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Simulations of the haemodynamics in the elatic model of vascular graft
Konfršt, Jiří
The paper presents simulation of blood flow in elastic model of crimpted vascular graft (produced by VÚP-Brno CZ; type Ra; internal diameter 9 mm). The LDA method has been used for the investigations of pulsatile flow inside the model. Measurements are realised using three Re numbers with Newtonian and non-Newtonian fluid, wich simulate rheological characteristics of blood.
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Two-parameter characterisation of a crack growing in the vicinity of the material interface
Gröger, Roman ; Knésl, Zdeněk
A crack propagating in the vicinity of the material interface is analyzed. The problem is solved in the range of two-parameter linear elastic fracture mechanics. The aim of the contribution is to assess the influence of T stress on the direction of a crack growing to the interface. The interface is modelled for different material properties characterised by the Dundur's composite parameters. First the effect of the interface on T stress value is studied and values of KI, KII and T stress are estimated. Consequently the two-parameter modification of MTS criterion and Sih's SED criterion is used for prediction of a crack propagation direction. Both these approaches are compared. It is concluded that the negative values of T stress stabilize the crack propagation perpendicularly to the interface.
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Influence of grain orientation on threshold values of short fatigue cracks
Náhlík, Luboš ; Knésl, Zdeněk
The influence of a grain boundary on the propagation of a fatigue crack is studied. To this aim the grain boundary is considered as an interface between two different materials with their elastic constants depending on the orientation of the adjacent grains. The main goal is to estimate the threshold value of a microstructurally short fatigue crack propagating through the grain boundary. The corresponding threshold values are calculated as a function of material parameters of grains. Corresponding modelling have been performed by combination of analytical and numerical approach. For numerical calculations the finite element system ANSYS has been used. The model describes only one of many aspects of short fatigue crack behaviour and the results obtained contribute to a better understanding of microstuctural aspects of short fatigue crack growth.
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Quantitative Assessment of the T-stress in Short Fatigue Crack Propagation
Seitl, Stanislav ; Knésl, Zdeněk
Two parameter constrained based fracture mechanics is applied to quantitative assessment of microstructurally short fatigue cracks propagation. The different levels of a stress constraint are quantified by T-stress. Corresponding calculations are performed by finite element method (ANSYS system). The values of the T-stress are numerically estimated as a function of material properties, location and orientation of the short crack with respect to the grain boundary. The influence of constraint on small fatigue crack growth kinetic is discussed. It is shown that the level of constraint of the near-tip fields for microstructurally short fatigue cracks may influence the fatigue crack rate substantially.
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