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Numerical investigation of residual lifetime of the wheel during EN 13262 test
Matušek, P. ; Hutař, Pavel ; Náhlík, Luboš ; Knésl, Zdeněk ; Kunz, Ludvík
In this paper, the experimental set up corresponding to the test unit used for the full-scale fatigue test has been modelled. The numerical method for reliable estimation of residual fatigue lifetime of wheel web tested according to EN 13 262 Standard has been developed. Numerical calculations are based on finite element method utilizing the system ANSYS. The experimentally observed cracks in the wheel web have been taken as the initial crack configuration. Numerical calculations simulating the initial crack growth in the wheel web loaded by experimental set up have been performed. Under assumptions of linear elastic fracture mechanics the residual fatigue life of the cracked wheel has been predicted.
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Dimensioning of thick-walled pipe in creep
Zouhar, Michal ; Hutař, Pavel ; Náhlík, Luboš ; Hlavoň, P.
The numerical simulations of the creep in the case of X10CrMoVNb91 steel were performed. Geometry of the objects studied well-fit usual parts of the pipe system. The discrepancies between numerical simulations and usual standard Design By Formula (DBF) used for the pipe system lifetime prediction were found. Therefore, accurate numerical simulations based on creep description of the material behaviour is necessary for the accurate estimation of the service conditions.
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Simulation of the crack growth in the weld of the polyolefin pipes
Ševčík, Martin ; Hutař, Pavel ; Náhlík, Luboš
The aim of this work was to study the effect of the material properties change due to the butt welding on the stress intensity factor in polyolefin pipe. The gradient change of the Young’s modulus was assumed. The crack was located in the middle of the affected zone. The stress intensity factors estimated in both graded region and basic material (homogenous case) were compared. Strong influence of the graded region on the value of the stress intensity factor was observed. Therefore, for realistic estimation of the welded pipe lifetime the change of the material properties inside the polymer weld should be taken into account.
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Determination of mechanical properties of thin films by nanocompresion
Kuběna, Ivo ; Hutař, Pavel ; Náhlík, Luboš ; Kruml, Tomáš
Measurements of mechanical properties of objects with micrometric (or even smaller) dimensions is still not a common task. In this paper, the possibility of evaluation basic mechanical properties of a thin film by nanocompression is demonstrated. Cylindrical specimens with the axis normal to the film plane, attached by the bottom to the substrate, are prepared by the focused ion beam technique. Such pillars are deformed by a nanoindenter outfitted by a flat diamond punch. An equivalent of compression curve is obtained. It is possible to measure directly parameters as the yield stress, stress at a chosen strain level or work hardening rate. Finite elements modelling is necessary for the Young modulus evaluation. It is shown that the Young modulus can be evaluated quite precisely, even if the geometry of the pillar is not perfect.
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Fatigue properties of Eurofer steel developed for fusion application
Kuběna, Ivo ; Kruml, Tomáš ; Hutař, Pavel ; Náhlík, Luboš ; Seitl, Stanislav ; Polák, Jaroslav
In this study fatigue properties of Eurofer 97 steel in room temperatures were measured. Fatigue parameters of the cyclic stress - strain curve and fatigue life curves (Coffin-Manson curve and derived Wöhler curve) were evaluated. Major attention was given to the measurement of kinetics of fatigue crack growth by two different methods. The initiation sites of fatigue cracks and short crack growth were observed and measured on cylindrical specimens with shallow notch. These cracks had a length from 20 micrometers to 1 mm. Kinetics of growth of long cracks with the length 15-30 mm was measured on CT specimens. It was found that results obtained by the both methods are in a good agreement if the J-integral is used. It was possible to determine the threshold values of J-integral and stress intensity factor and to calculate the Paris law parameters.
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Vliv rohové singularity na tvar únavové trhliny
Hutař, Pavel ; Náhlík, Luboš ; Knésl, Zdeněk ; Seitl, Stanislav
Due to the existence of vertex singularity at the point where the crack intersects the free surface, stress distribution around the crack tip and the type of the singularity is changed. In the interior of the specimen the classical singular behaviour of the crack is dominant and can be described using generally known analytic equations. Contrary to this, at the free surface or in the boundary layer close to the free surface the vertex singularity is significant. The influence of vertex singularity on crack behaviour and crack shape for a three-dimensional structure is described in this paper. To estimate the influence of the free surface on fatigue crack growth rate the model of a general singular stress concentrator was applied. The estimated fatigue crack shape can help to provide a more reliable estimation of the fatigue life of the structures considered.
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Některé aspekty chování polymerních částicových kompozitů
Hutař, Pavel ; Knésl, Zdeněk ; Majer, Zdeněk ; Prod’homme, G. ; Náhlík, Luboš ; Nezbedová, E. ; Veselý, P.
Computation of the internal stress and strain fields in the microstructural level of the studied composite and understanding of microcracks behaviour in the interaction with particles is the first step to understanding the global behaviour of the composite based on microstructural morphology. Therefore, particle reinforced composite has been modelled as a three-phase material with homogenously distributed coated particles and numerically studied on the microscopic scale using finite element modelling. The FEM modelling and unit cell models provide an effective tools for parametric study of the three-phase composite mechanical properties.
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Odhad zdánlivé lomové houževnatosti keramických laminátů založený na zobecněném faktoru hustoty deformační energie
Náhlík, Luboš ; Šestáková, Lucie ; Hutař, Pavel
The paper presented deals with fracture behavior of ceramic laminates. Assumptions of the linear elastic fracture mechanics and small scale yielding are considered. In this frame the residual stresses in individual layers of Al2O3/5vol.%t-ZrO2 (ATZ) and Al2O3/30vol.%m-ZrO2 (AMZ) are determined. The procedure based on generalization of Sih's strain energy density factor to the case of a crack touching the interfaces between two dissimilar materials is used for determination of effective values of stress intensity factor at material interfaces.Important increase of the fracture toughness at AMZ/ATZ interface was predicted in comparison to the fracture toughness of individual material components. Predicted values were compared with data available in literature and mutual good agreement was found. Procedure suggested can be used for estimation of resistance to crack propagation of multilayered structures and its design.
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Efekt velikosti částic na lomové chování polypropylenového kompozitu
Nezbedová, E. ; Knésl, Zdeněk ; Hutař, Pavel ; Majer, Zdeněk ; Veselý, P.
The addition of mineral fillers to polypropylene (PP) can profoundly change the mechanical properties of polymer system. The properties of the particles themselves (size, shape, and material properties) can have significant effect on the global behaviour of composite, particularly on its toughness and stiffness. This contribution is focused on effects of particles size and their density on fracture toughness of polyprophylen particulate composite. The effect was studied from the experimental as well as from the theoretical point of view. The change of fracture toughness was estimated with utilisation of linear elastic fracture mechanics approach. The composite was modelled as a three-phase material with homogeneously distributed coated particles and numerically simulated using the finite element program ANSYS.
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