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Thinning of kaolin slurry
Vlasák, Pavel ; Chára, Zdeněk ; Konfršt, Jiří
After mixing kaolin with water attractive and repulsive forces between kaolin particles initiate process of coagulation and peptisation, respectively. The coagulation process in the kaolin slurry gives rise to voluminous aggregates of kaolin particles, where a great deal of water is fixed.
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Hydraulics of overflowed bridge
Chára, Zdeněk ; Vlasák, Pavel
The paper deals with an open channel flow around model of a bridge when the water depth is higher than height of the bridge opening. Both the pressured flow through bridge opening and free surgace flow over the model were studied. For both cases discharge coefficients were determined and for overflowed model also the velocity profiles were measured to evaluate the ratio of discharges going below and over the bridge model.
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LDA measurement of axial velocity profile in tall vessels with a draught tube
Brož, J. ; Severa, Miroslav ; Jirout, T. ; Rieger, F.
Large tall vessels with a draught tube are used for the mixing of suspensions especially in cases where high homogeneity and heat tranfer are desirable. The article describes flow behaviour of liquid in the vessel with a draught tube. LDA method (Laser Doppler Anemometry) was used for measurement axial velocity profile. The experimental configuration for LDA method was produced by firm DANTEC. Experimental results are compared with numerical simulation and other experiment.
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Short-time turbulent disturbances in pulsatile flow
Kořenář, Josef
In the pulsatile flow in tubes near the laminar/turbulent transition zone, the short-time turbulent disturbances arise and fade away in every period. Moment of arise, endurance, course of intensity and moment of disappearing of those disturbances within a period are dependent on flow parameters like mean Reynolds number, Womersley number and flow rate ratio.
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Fracture process zone of concrete: analysis of aggregate-crack interaction
Keršner, Z. ; Náhlík, Luboš ; Knésl, Zdeněk
Concrete is modelled as a two-phase material. Behaviour of a crack with its tip on the interface between two different materials - hardened cement paste (matrix) and aggregate (particle) - is studied. In contrast to cracks in homogeneous materials the stress singularity for a crack terminating at the interface is of the type r -lambda, where the value of the stress singularity exponent, lambda, is in the interval 0 < lambda < 1. Than classical fracture mechanics theory and criterion cannot be applied. In the paper a new stability criterion is used to estimate the critical stress for the intersection of coarse aggregate particles.
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Formulation of the brittle failure conditions for composite bodies
Náhlík, Luboš ; Knésl, Zdeněk
A stability criterion based on generalized strain energy density factor for a crack terminating at the bi-material interface is suggested. The strain energy density distribution in the vicinity of the crack as well as the generalized stress intensity factors, and the crack propagation direction are calculated. The crack is oriented arbitrarily to the interface and both stress singularities around the crack tip are taken into account. The problem is solved by combination of analytical and numerical approaches. A numerical example of application of the proposed approach is presented.
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Application of contour integrals to assessment of notch stability in linear elasticity
Gröger, Roman ; Knésl, Zdeněk
The article yields a teoretical background of a well- sophisticated numerical method for calculation of GSIF and T stress, especially for case when the integration across the nonhomogeneous material interface is unavoidable. The main advantage of the integral approach over the well-known direct methods is its accuracy induced by monotonous convergence of the solution. This work contributes to more accurate description of the instability state of V-notches in composite structures.
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THE INFLUENCE OF T-STRESS FOR RELATIONSHIP BETWEEN CTOD AND J
Hutař, Pavel ; Knésl, Zdeněk
Relations between crack opening displacement (CTOD) and other fracture mechanics parameters are of a great importance in fracture mechanics. The basic aim of this paper is to describe an influence of T-stress on the plastic eta factors, plastic rotation factor and proporcional factor, i.e. the factors correlating J-integral and CTOD. Specimens with different values of T-stress (compact tension,three point bend and single edge cracked tension) are analysed by finite element method, the factors are calculated as functions of corresponding crack length and results obtained are discussed from the point of view of two-parameter fracture mechanics.
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Analysis of crack propagation in vicinity of bi-material interface in framework two parameter fracture mechanics
Seitl, Stanislav ; Knésl, Zdeněk
Existence of the interface between regions with different elastic properties have a pronounced influence on the behaviour of cracks The aim of the present contribution is an analysis of a crack growing in a vicinity of the interface between two different elastic materials.. The basic assumption of the contribution corresponds to two-parameter linear elastic fracture mechanics. The values of stress intensity factor KI and KII corresponding to normal and shear mode of loading and the value of T-stress are calculated for a generally oriented crack approaching to the interface. The calculations are performed by finite element method for short and long cracks. The dependence of KI, KII and T values on the distance and the orientation of a crack with respect to the interface is studied. It is shown that short cracks are influenced by the presence of the interface more significantly in comparison with long cracks. The results contribute to better understanding of short cracks behaviour in relation to microstructure of material.
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