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Šíření trhliny v okolí bi-materiálového rozhraní: aplikace na vícevrstvé trubky
Šestáková, Lucie ; Náhlík, Luboš ; Hutař, Pavel ; Knésl, Zdeněk
Layered materials are often used in praxis, primarily because of their better mechanical properties in comparison with properties of individual materials components. During the crack propagation process a configuration of a crack with its tip at the bi-material interface in the structure can occur. It is important to decide if the crack propagates into the second material in this case or not. The step change of material properties at bi-material interface causes that the classical linear elastic fracture mechanics cannot be used. A generalized approach has to be applied. It is to find suitable criteria for determination of the effective values of stress intensity factor for the crack terminating at bi-material interface. Knowledge of these values is important for assessment of service life time such structures.
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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 particles shape on fracture toughness of PP-based particulate composite
Majer, Zdeněk ; Knésl, Zdeněk ; Hutař, Pavel
Polymeric particulate composites with thermoplastics are of great practical importance due to the possibility of modifying mechanical properties and reducing the price/volume ratio of resulting material. The properties of the particles themselves (size, shape, material properties) can have a significant effect on the global behaviour of the composite. Generally, the addition of rigid particles to a polymer matrix will have an embrittling effect on the composite. The presence of the particles significantly influences the cure reaction resulting in the formation of a third phase known as the interphase, which possesses a property distinct from those of the matrix and the particles. The particle-reinforced composite (PP-CaCO3) was modeled as a three-phase material with homogeneously distributed coated particles. The main aim of the article is estimate an effect of the interphase properties on microcrack behaviour.
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Contribution to the fracture toughness of rocks and to its measurement metodology
Vavro, Leona
Considering the fracture rock mechanics in the Czech Republic it is in contrast with the fracture mechanics of concrete, metal, plastic or ceramics relatively less explored area. Presented contribution gives basic knowledge of the development in the methodology of rock fracture toughness measurement in the laboratories of the Institute of Geonics AS CR in Ostrava. The measurement methodology comes out of Publisher reference in International Society for Rock Mechanic. So far, then have been taken samples of basic types of rocks (e. g. granite, sandstone, marble). In the present times there are made the microsections for microscopic study of the mineral – petrology composition and also there are determined basic physical and mechanical properties of rocks. In the following part of the research will be prepared the specimen for the rock fracture toughness measurement, which will be assessed according to the used methodology. The fracture toughness of rocks may be practically used in a wide range of applications; e.g. prediction of the anomalies in the geomechanics processes like the rock bumps.
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