Study and redesign of high temperature batch annealing furnace for production of grain oriented electrical steel

Abstract

Grain oriented electrical steel coils are batch annealed at 1200°C to develop the magnetic properties of the strip. Temperature gradients are known to exist within the coils, which can affect the three important reactions occurring in the steel during annealing. These gradients result from the anisotropic conduction properties of the coil and the application of furnace heat. Heat is applied from the furnace to the coil in the radial direction. Studies of the conduction properties of an electrical steel coil have shown that the radial coefficient is ～20% of the axial coefficient. Computational fluid dynamics was employed to simulate a furnace redesign, comprising increased axial heating and a larger coil size. The results show that the annealing cycle time may be shortened and annealing conditions simultaneously improved. The difference between process requirements and process performance can be significantly narrowed by use of the redesigned furnace.     

A novel mathematical procedure to evaluate the effects of surface topography on the interfacial state of stress. Part I: Verification of the method for flat surfaces

A mathematical procedure is developed to utilize the complementary energy method, by minimization, in order to obtain an approximate analytical solution to the 3D stress distributions in bonded interfaces of dissimilar materials. The stress solutions obtained predict the stress jumps at the interfaces, which cannot be captured by current FEA methods. As a novel method, the penalty function is used to enforce the displacement boundary conditions at the interfaces. Furthermore, the mathematical procedure developed enables the integration of different interfacial topographies into the solution procedure. In order to incorporate the effects of surface topography, the interface is expressed as a general surface in Cartesian coordinates, i.e. F (x, y, z) = 0. In this paper, the flat interface problem, i.e. y = 0 surface is considered for verification of the method by comparison with the FEA method. A comparison of the results reveals our new mathematical procedure to be a promising and efficient method for optimizing interface topographies.     

Finite element analysis of steady rolling tyre with slip angle: effect of belt angle

Abstract

The purpose of the present research was to study the effect of different belt angles on the steady state rolling behaviour of a steel belted radial tyre with slip angle. To achieve this goal, a finite element model has been developed using ABAQUS computer software. The simulation started with an axisymmetric model to analyse the tyre under inflation pressure. Then a full 3D model was generated to model the tyre under static vertical load. Having obtained the tyre configuration under contact load, a steady state rolling analysis was conducted using a mixed Lagrangian/Eulerian technique. The final stage of the modelling was the inclusion of the slip angle in the model. Each set of simulations was repeated for three belt angles and the effect of the belt angle variation on the tyre structural variables, including contact pressure and area, lateral force, interlayer shear stress and total strain energy was examined. In addition, the computed value of the number of revolutions per kilometre was compared with experimentally reported data which confirms the accuracy of the present model.     

Numerical modelling for rotational moulding with non-isothermal heating

Abstract

In the rotational moulding process, the internal air temperature has been widely recognised as a tool to predict an optimum cycle time. This paper presents a new numerical approach to predict the internal air temperature in a two-dimensional (2-D) static model without requiring the consideration of the tumbling motion of polymer powder. The initial non-isothermal heating of the static model is actually formed by two changeable plastic beds (stagnant and mixing beds), which represent the actual stagnant and mixing pools inside a rotating mould respectively. In the numerical approach, the lumped-parameter system and coincident node technique are proposed to incorporate with the Galerkin Finite Element Method in order to account for the complex thermal interaction of the internal air. It helps to overcome the difficulty of multidimensional static models in predicting an accurate internal air temperature during the heating stage of rotationally powdery plastic. Importantly, the predicted temperature profiles of the internal air, oven times for different part thicknesses and process conditions accord with the available experimental results.     

Laser welding of copper–nickel alloys: a numerical and experimental analysis

Abstract

Melt run trials were carried out on Cu–Ni bars using a CO₂ laser source in order to analyse the effects of welding parameters (i.e. laser power, welding speed) on geometrical characteristics and on the microstructure of the bead. Experimental results were then used to determine the source parameters to be employed in a finite element model (FEM) of the welding process, with particular attention paid to the thermal field induced by the laser beam. A specific procedure, named 'automatic remeshing technique', was used in order to minimise the computation time. The aim was to create a reliable numerical model, suitable for the optimisation, in practical cases, of welding processes of these kinds of materials. A good correlation, in terms of predicted cooling rates, with the values calculated from SDAS measurements, was observed.     

Error analysis of forward and reverse heat conduction and convection calculations considering uncertainties in welding

Abstract

Numerical models of fusion welding traditionally compute temperature field for a given set of welding conditions in a forward manner. The reliability of computed temperature profile depends on the accuracy of a number of model input parameters, values of which are uncertain in nature. Here, the authors show that a genetic algorithm (GA) assisted integrated numerical model, following either convection or conduction based calculations, can identify the suitable values of the uncertain model input parameters and in turn provide reliable computed results. Powered with GA, the integrated model is used further in a reverse manner to predict multiple sets of welding conditions for a target weld geometry. The convection based calculations have been able to provide more reliable multiple welding variables in reverse calculations.     

Characterisation of mechanical properties of electrochemically deposited thin silver layers

Abstract

In the present work, mechanical properties of electrochemically deposited thin silver layers with known thickness over brass substrates were investigated. For determination of mechanical properties of the layers, a method was used which is novel compared to those traditionally used in practice (in which, for example, a tensile test is carried out on a deposit after removal of the deposited layer from the substrate). The method developed and reported here is a combination of microindentation experimentation and numerical simulations and gives the opportunity to obtain mechanical properties of thin layers without their removal from the substrate. Vickers' microindentation experiment of the silver layer was realized and as a result, led to experimental a load–displacement curve. After that the process of microindentation was modelled numerically by means of finite element method. The numerically obtained load–displacement curve was compared with the experimental one and the result shows good correlation between numerical and experimental curves. For some kinds of layers, which are difficult or impossible to strip away from the substrate, this method reported in this paper is the only one feasible.     

Non-isothermal thermomechanical metallurgical model and its application to welding simulations

Abstract

This paper presents a thermomechanical metallurgical macroscopic model for steels. The model is based on an existing model that is extended for non-isothermal behaviour in combination with phase transformations. The model and its numerical implementation in ABAQUS are described using vector notation for stress and strain tensors. Model parameters are presented for the dual phase steel DP600 and the structural steel S355. For DP600, thermomechanical model parameters, i.e. hardening and strain rate dependency, have been obtained by fitting temperature and strain rate dependent tensile tests. A metallurgical model was implemented using data obtained from phase field models for the austenite growth and continuous cooling transition diagrams for phase transformations from austenite to low temperature phases. The model is applied to welding simulations of DP600 overlap joints and S355 T joints. The final distortion is compared to experiments and it is shown that the model presented is able to reproduce the experimental results very well.     

Numerical simulation of welding-induced distortion in thin-walled structures

Abstract

A sequentially coupled thermal stress analysis approach is presented for modelling temperature and distortion profiles resulting from welding thin-walled structures. The material is modelled as thermo-elastic–plastic with isotropic strain hardening. The heat source is modelled as a three-dimensional (3-D) double ellipsoid, and 3-D finite element (FE) models are employed for predicting ensuing distortions. Comparisons between the simulation results and experiments performed for eight weld configurations are presented. The weld configurations include bead-on-plate, butt weld and tee joint welds with varying plate thicknesses. Temperature measurements using thermocouples and an infrared (IR) imaging radiometer are directly compared to the thermal simulations. Likewise, distortions measured directly on the experimental set-ups are compared to the FE distortion predictions. Very good correlation is obtained for temperature as well as distortion predictions between experimental and proposed numerical approaches. Lastly, details of a weld simulation for the rear section of a motorcycle frame are presented.     

Residual stresses simulation for friction stir welded joint

Abstract

As a solid state joining technique, friction stir welding (FSW) can produce high strength, low distortion joints efficiently. Compared to fusion welding, residual stresses in FSW joints are expected to be low due to a relatively low heat input. However, apart from the heat input, the force from the tool also plays an important role in the development of welding stresses. In the present paper, a semicoupled thermomechanical finite element model containing both thermal load and mechanical load was established to simulate the development of welding stresses during FSW process; an autoadapting heat source model was employed in the thermal analysis; the fixture was also included in the mechanical analysis model. The simulation results showed that due to the effect of the tool force, the longitudinal residual tensile stresses became smaller and were asymmetrically distributed at different sides of the weld centre; the peak of the tensile residual stresses at the retreating side was lower than that at the advancing side. Calculated and experimental results were compared.