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Numerical support for analysis of the fatigue behavior of cement based composites
Viszlay, Viliam ; Keršner, Zbyněk (referee) ; Seitl, Stanislav (advisor)
This thesis is focused on numerical analysis of fracture mechanics parameters in modified compact tension (CT) test. This CT test appears to be a suitable alternative to classic compact tension test for using for testing of quasi-brittle materials. The classic compact tension test is commonly used for fatigue testing of metallic materials and the geometry of used specimens does not allow using this test for quasi-brittle materials like cement based composites. The modified version of this test with cylindrical shape of the specimen allows us to test fatigue behaviour of quasi-brittle materials. In this thesis the influence of the modification of classic CT test on fracture mechanic parameters are determinated. In the next step, the influence of the position of steel bars (the position of loading force) on fracture mechanic parameters are evaluated. Obtained values are presented in graphs and calibration polynomials for each geometry are proposed.
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Numerical support for analysis of the fatigue behavior of cement based composites
Viszlay, Viliam ; Keršner, Zbyněk (referee) ; Seitl, Stanislav (advisor)
This thesis is focused on numerical analysis of fracture mechanics parameters in modified compact tension (CT) test. This CT test appears to be a suitable alternative to classic compact tension test for using for testing of quasi-brittle materials. The classic compact tension test is commonly used for fatigue testing of metallic materials and the geometry of used specimens does not allow using this test for quasi-brittle materials like cement based composites. The modified version of this test with cylindrical shape of the specimen allows us to test fatigue behaviour of quasi-brittle materials. In this thesis the influence of the modification of classic CT test on fracture mechanic parameters are determinated. In the next step, the influence of the position of steel bars (the position of loading force) on fracture mechanic parameters are evaluated. Obtained values are presented in graphs and calibration polynomials for each geometry are proposed.
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Utilization of two-parameter fracture mechanics in gears with thin rim
The aim of this work was to use FEM to estimate trajectory of the fatigue crack in gears with thin rim. The principles of the classical linear-elastic fracture mechanics and the two-parameter fracture mechanics were used to describe the process of gear failure. The minimum thickness of the gear rim (in which the failure mechanism is a fracture below the gear tooth) was numerically calculated. Numerical results were validated by comparison with experimental results obtained from available literature. It was found that involving of constraint give precise calculation of the consequent direction of the fracture angle and in some cases the constraint can cause significant change in prediction of fracture trajectory find out by classical linear-elastic fracture mechanics characterization.
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Influence of geometry on fatigue crack growth
Hutař, Pavel ; Náhlík, Luboš ; Knésl, Zdeněk
The paper describes an application of constraint based fracture mechanics to the behaviour of fatigue cracks. This work is focused mainly on the area of high cycle fatigue (corresponding to small scale yielding conditions) and different constraint levels are quantified by T-stress value. It is suggested that the fatigue crack propagation rate is controlled by an effective value of the stress intensity factor depending on the nominal value of the stress intensity factor, the yield stress of the material and the T-stress value. It is shown that in some cases the effect of geometry has a significant influence on the fatigue crack propagation rate and on the threshold values. The T-stress effect on plasticity induced crack closure is discussed. The approach suggested is intended to contribute a more reliable transfer of laboratory data to engineering structures with different constraint levels.
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