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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

2010

Vol. 10, No. 2

61-68

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.

Multi scale modeling and interpretation of tensile test of magnesium alloys in microchamber for the SEM

Kustra P., Milenin A., Shaper M., Gridin A.

Computer Methods in Materials Science

2009

Vol. 9, No. 2

207-214

In the presented paper magnesium alloy wire drawing process for medicine application is investigated. The magnesium alloy has a low plasticity at room temperature and cold drawing process is difficult. That why predicting of wire fracture is very important from theoretical and technological point of view. Analyzing of tensile test of magnesium alloys in micro and macro scale using results from 10000N Tensile/Compression Stage for the SEM, allow to understand a numerical model of fracture phenomena. The propose of this aim is to developed a mathematical model of flow stress for magnesium alloy and work out a parameters of fracture criterion using inverse method.

W niniejszym artykule rozpatrzono proces ciągnienia stopów magnezu dla zastosowań w chirurgii. Stopy magnezu mają niską plastyczność w temperaturze pokojowej dlatego proces ciągnienia na zimno jest trudny, a nawet praktycznie niemożliwy. Dlatego przewidywanie procesu pękania jest istotne z technologicznego i praktycznego punktu widzenia. Analiza próby rozciągania w mikrokomorze "10000N Tensile/Compression Stage for the SEM" w skali makro oraz skali mikro, pozwoliła na zrozumienie procesu pękania tych stopów. Celem niniejszej pracy jest opracowanie krzywych płynięcia oraz modelu matematycznego procesu pękania rozpatrywanych stopów magnezu oraz implementacja tych modeli do kodu metody elementów skończonych.