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1

Sinking of Ultra-Thick-Walled Double-Layered Aluminium Tubes

Gülseren B., Bychkov O., Frolov I., Schaper M., Grydin O.

Archives of Metallurgy and Materials

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2018

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Vol. 63, iss. 1

365--370

EN

This work deals with the tube sinking process. The main purpose is to develop a process chain for the manufacturing of ultra-thick-walled tubes with the lowest possible diameter. The base material is a hot extruded tube consisting the aluminium alloy AA6063 with the dimensions 9,9 ×1 mm. The drawing tools include several dies with various exit holes, a drawing bench and a muffle oven to produce ultra-thick-walled tubes with dimensions 5,02…5,03 × 1,54…1,59 mm. The process has been applied successfully. With a double-layered tube, it was possible to reach a low diameter/wall-thickness ratio of 3,3 at tube sinking process. Subsequent pull-out tests showed that by reaching the threshold outer tube diameter value of Ø 5 mm the joining strength increased from 1,3 MPa to 6,2 MPa. It could be observed that the heat treatment reduced the joining strength for the double-layered tubes with diameter of 5 mm, whereupon for the bigger tubes diameter it has no significant influence on the joining strength.

2

Opracowanie za pomocą metody elementów brzegowych, kalibracja i weryfikacja modelu utraty spójności specjalnych stopów magnezu w skali mikro

Milenin A., Byrska-Wójcik D. J., Grydin O., Schaper M.

Rudy i Metale Nieżelazne

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2011

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R. 56, nr 11

581-587

PL

Specjalne stopy magnezu (MgCa0.8, Ax30) o podwyższonej biozgodności mogą być zastosowane do produkcji resorbowalnych nici chirurgicznych. Problem stanowi ich niska plastyczność w temperaturze pokojowej. Proponowany model numeryczny pozwoli dobrać parametry procesu ciągnienia i określić graniczne możliwości produkcji. Model numeryczny odkształcenia w skali mikro został wykonany za pomocą metody elementów brzegowych. Procedurę kalibracji modelu oparto na eksperymentalnych badaniach w skali mikro, przeprowadzonych w mikrokomorze do SEM. Jako funkcję celu zaproponowano kwadrat różnicy porowatości próbki obliczonej w modelu i otrzymanej eksperymentalnie. Do kalibracji wykorzystano wyniki testów na rozciąganie, natomiast do weryfikacji modelu przeprowadzono inny rodzaj badań in situ opartych o ścinanie próbki. Powstałe narzędzie numeryczne może być połączone z modelem procesu ciągnienia w skali makro, dzięki czemu możliwa będzie optymalizacja procesu, uwzględniająca mechanizmy, zachodzące w mikrostrukturze.

EN

Special magnesium alloys (MgCa0.8, Ax30) with high biocompatibility can be applied for production of soluble surgical threads. The problem is low plasticity of these alloys at room temperature. The proposed model allows to set the drawing process parameters and to determine the maximum of production possibility. The numerical model of deformation in mi croscale is developed by boundary element method. The procedure of model calibration is based on experiments in microtensile/compression stage for a SEM. As a goal function the square of difference between theoretical and experimental values of porosity was proposed. The results of "in situ" tensile tests were used for calibration purpose and shear test was prepared for verification of model. The developed numerical tool can be coupled with macroscale drawing process model, so the optimization of drawing process will be possible with considering microstructural mechanisms.

3

Modelowanie mechanizmu utraty spójności stopu MgCa0,8 w procesie odkształcenia na zimno

Milenin A., Byrska D. J., Kustra P., Heidenblut T., Grydin O., Schaper M.

Rudy i Metale Nieżelazne

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2010

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R. 55, nr 4

200-208

PL

Stopy magnezu o podwyższonej biozgodności posiadają niską plastyczność w temperaturze pokojowej. Opracowanie modelu utraty spójności jest niezbędne do projektowania technologicznych parametrów procesu ciągnienia tych stopów. W artykule zaproponowano model numeryczny procesu utraty spójności dla przykładowego stopu MgCa0,8 z uwzględnieniem mechanizmu mikropękania na poziomie mikrostruktury. Pierwsza część pracy jest poświęcona doświadczalnej analizie procesu rozciągania próbek w specjalnej mikrokomorze 10 000N Tensile/Compresion stage for SEM, która pozwala na obserwację odkształcanej mikrostruktury za pomocą mikroskopu skaningowego. Analiza wyników eksperymentu wykazała, że mikropękanie zarodkuje na granicach ziaren a następnie propaguje wzdłuż granicy, prowadząc do globalnego zerwania materiału. Uzyskano graniczne wartości odkształceń, niepowodujących powstawania mikropęknięć. Do interpretacji testów na poziomie makro wykorzystano symulacje procesu rozciągania za pomocą metody elementów skończonych. Do wyznaczenia mechanicznych charakterystyk badanego stopu na poziomie makro wykonano testy na rozciąganie w maszynie Zwick250. W dalszej części artykułu opisano model utraty spójności stopu MgCa0,8 w skali mikro. Zaproponowano podejście do symulacji zjawiska mikropękania po granicach ziaren, oparte na metodzie wprowadzenia cienkiej warstwy elementów modelujących granice. Dla materiału granicy zaproponowano model umocnienia oraz kryterium mikropękania. Weryfikacja modelu w skali mikro była oparta na porównaniu mikrostruktur z wynikami modelowania na różnych stadiach rozciągania próbki.

EN

The MgCa0,8 magnesium alloys can be applied to production of surgical threads. Low plasticity of this alloys cause difficulties with cold forming. Composition of alloys which are used in medicine is selected, so that surgical threads made from this alloys will have high bio-compatibility and adequate solubility in human body. The purpose of this work is development a mathematical model of MgCa0,8 fracture phenomena in micro scale. According to reached results, the analysis of fracture phenomena in macro scale is not sufficient and, therefore the model in micro scale is necessary. Model of wire drawing can be used to optimize the parameters of drawing process and to predict the ductility of material. The first part of the work is focused on experimental studies of tensile tests, which is used to work out micro scale fracture model. The experiment which was done at the University of Hannover show that fracture in MgCa0,8 alloy had started in grains boundaries and, in consequence had been propagated along grains boundaries. During the tensile test the photos of microstructure had been taken and then, this data were applied for modelling in micro scale. For simulation of test in macroscale, the FEM is used. For identification a yield stress curve for the macro scale model the experiments in Zwick250 were used. The second part of work was focused on development a multiscale numerical model of fracture phenomena. In micro scale model the finite element method was used. The Abaqus 6.7 was used in calculations. For modelling of boundaries of grains the Thin Layer Method was used. The properties of material in grain boundaries were determinate in the inverse analysis. The aim of this analysis was to obtain results of numerical calculations comparable with the experimental data. The boundary conditions and shape of model in micro scale were obtained from process simulation in macroscale. The fracture modelling of the material is made on the basis of the Johnson-Cook fracture initiation criterion and it is an integral component of the Abaqus software. The inverse analysis was used to obtain parameters of this criterion. The final results of numerical model of tensile test in micro-scale were performed and the prediction of fracture phenomena in grains boundaries is observed. The model described in this paper always predict ductility quite well, but sometimes the different with experiments are observed. It is mainly implicated by the fact that many simplifications were made in this approach. Using the FEM to modeling the microstructure makes impossible introduction the big number of grains, because it generates the big number of nodes. The originality of this paper is a new approach to fracture modelling in micro scale, based on physical and numerical methods of modelling.

4

The experimental research and the numerical modeling of the fracture phenomena in micro scale

Milenin A., Byrska D., Grydin O., Shaper M.

Computer Methods in Materials Science

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2010

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Vol. 10, No. 2

61-68

EN

Magnesium alloys with increased bio-compatibility are applied in medicine for the sake of high compatibility and solubility in human body. Production of surgical threads to integration of tissue can be example of the application of these types of alloys. The MgCa0.8 magnesium alloy has a low plasticity at cold deformation, therefore, the drawing process of thin wire is difficult. Prediction of wire fracture in a drawing process of MgCa0.8 alloy is very important from theoretical and practical point of view. The macro scale fracture models are not capable to predict the important phenomena, such as cracking in grains boundaries, moment of initiation of micro-cracks, stress relaxation in grain after micro-cracking etc. Present work is dedicated to the development of a numerical model of MgCa0.8 fracture phenomena prediction in micro scale. The first part of the work is focused on experimental studies: tensile tests, which are data source for the flow stress model of MgCa0.8 alloy and metallographic analysis of material for micro scale fracture model. To understand fracture mechanism, physical modeling in 10000 N tensile/compression stage for a SEM for MgCa0.8 magnesium alloy was performed. This analysis shows that the material is cracking at the grain boundaries. Experiments in the chamber of SEM allows understanding of the fracture mechanism in special magnesium alloy MgCa0.8 and determining the empiric coefficients of fracture model in micro scale. The limit of deformation before initiations of micro-cracks was obtained. The second part of the work is focused on the development of the micro scale numerical model of fracture. The boundary element method is proposed for micro scale model. The mathematical model of fracture is developed for the two dimensional domain. The elastic-plastic theory of plasticity is used.