Materials Science Forum Vol. 729

Abstract: The testing of creep resistance (for example σ_{1%/100000 h}) of metals has been required for a long time (about 10 years) and some methods have been worked out to decrease testing time. The application of these methods has some difficulties. Now we have worked out a new empirical method to reduce testing time, namely COD measuring at an elevated temperature. The paper presents this method, which makes it possible to determine creep properties by measuring the materials COD at an elevated temperature. To determine COD we use notched samples with different radii and we tear them at an elevated temperature. The determination of COD is based on the Czoboly Radon method. By opening three different radii notches we approximate to zero radius which gives the COD. Master Curves of COD and creep resistance connections were drawn at 500 °C, which is not dependent on materials and they can be used for determining Creep Properties from COD measured at 500 °C. This method can be used for the comparison of the creep resistance of materials and for that of the creep properties of different zones of welded joints. The method is found useful in technical practice.

Abstract: An experimental stirring unit (inductor) using travelling magnetic field was tested for developing a solidification facility equipped with a magnetic stirrer. The investigations were performed by using an Sn50Pb alloy at temperature of 230°C. In the course of the experiments, the magnetic pressure developing in the metallic melt, the flow velocity of melt and the loss of flow were investigated using the TMF inductor.

Abstract: The pressure-temperature-specific volume relation of polymers is important not only for physical chemistry, but they are very significant input data for injection molding simulation software. Todays methods for measuring pvT data are slow, measurements can take days to be carried out, and in many cases the accuracy of the measurement is unsatisfactory. In our work, a new measuring method has been developed which makes the determination of the pvT relation faster compared to conventional processes within injection molding processing conditions. For the measurements a special injection mould was developed, in which the pvT relation of the material can be determined from the shrinkage in the mold. The data measured by the new method using polypropylene at a mold temperature of 23°C were compared to the data given in the database of the simulation software.

Abstract: The ε martensite phase was investigated in three types of FeMn (Cr) steels by means of metallographic, EBSD and XRD methods as well as by dilatometric and DSC examinations during heating and cooling. In the course of the latter examinations, the transformation temperatures (Ms, A_s) of ε martensite were determined in the previously deformed samples as well. The results were also compared to the thermodynamic data published in the references describing the γε and γα transformations.

Abstract: A strange self-sustained oscillation in plastic uniaxial tension of various materials is called the Portevin Le Chatelier (PLC) effect. In modelling PLC dynamic strain aging is the common way of explanation. It is based mainly on dislocation dynamics. Experimental studies show the negative strain rate dependence (NRS) is always present at PLC. By using continuum mechanics and dynamical systems theory we find that NRS is the essential reason of it.

Abstract: The prediction of third type boundary conditions occurring during heat treatment processes is an essential requirement for characterization of heat transfer phenomena. In this work, the performance of four optimization techniques is studied. These models are the Conjugate Gradient Method, the Levenberg-Marquardt Method, the Simplex method and the NSGA II algorithm. The models are used to estimate the heat transfer coefficient during transient heat transfer. The performance of the optimization methods is demonstrated using numerical techniques.

Abstract: By applying the cellular automaton method the short-range diffusion processes in metals can be efficiently simulated. Several examples for the two-and three dimensional modeling of recrystallization and grain-coarsening are know at the literature. In some previous works, results have been performed concerning the two-dimensional, stochastic automatons of grain-coarsening, recrystallization and allotropic transformation. In order to use these simulations also in technological processes, it is necessary to scale the results reached by the simulation. The primary aspect of adapting the automaton in technological processes is the quick-operating simulation. The aim is to develop a most simplified, scalable cellular automaton by which scaling can be efficiently performed.

Abstract: In the manufacture of products requiring multi-step wire drawing, it is helpful to use software that can aid in planning and that can calculate the values needed for optimum performance. The model described by analytical closed/explicit formulas provides the shortest calculation time. The aim of this study is to create a model described by analytical closed/explicit formulas approximating the measured data in the best way. An objective mathematical procedure are defined for model selection, and the selected model is proposed for the development of software with a short calculation time that optimizes the technological parameters of multi-step wire drawing and plans the drawing technology.

Abstract: Weakest points of carbon nanotube junctions have been determined by molecular mechanical algorithms. This algorithm is based on the application of the so-called Brenner potential function, atomic forces are calculated from the derivatives of the potential function describing the energetics. Behavior of various types of symmetric Y-junctions is studied with respect to axial tensile load.

Abstract: Having reviewed the literature on cutting and based on the optical, electron-optical and morphological examinations of wear processes we have reached the conclusion that it is possible to describe the abrasive, adhesive and thermally activated diffusion, oxidation processes in a single mathematical model. The model is a non-linear autonomous differential equation, which can be solved by simple numerical methods. The complex wear equation was validated by the results of the cutting tests performed with P20 carbide on C45 carbon steel. If we have this data, we can calculate the activation energy of the process determining the nature of the wear process. The apparent activation energy of wear is Q=151,7kJ/mol. The model can even be used with changing technological parameters, and the data necessary for the constants of the wear equation may as well be determined even by measurements performed on the tool during industrial manufacturing. By the mean of this data, we can calculate the activation energy determining the nature of the wear process.