The mechanical properties of processed metal depend greatly on the micro-structural changes durin... more The mechanical properties of processed metal depend greatly on the micro-structural changes during the extrusion process. A clear theoretical concept of the thermodynamics and tribology of the metal extrusion process with respect to the major process parameters, namely tem- perature and strain rates are necessary to decide the optimum values of machine settings. This paper discusses the essential theoretical understanding of the process of metal extrusion, including the effects of die geometry, flow pattern and other variables with the help of the �nite element program ABAQUS.
The goal is to build up an inverse model capable of nding the average grain size history dur- ing... more The goal is to build up an inverse model capable of nding the average grain size history dur- ing an extrusion process and other material constants by using simulated strain and temperature values. This problem of nding the parameter values is based on linear and nonlinear least-squares regressions, cou- pled with microstructure control models and the so- lution of a nite element extrusion model. The prob- lem is ill posed and we use the Tikhonov's regulari- sation to stabilise the solution process. Further some of the parameters in the model are linear and some are nonlinear. We determine the linear parameters using simple linear algebra and for the computation of non-linear parameters we use MATLAB's routine lsqnonlin.
This paper investigates a technique to nd an optimal set of conditions for an isothermal process ... more This paper investigates a technique to nd an optimal set of conditions for an isothermal process to extrude a product for a given shape and material properties with minimal defects. The inputs to this model are: the product geometry and its mate- rial data such as o w curve and microstructure during dynamic recrystallization. This is an inverse problem and the model is formulated as a non-linear least- squares minimization problem coupled with a nite element model for the extrusion process. It is done by constructing an iterative procedure using an op- timisation routine such as MATLAB's lsqnonlin and at each iteration, the extrusion o w is solved using ABAQUS. First all control points of a Bezier-curve for the die surface that minimizes the redundant strain inside the deformation zone are found. Then the ini- tial billet temperature, die temperature and the ram speed that closely match with the strain rates and temperatures for the desired microstructure (grain size) are obtai...
International Journal of Modelling, Identification and Control, 2007
... 1 An appropriate local bond-slip model considering the behaviour characteristics in the bond ... more ... 1 An appropriate local bond-slip model considering the behaviour characteristics in the bond between the aerated concrete and galvanised steel. ... The load-displacement (P − d) behaviour of the bonding on flat surfaces can be determined normally by conducting pure shear pull ...
ABSTRACT This paper is dedicated to an impregnation technique for crack identification of uniaxia... more ABSTRACT This paper is dedicated to an impregnation technique for crack identification of uniaxial tensile behaviour of concrete samples. A method for crack identification in concrete after uniaxial tension tests was adopted for the observation of differences between various experiments which were conducted with and without the elimination of secondary flexure. During the procedure an epoxy resin containing fluorescent dye was infused into concrete samples by vacuum to expose cracks and defects. After impregnation the samples were sawed from the prism and pictures taken under ultraviolet light.
The mechanical properties of processed metal depend greatly on the micro-structural changes durin... more The mechanical properties of processed metal depend greatly on the micro-structural changes during the extrusion process. A clear theoretical concept of the thermodynamics and tribology of the metal extrusion process with respect to the major process parameters, namely tem- perature and strain rates are necessary to decide the optimum values of machine settings. This paper discusses the essential theoretical understanding of the process of metal extrusion, including the effects of die geometry, flow pattern and other variables with the help of the �nite element program ABAQUS.
The goal is to build up an inverse model capable of nding the average grain size history dur- ing... more The goal is to build up an inverse model capable of nding the average grain size history dur- ing an extrusion process and other material constants by using simulated strain and temperature values. This problem of nding the parameter values is based on linear and nonlinear least-squares regressions, cou- pled with microstructure control models and the so- lution of a nite element extrusion model. The prob- lem is ill posed and we use the Tikhonov's regulari- sation to stabilise the solution process. Further some of the parameters in the model are linear and some are nonlinear. We determine the linear parameters using simple linear algebra and for the computation of non-linear parameters we use MATLAB's routine lsqnonlin.
This paper investigates a technique to nd an optimal set of conditions for an isothermal process ... more This paper investigates a technique to nd an optimal set of conditions for an isothermal process to extrude a product for a given shape and material properties with minimal defects. The inputs to this model are: the product geometry and its mate- rial data such as o w curve and microstructure during dynamic recrystallization. This is an inverse problem and the model is formulated as a non-linear least- squares minimization problem coupled with a nite element model for the extrusion process. It is done by constructing an iterative procedure using an op- timisation routine such as MATLAB's lsqnonlin and at each iteration, the extrusion o w is solved using ABAQUS. First all control points of a Bezier-curve for the die surface that minimizes the redundant strain inside the deformation zone are found. Then the ini- tial billet temperature, die temperature and the ram speed that closely match with the strain rates and temperatures for the desired microstructure (grain size) are obtai...
International Journal of Modelling, Identification and Control, 2007
... 1 An appropriate local bond-slip model considering the behaviour characteristics in the bond ... more ... 1 An appropriate local bond-slip model considering the behaviour characteristics in the bond between the aerated concrete and galvanised steel. ... The load-displacement (P − d) behaviour of the bonding on flat surfaces can be determined normally by conducting pure shear pull ...
ABSTRACT This paper is dedicated to an impregnation technique for crack identification of uniaxia... more ABSTRACT This paper is dedicated to an impregnation technique for crack identification of uniaxial tensile behaviour of concrete samples. A method for crack identification in concrete after uniaxial tension tests was adopted for the observation of differences between various experiments which were conducted with and without the elimination of secondary flexure. During the procedure an epoxy resin containing fluorescent dye was infused into concrete samples by vacuum to expose cracks and defects. After impregnation the samples were sawed from the prism and pictures taken under ultraviolet light.
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