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Rheology and texture of multiphase emulsion systems
Štern, Petr ; Pokorný, J.
Sensory and texture analyses are important tools to characterise the acceptance of food products by consumers. The aim was to correlate the results of rheological and sensory analysis because they can directly an more easily be applied in production and quality control. As an example were chossen Tartar souces - emulsion of edible oil in an aqueous phase consisting of water, salts, vinegar, modified starch and other flavoring. Functional relations between rheological parameters of tartar souces and sensory characteristics were determined.
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Crack propagation through a material interface
Náhlík, Luboš
This paper describes a study of the fatigue crack propagation through a material interface of two different elastic materials under assumptions of linear elastic fracture mechanics. Two procedures for estimation of threshold value for further crack propagation from bi-material interface to the second material are suggested. Special attention is devoted to crack perpendicularly oriented to the bi-material interface. The first one is based on modified Sih?s strain energy density concept and the second one on the size of area of the plastic zone in front of the crack tip. It is shown that the corresponding fatigue threshold value is strongly influenced by the existence of an interface between two materials. As a numerical example the procedures are in applied on body with protective layer. The calculation of the corresponding threshold values and comparison of both suggested procedures is performed. Both procedures make it possible to decide whether the crack will stop at the interface or will continue growing into the second material. The results generally contribute to a better understanding of the failure of structures with protective layers.
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Concrete as a two-phase material: statistical/sensitivity modelling of failure
Keršner, Z. ; Náhlík, Luboš ; Knésl, Zdeněk
Concrete is represented as a two-phase material. Behaviour of a crack with its tip on the interface between two different materials ů hardened cement paste (matrix) and aggregate(particle) ů is modelled. Input variables of the model are considered as random variables using LHS method/FREET software. Then results of statistical/sensitivity analyses of output variable ů the critical stress for the intersection of coarse aggregate particle ů are presented.
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Fracture behaviour of the short crack near the stress concentrator
Hutař, Pavel ; Knésl, Zdeněk
A two-parameter fracture mechanics method is applied to small cracks near a stress concentrator. The small crack in the present contribution is considered as crack influenced by the stress concentrator. The sharp V-noch or V-noch with radius $R$ are studieded here. The effect of V-notch geometry on the small crack fracture parameters is analysed. The necessary calculations are performed by using a finite element method (system Ansys). Obtained results are discussed from point of view of the small crack behavior. The small fatigue crack growth is especially influenced by the constraint level. The results improve the quality of fatigue life estimation of structure with concentrators.
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Crack propagation through a material interface
Náhlík, Luboš
This paper describes a study of the fatigue crack propagation through a material interface of two different elastic materials under assumptions of linear elastic fracture mechanics. Two procedures for estimation of threshold value for further crack propagation from bi-material interface to the second material are suggested. Special attention is devoted to crack perpendicularly oriented to the bi-material interface. The first one is based on modified Sih?s strain energy density concept and the second one on the size of area of the plastic zone in front of the crack tip. It is shown that the corresponding fatigue threshold value is strongly influenced by the existence of an interface between two materials. As a numerical example the procedures are in applied on body with protective layer. The calculation of the corresponding threshold values and comparison of both suggested procedures is performed. Both procedures make it possible to decide whether the crack will stop at the interface or will continue growing into the second material. The results generally contribute to a better understanding of the failure of structures with protective layers.
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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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Determination of T stress for arbitrary oriented crack terminating at interface between two dissimilar materials
Gröger, Roman
The most important factors describing the fracture-mechanics behavior of layered structures are the generalized stress intensity factor and also T stress describing the amplitude of the stress field independent on the radial distance from the crack tip.. Direct methods of the calculation of such parameters are well known and their accuracy is critically assessed by the experimental measurements. The present work proposes an alternative method of determining of the elastic T stress based on the validity of the reciprocal work theorem using the integration of the strain energy along a circular path surrounding the crack tip. The results obtained from a model of a crack terminating at interface between two dissimilar elastic materials are compared with the usually used direct approach. It is shown that such this term is not negligible and generally need to be taken into account in the considerations on the stability of layered materials.
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