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Kalibrace potenciálové metody pro měření růstu únavové trhliny
Kotecký, Ondřej ; Degallaix, S. ; Polák, Jaroslav
The DC potential drop method widely used to follow long crack growth, was adapted to measure the growth and to estimate the shape of mechanically short fatigue cracks initiated on a small defect in an austenitic-ferritic stainless steel. The paper deals with problems of calibration of the method by the means of finite element analysis. A comparison between measured and actual crack length and crack front in notched specimens is presented.
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The proceedings of the 2nd konference of PhD students Multiscale design of advanced materials
Papers contributing to the solution of multilevel investigation and design of materials prepared either by members of doctorate team and PhD student investigating separately on the same institutions engaged in solution of doctorate project of Czech Science Foundation are contained in the proceedings. The contributions are oriented on theoretical and experimental aspects of materials designs arising form different approached from first principles up the continuum mechanics.
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Mechanical properties evaluation by means of instrumented indentation test
Brumek, J. ; Strnadel, B. ; Dlouhý, Ivo
An instrumented indentation study focusing on the materials with non-linear stress-strain behavior is presented. Indentation tests were applied on steel R7T. The observed data were analyzed and mechanical properties, such as yield stress, strain hardening exponent and elastic modulus were assessed. Experimental results of load-indentation depth test were compared with FEM solution. FEM analysis was applied on two-dimensional model described by elastic-plastic elements. Presented approach to prediction of mechanical characteristics is useful for estimation of remanent lifre of steels and other materials by using indentation method.
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The role of microstructure in racture behaviour of TiAl based intermetalics
Krahula, Karel ; Prokešová, Zdenka ; Dlouhý, Ivo
The contribution is focused on the analysis of the role of microstructural parameters in fracture behaviour of TiAl intermetalics at room and increased temperatures. Flexural strength and fracture toughness have been evaluated for alloys Ti-40Al-2Cr-2Nb-1B and Ti-46Al-0,7Cr-0,1Si-7Nb-0,2Ni. Positive effect of Nb on fracture resistance has been found; fracture toughness of the high Nb alloy increased at contemporary increase of flexural strength. Fracture surfaces have been evaluated using scanning electron microscopy showing the key role of mechanical twinning in deformation of both alloys followed. As a governing mechanism of crack nucleation microcrack formation at boundaries between mechanical twins and gama grains has been confirmed.
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Studium struktury a magnetismu FeCo při vysokých deformacích z prvních principů
Čák, Miroslav ; Legut, Dominik ; Šob, Mojmír
Total energies and magnetic moments of FeCo along the tetragonal deformation path are calculated using first-principles electronic structure methods. Total energies are displayed in a contour plot as a function of tetragonal distortion and volume; borderline between the ferromagnetic and nonmagnetic states is shown. The calculated energies may be used to predict the lattice parameters of FeCo thin films on various (001) substrates; here we study the FeCo film on the MgO(001) substrate. The calculated results are compared with available experimental data. The loss of magnetism of FeCo at low atomic volumes and large shape deformations is observed.
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Možné transformační dráhy spojující struktury C11b, C40 and C54 v MoSi2
Káňa, Tomáš ; Legut, Dominik ; Šob, Mojmír
We suggest three transformation paths between the ideal C11b , C40 and C54 structures of transition-metal disilicides. These three structures can be regarded as different stackings of identical planes of atoms. Each suggested transformation path consists in shifting these atomic planes in three directions. The shift of planes is described by one parameter p <0;1>. Along each path, we calculate the total energy of MoSi2 as a function of p. Our results confirm the structural order C11b → C40 →C54 in MoSi2. The C11b–C54 path exhibits the largest energy barrier, 2.5 eV/f.u (f.u. means the formula unit). The energy barrier of the C11b–C40 path is lower, 1.7 eV/f.u. and finally the energy barrier of the C40–C54 path is the lowest one, 1.4 eV/f.u.
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