This thesis is focused on employing the finite element method (FEM) to simulate hot flat rolling process. The relevant work involves selecting a suitable constitutive equation, predicting the rolling load and roll torque, computing temperature changes and lateral deformation, simulating the evolution of substructure, modelling static recrystallisation and designing the rolling pass schedule. A practical pass schedule supplied by an aluminium company and containing reliable measured data of roll load and torque is analysed by a commercial 3-D thermornechanical coupled FEM program FORGE3 V5.3. The inverse analysis method is adopted to obtain the friction coefficient and heat transfer coefficient. The distribution of pressure, equivalent strain, the stress and damage in the roll gap in breakdown rolling are discussed. The changes of temperature and lateral profile under both laboratory and industrial rolling conditions are computed and compared with experimental measurements, the differences are then investigated. Through applying the Taguchi experimental design method, the influence of each rolling parameter on the spread, i. e. the ratio of width to thickness, the roll radius to thickness, the thickness reduction, and the deformation temperature, the relative contribution of each control parameter is quantitatively estimated and expressed as a percentage. A new spread formula is built up based on a large amount of FE analyses. The new formula is able to deal with both laboratory and industrial rolling conditions with high accuracy. Critical reviews are presented for the previous work in the modelling of subgrain size and static recrystallisation. Both empirical and physical models are applied to investigate the evolution of subgrain size, dislocation density, misorientation and the flow stress in the roll gap. The predicted subgrain size agrees very well with the experimental measurement. The difference between the use of two models are illustrated and analysed. Studies on modelling of static recrystallisation are carried out by incorporating the plastomechanical parameters, i. e. strain, strain rate and temperature, into empirical model. Various approaches are proposed to reduce the predicted volume fraction recrystallised at the surface and are verified by the comparison with measurement. Simulation results show that some of the previous work reported in the literature are erroneous. Further work in the modelling of static recrystallisation and texture evolution is detailed. The Taguchi experimental method is also applied to study the influence of the rolling parameters on the fraction recrystallised (Xv ). The study shows that rolling temperature has the greatest influence on the Xv, followed by the parameter H. 1L. The roll temperature and roll speed have little influence on the Xv. Designing a rational rolling pass schedule is critical for the control of strip profile and product quality. In the present thesis, the procedure of designing a rolling pass schedule is illustrated. The formulae used in scheduling are listed and explained. The scheduling program is then performed to check with two existing industrial schedules. The comparison shows that the rolling load, temperature and power model is reliable and shows high accuracy. A multipass simulation by the use of finite element method is also carried out and the results are compared with various model predictions. The problems in the simulation are illustrated and explained.

A 2-dimensional model of a mill roll temperature distribution and radial thermal expansion is presented. The emphasis is on selective axial coolant distribution as a method of controlling strip profile. The Fourier equations describing heat conduction are solved using the method of finite differences. The following effects are considered: (i) The temperature distribution within the roll and strip just prior to entry to the roll bite. (ii) The heat generated in the strip due to deformation. (iii) The heat generated by friction between the strip and the roll. (iv) The temperature distribution of the strip and roll af ter each pass. (v) The heat conducted into the roll when in contact with the strip. (vi) The heat removed from the roll by the coolant, the air and the back-up rolls . The model also takes account of the geometry of the roll. This complexity means that different models for the roll and strip temperature distributions are required. The model evaluates individual heat transfer coefficients along the axis of the roll in order to simulate the effectiveness of each spray zone in removing heat from the roll. A simplified method of evaluating roll thermal cambers, derived from the model, is presented. The model shows good agreement between predicted and measured roll thermal cambers.The model is linked to a strip profile prediction model and used to investigate the effects of changing spray patterns and roll bend on profile. It was found that changing spray pattern has a significant effect on strip profile. It was concluded that: (i) Level spray patterns gave the best shape. (ii) Edge sprays sensitivity is important. (ii) over-cooling outside the strip provides good parabolic shape. ' (iv) A change to exit side, spray levels has a significant effect on strip profile. (v) Exit side sprays only has a tendency of rolling out the middle of the slab (i. e. a flat middle). (vi) All level sprays on the exit side of the roll only produce a distorted profile on the strip. It was also found that for any given change in roll thermal camber, there is a corresponding change in strip profile. The two changes can be related by a linear factor. The value of this factor has been investigated and found to be product and mill dependent.

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A machines surface appears irregular and is recognised as a non stationary random system. Therefore, conventional methods fail to give a precise assessment of the surface profile of a machined component. Very recently fractal methods have been introduced for the surface characterisation of a machines component. Among these methods, the Weierstrass-Mandelbrot (W-M) function is used as an analytical tool to characterise the surface profile due to the fact that it satisfies the mathematical properties of the surface. The successful characterisation depends on a simulation process in which fractal parameters are determined. This work extends fractal conceptual research into an application in the surface characterisation of hardened steel turned components and introduces an iterative algorithmic method of simulation for parametric determination. The method generates an artificial spectrum with fractal features on a computer screen to simulate the real surface obtained from experiment. If the simulated spectrum is statistically similar to that of the experiment, it can represent the real surface profile and the parameters of the W-M function could be used to characterise the surface profile. The work has also investigated the estimation of fractal parameters and how they effect the spectrum. An interactive software package has been developed to implement the simulation which provides both industry and academics with a means of more accurate assessment of surface measurement. Besides the investigation of surface roughness, the residual stress distribution in the superficial layers of a hard-turned component is also investigated using finite element method (FEM). The result shows that the residual stress distribution depends mainly on the initial stress release rather than new stress induction.

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Methods of predicting the dynamic forces are developed for the cases of vehicles negotiating vertical and lateral track irregularities. The bounds of validity of various models of the track are evaluated, from single degree of freedom, lumped parameter models to the case of a two layered beam on elastic foundation with a moving dynamic load. For the case of the lateral response of a vehicle negotiating a track switch, a finite element model of the track is also developed. The vehicle model developed for-the vertical case contains all the rigid body modes of a four axle vehicle for which primary and secondary suspension can be included with viscous or friction suspension damping. Solution of the vehicle/track interaction problem for these non-linear models is obtained by numerical integration, vehicle and track being connected by the non-linear wheel/rail contact stiffness. The most significant forces are shown to arise from the interaction of the unsprung mass and track resilience, with the vehicle modes also making a significant contribution, particularly in friction damped cases. For the lateral case use is made of an existing model of transient vehicle behaviour containing the wheel/rail contact non-linearities, to which track resilience is added in order to predict the track forces. The model is used to predict the forces which would be anticipated at discrete lateral irregularities such as those to be found at track switches. Once again the interaction with the track introduces modes of vibration which are significant in terms of wheel/rail forces. Comparison is made with experimental results obtained from full scale tests in the field. In one experiment the vertical track forces due to a range of vehicles negotiating a series of dipped welds in the track were measured, and in a second the lateral forces were recorded at the site of an artificially introduced lateral kink. A particular application of the results is in the prediction of the rate of deterioration of vertical and lateral geometry due to dynamic forces. This is to offer an improved understanding of the deterioration mechanism in order to influence the future design of vehicles and track to reduce maintenance costs.