimal properties were obtained at 1650°C for alumina and 1450°C for alumina-mullite.

Abstract: In this study chemical leaching with sulphuric acid has been performed on 10 selected oxidic by-products in order to determine their neutralising capacity. The ultimate aim with this work is to replace the lime or limestone normally used in bioleaching operations to maintain pH at 1.5, the optimum pH-level for bioleaching microorganisms, with oxidic by-products. The investigated by-products includes three ashes from combustion for energy production, five slag samples from ore and scrap based steelmaking, an EAF dust and mesa lime from a paper and pulp industry, slaked lime (Ca(OH)2) was used as reference material. The neutralising potential of the by-products were evaluated by leaching them with sulphuric acid and comparing the amount of acid needed to that of the reference. Most of the by-products examined had good neutralisation potential and some had even higher capacities than Ca(OH)2. Neutralisation kinetics were lower for some slag products due to slow dissolution of some of the silicates present, but kinetics are considered good enough since stirred tank bioleaching is a relatively slow process. Zinc recoveries from the zinc containing materials were high, which thus is an additional benefit if these materials were to be used for neutralisation in a bioleaching process for zinc recovery.

Abstract: Activated carbons (AC) were prepared from waste granulated Polyethyleneterephthalate (PET) by chemical activation with phosphoric acid, sodium hydroxide and potassium hydroxide. All AC were characterised by N2 adsorption at 77 K, and those prepared with H3PO4 had a narrow pore size around 0.8 nm, those prepared with NaOH had a larger pore size higher than 1.52 nm and those prepared with KOH presented a pore size varying between 0.66 and 1.58 nm. The results suggest that H3PO4 and NaOH are not the most suitable activating agents for preparing AC with a high pore volume from waste PET. The AC produced with KOH presented a very high porosity, which passed through a maximum of 0.75 cm3g-1, due to an enlargement of the small micropores with an increase of the carbonisation temperature.