Electro-magnetic Tooling for Metal Forming and Powder Compaction

The multipurpose FE Code ANSYS is employed to simulate an electro-magnetic forming process. A complicated compression coil with a ferromagnetic outer screen and a stepped field shaper is considered. Details on FE model building are thoroughly discussed. The calculated parameters are the magnetic flux density around the conductors as well as the Lorentz forces developed in both the field shaper and the workpiece. A simplified analysis of the workpiece deformation characteristics is also provided. An equivalent circuit method is employed in order to validate the results from the electro-magnetic FE model. Results from both analyses are in good agreement, denoting that the FE results are valid from an engineering point of view

Multi-scale simulation of the nano-metric cutting process

Molecular dynamics (MD) simulation and the finite element (FE) method are two popular numerical techniques for the simulation of machining processes. The two methods have their own strengths and limitations. MD simulation can cover the phenomena occurring at nano-metric scale but is limited by the computational cost and capacity, whilst the FE method is suitable for modelling meso- to macro-scale machining and for simulating macro-parameters, such as the temperature in a cutting zone, the stress/strain distribution and cutting forces, etc. With the successful application of multi-scale simulations in many research fields, the application of simulation to the machining processes is emerging, particularly in relation to machined surface generation and integrity formation, i.e. the machined surface roughness, residual stress, micro-hardness, microstructure and fatigue. Based on the quasi-continuum (QC) method, the multi-scale simulation of nano-metric cutting has been proposed. Cutting simulations are performed on single-crystal aluminium to investigate the chip formation, generation and propagation of the material dislocation during the cutting process. In addition, the effect of the tool rake angle on the cutting force and internal stress under the workpiece surface is investigated: The cutting force and internal stress in the workpiece material decrease with the increase of the rake angle. Finally, to ease multi-scale modelling and its simulation steps and to increase their speed, a computationally efficient MATLAB-based programme has been developed, which facilitates the geometrical modelling of cutting, the simulation conditions, the implementation of simulation and the analysis of results within a unified integrated virtual-simulation environment

The mediating effect of environmental policy on the relationship between satisfaction and loyalty in the hotel industry

Customer satisfaction and loyalty, according to the literature, are influenced by many factors such as perceived value, corporate image, perceived quality, trust, communication etc. This study investigates the mediating effect of environmental policy in the relationship between satisfaction and loyalty. For this purpose, empirical research on Greek hotels’ customers, with the use of a structured questionnaire, was conducted. In data analysis, the S.P.S.S 20 and LISREL software were used. The results indicate that the degree of perceived, by customers, environmental policy is not related to satisfaction, and moreover to their loyalty towards the hotel

Drying-mediated patterns in colloid-polymer suspensions

Drying-mediated patterning of colloidal particles is a physical phenomenon that must be understood in inkjet printing technology to obtain crack-free uniform colloidal films. Here we experimentally study the drying-mediated patterns of a model colloid-polymer suspension and specifically observe how the deposit pattern appears after droplet evaporation by varying particle size and polymer concentration. We find that at a high polymer concentration, the ring-like pattern appears in suspensions with large colloids, contrary to suppression of ring formation in suspensions with small colloids thanks to colloidpolymer interactions. We attribute this unexpected reversal behavior to hydrodynamics and size dependence of colloid-polymer interactions. This finding would be very useful in developing control of drying-mediated self-assembly to produce crack-free uniform patterns from colloidal fluids.ope

Spreading and retraction dynamics of sessile evaporating droplets comprising volatile binary mixtures

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Optimisation of the Explosive Compaction Process for Powder-In- Tube MgB 2 Superconductors Using Numerical Simulations

High quality, ex-situ powder-in-tube (PIT) Introduction Nowadays, superconductivity has a significant impact on many technological sectors, for example in the production of electric motors and magnetic sensors as well as in the energy transmission and storage technology. Superconducting wires and tapes are the key product for the adoption of this high technology, but the selection of a suitable superconducting material is not an easy task. MgB 2 is in general a low cost superconductor compared to other ceramic high T c materials, with a transition temperature near the liquid hydrogen boiling point. It has been estimated that approximately 15% of the generated electricity is dissipated during power transportation. In that respect, MgB 2 can be used for the construction of zero loss superconducting transmission lines, where liquid hydrogen may serve as refrigeration medium. The production of wires, coils and tapes requires forming at very high pressures due to the poor formability of the extremely hard ceramic superconductors. For this reason, the powder-in-tube (PIT) explosive compaction technique is considered to be a very promising powder metallurgy forming process for the fabrication of near full density MgB 2 superconductors as given in The present work is concerned with the optimization of the explosive compaction process, incorporating MgB 2 powders. The optimization is performed on an LS-DYNA numerical simulation model of the explosive compaction, where the external diameter of the tube and the dimensions (length and diameter) of the explosive surrounding of the PIT are used as input parameters. The peak pressure, peak maximum principal stress, porosity, uniformity of the tube radius, and mass of the explosive, are the corresponding simulation outputs, with the porosity being the most important parameter to optimize, since it is directly related to the interparticle bonding of the compact which affects the critical current density of the superconductor. Numerical Simulation of Explosively Densified PIT MgB Powders The shock consolidation process of the superconducting powders is numerically simulated using the LSDYNA finite element code. Since the PIT sample deformation during explosive loading is considered to be axisymmetric, a quarter 3D explicit finite element model is developed which is sufficient to accurately simulate the compaction procedure reducing this way the computational time. The finite element model mesh together with the corresponding experimental setup are demonstrated i

Mechanical and thermomechanical characterisation of vacuum-infused thermoplastic- and thermoset-based composites

In this work, a comparative performance study was conducted on glass fibre-reinforced thermoplastic acrylic and thermosetting epoxy laminates produced by vacuum-assisted resin transfer moulding. Mechanical characterisation revealed that the acrylic-based composite had superior transverse tensile strength and mode-I fracture toughness to the epoxy composite, while longitudinal flexural properties and short beam shear strength were found to be comparable. Dissimilar damage evolution behaviour was observed in both materials during tensile testing. The thermomechanical behaviour of the materials has been assessed as a function of temperature. Finally, fractographic investigations of shear and mode-I fracture behaviour revealed distinct fracture mechanisms that complement the findings from mechanical and thermomechanical analyses

Improving the Design of Diamond Wheel for High-Speed Grinding

Grinding at high speeds is a complex process requiring specific tools for successful use. Rotational stresses during high-speed grinding can lead to failure if the wheel is not correctly designed. These results are extremely difficult to be obtained during a large number of field experiments due to the high cost of testing equipment. So, the article describes ways of improving the integrity of the body of the diamond grinding wheel for high-speed regimes using analytical approaches and finite element method