Miljenko Math
University of Zagreb
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Featured researches published by Miljenko Math.
Journal of Materials Processing Technology | 2002
Miljenko Math; Branko Grizelj
Abstract In order to determine the inevitable mechanical springback of bent plates, designed for assembling spherical tanks made of steel StE 500, according to DIN 17102/83, an elastic–plastic incremental finite element calculation has been carried out to analyse axisymmetric strain in a sheet metal bending process. Sufficiently accurate stress distributions and deformed geometry of plates as parts of spherical tanks have been carried out through the whole bending process. The load–deflection curve has been carried out based on reaction forces and compared with experimentally obtained results. Friction effects and material characteristics such as work hardening are also covered. The accuracy of the simulation results, mechanical springback and the residual stress distribution after unloading are discussed through the comparison to the experimental results.
Key Engineering Materials | 2007
Branko Grizelj; Branimir Barišić; Miljenko Math
The paper is concerned with the numerical method of determination bending force and calibration force in plate bending. For numeric procedure the finite element method is used. Calibration force is determined when bending force and calibration coefficient are known. Significant factors for determination of bending force are: material of the circular plate, bending radius circular plate, diameter of the circular plate, thickness of the circular plate and method of loading of the circular plate. The calibration coefficient is determined by experiment. The analysis of bending plate is limited to the facts and figures used so far in the fabrication of spherical tanks, i.e. for deformations up to 1 %.
Journal of Material Sciences & Engineering | 2012
Zdenka Keran; Miljenko Math; Petar Piljek
The study concerns the analysis of significant contact friction changes by changing the size of crystal grains in the processes of free axisymmetric work pieces upsetting, initial height of 2 mm. The friction changes result with significant changes in forming force. This phenomenon usually characterizes micro forming processes. Using hard experimental data in the creation of numerical FE (finite element) model, a dependence of the changes of contact friction in correlation to the change of the work piece crystal grain size for three different grain sizes: 39, 47 and 76 μm is presented. It is shown that the friction factor is increased by reducing the size of crystal grains. Physical interpretation of the results is given by theory of Bowden and Tabor.
NUMIFORM 2010: Proceedings of the 10th International Conference on Numerical Methods in Industrial Forming Processes Dedicated to Professor O. C. Zienkiewicz (1921–2009) | 2010
Zdenka Keran; Miljenko Math; Marko Škunca
Although elastic springback makes a great challenge in sheet metal forming, it is also a value that is considered in the area of coining. It is a parameter that can often make many difficulties when coin should obtain the etching of the die. That can happen because of small coin height in which leading part takes material composition, its grain size and microstructure. It classifies coining process to a group of microforming processes. Therefore, an experiment has been carried out whose task was to provide data about percentage of elastic springback in total deformation during coining process of Al 99.5%. This has been carried out for three different grain sizes of the same material. An experiment has also included microscopic observation of gravure filling for mentioned grain sizes and also for different tool forces. The final result is a correlation between grain size and elastic springback in coining process, and also a correlation between grain size and gravure filling for different tool forces.
MATERIALS PROCESSING AND DESIGN; Modeling, Simulation and Applications; NUMIFORM '07; Proceedings of the 9th International Conference on Numerical Methods in Industrial Forming Processes | 2007
Marko Škunca; Zdenka Keran; Miljenko Math
Numerical simulation of bulk metal forming plays an important role in predicting a key parameters in cold forging. Comparison of numerical and experimental data is of great importance, but there is always a need of more universal analytical tools. Therefore, many papers besides experiment and simulation of a particular bulk metal forming technology, include an analytic model. In this paper an analytical model for evaluation of commercially available simulation program packages is proposed. Based on elementary theory of plasticity, being only geometry dependent, model represents a good analytical reference to estimate given modeling preferences like; element types, solver, remeshing influence and many others. Obtained, geometry dependent, stress fields compared with numerical data give a clear picture of numerical possibilities and limitations of particular modeling program package.
Key Engineering Materials | 2007
Branimir Barišić; Miljenko Math; Branko Grizelj
In order to determine the forming force in deep drawing and backward extrusion processes (on Al 99.5F7 specimens) the analytical, numerical and stochastic modeling and analysis of forming force on the basis of the Box-Wilson’s multi factorial experimental designs by use of rotatable experimental design were carried out. The goal of the paper is to predict the force in these different forming processes giving identical parts by means of different modeling approaches. This study will seek to compare the results of these modeling solutions with experimental results serving to check the correction and the verification of analytic, stochastic and numerically obtained results. Also, the scope of the present paper is to evaluate different parameters affecting these processes and to examine some experimental procedures in laboratory scale for the listed material in order to give more useful information in numerical and stochastic computations and also, to define the correlation among the parameters of these processes in order to improve the existing one and to raise it to a higher techno economic level. The increasing tendency for industrial parts cost reduction, quality improvement, materials savings, and the shortening of design and manufacturing time is more focused on this way of analysis of processes. These investigations are a basis for general conclusions about the forming force and they have a direct application in the projecting of these processes, tools and forming systems.
Interdisciplinary Description of Complex Systems | 2014
Petar Piljek; Zdenka Keran; Miljenko Math
Journal of Materials Processing Technology | 2004
Branimir Barišić; Goran Cukor; Miljenko Math
Journal of Materials Processing Technology | 2006
Marko Škunca; P. Skakun; Zdenka Keran; Leposava Sidjanin; Miljenko Math
Journal of Materials Processing Technology | 2008
Branimir Barišić; Tomaz Pepelnjak; Miljenko Math