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DISPLACEMENT FIELD ANALYSIS IN WEDGE SPLITTING TEST\nSPECIMEN BY ODM METHOD
Seitl, S. ; Miarka, P. ; Růžička, V. ; Malíková, Lucie ; Merta, I.
Multi-parameter fracture mechanics is nowadays quite extensively applied when cracked\nstructures/specimens are investigated. The reason is that it has been shown that it can be\nhelpful and bring more accurate results when fracture processes happen in a larger\nregion around the crack tip, what can be typical for material like concrete or other\nmaterials with quasi-brittle behaviour. Various relative crack length configurations have\nbeen chosen in order to investigate the importance of the higher-order terms of the\nWilliams power expansion on the crack-tip stress field distribution in Wedge splitting\ntest specimen. The higher-order terms are calculated by means of the over-deterministic\nmethod from displacements of nodes around the crack tip obtained by a finite element\nanalysis in different radial distances from the crack tip. The effect of the constraint level\nis investigated. Although the third and higher terms of the Williams series are very often\nneglected, their influence on the opening stress values is investigated.
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Effect of the load eccentricity on fracture behaviour of cementitious materials subjected to the modified compact tension test
Seitl, Stanislav ; Ríos, J. D. ; Cifuentes, H. ; Veselý, V.
Fracture properties of quasi-brittle cementitious composites are typically determined from the load–displacement response recorded during a fracture test by using the work-of-fracture method or possibly other relevant fracture models. Our contribution is focused on a set of experimental tests which are used to study the fracture behaviour on notched dog-bone-shaped specimens made of cementitious materials. These specimens are subjected to modified compact tension (ModCT) test under a specific range of eccentricity of the tensile load. This type of test generates a stress state in the specimen ligament which combines a direct tension with a defined level of bending due to eccentricity of the tensile load. Several values of relative notch length are also considered. While the crack propagates, a variety of stress states, resulting in variations in the crack-tip stress and deformation constraint, appears in the ligament zone because of the changes in the eccentricity of the applied load, which influences the fracture behaviour of the investigated specimens. The K-calibration, T-stress, CMOD and COD curves for ModCT specimens are introduced and variations of these curves with varying load eccentricity are discussed.
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Visual Perception and Phonological Forms of Lexemes in the Czech Sign Language (A Frequency Analysis of Selected Parameters of Signs)
Klabanová, Lucie ; Richterová, Klára (advisor) ; Nováková, Radka (referee)
This bachelor work deals with problems of constraints in sign languages, especially the constraints of visual perception. Part of the work is an overview of general knowledge about constraints in sign languages. There are also presented results of frequency analysis of selected sign parameters in some foreign sign languages. Included is also knowledge gained from studies aimed at identifying locations of visual interest while watching sign language. Within own practical research, there are analyzed signs of three areas of Czech sign language: colours, calendar and time units and family, in terms of sign typology, handshape and location of articulation. There is also an experiment focused on detection visual locations of interest, while watching Czech sign language with occurrence of Czech finger alphabet. Keywords: Czech Sign Language, visual perception, constraints, location of articulation, handshape, type of sign
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Numerical Analysis of the Thickness Influence on the Stress Field at Crack Tip for Different Poisson´s Ratios
Seitl, Stanislav ; Hanzlovský, Radovan ; Fernandez, C.
The influence of in- and out- of plane constraints on the behaviour of cracks under mode- I loading condition is studied. The independence of the stress intensity tensor structure, with respect to the specimen thickness B shows that under loss of constraint conditions higher order tensor members of the Williams expansion must be considered to characterize the singular stress field, and to explain the increasing apparent fracture toughness resulting experimentally for decreasing specimen thickness. A numerical study of the effect of Poisson’s ratio on stationary mode I crack tip fields is presented in the contribution. Finite element calculations for two-dimensional (v =0) and three-dimensional bodies are performed and compared. Further, the stress intensity tensor K, and the elastic txx and tzz components of the tij constraint tensor in the middle of a three-dimensional crack front are determined using direct methods for the same level of loading.
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Influence of T-stress on residual fatigue life of railway wheel set
Náhlík, Luboš ; Hutař, Pavel ; Knésl, Zdeněk ; Matušek, P.
Influence of T-stress on residual fatigue life of railway wheel set is analysed. The influence of constraint caused by different specimen geometry on fatigue crack growth is analyzed and a phenomenological model is proposed to correlate the fatigue crack propagation rate under different constraint levels. The approach is based on an application of two-parameter fracture mechanics and the corresponding calculations are performed according to the finite element method. The constraint level is quantified by the value of T-stress. The result presented makes it possible to relate experimentally measured data obtained from specimens with different geometries and thus contribute to more reliable estimates of the residual fatigue life of structures.
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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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Plasticity induced crack closure for specimens with different geometries
Hutař, Pavel
The article is solving problem of plasticity induced crack closure for specimens with different geometries. The specimens with low level of constraint (MT-specimen) produced higher level of opening stress intensity factor than specimen with high level of constraint (CT-specimen). It was concluded that for better estimation of residual fatigue life of structures is necessary to consider effects of crack closure.
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