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Heat treatment conditions and their influence on precipitation of Ni4Ti3 phase in Ni-rich NiTi shape memory alloys
Dlouhý, Antonín ; Bojda, Ondřej ; Fiala, J.
The present work deals with a quantitative analysis of Ni4Ti3 precipitates after solution annealing (850°C/30min) and ageing (450°C/1hod) in air or inert argon atmosphere. The attention is given not only to the size of precipitates in the vicinity of grain boundaries and in the grain volume and to the corresponding Ni4Ti3 volume fractions, but also to subsequent martensitic transformations B2-(R)-B19’. Quantitative analysis of transmission electron microscopy micrographs is based on the automatic image processing by means of the Adaptive Contrast Control programme. Martensitic transformations were documented using differential scanning calorimetry. Results indicate a homogeneous precipitation of Ni4Ti3 with the heterogeneous distribution of crystallographic particle variants. A possible influence of the heat treatment environment on Ni4Ti3 precipitation and martensitic transformations is discussed in this work.
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Nízkocyklová únava tvárné litiny s 2,8 % niklu
Tesařová, H. ; Petrenec, Martin ; Pacal, B. ; Musilová, I.
Cast ductile iron with the ferritic matrix alloying with 2.8% Ni was subjected to cycling with constant strain amplitudes and the cyclic stress-strain response and fatigue life were studied experimentally. The original microstructure is documented using light microscope. Fracture surface was studied using scanning electron microscopy. Manson-Coffin and Basquin laws can reasonably approximate the fatigue life data. Fatigue crack initiation from shrinkage cavity is documented.
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Low cycle fatigue of ferritic ductile cast iron with alloying nickel
Tesařová, H. ; Petrenec, Martin ; Pacal, B.
Total strain controlled tests have been performed on cylindrical specimens of ductile cast iron with aim to assess of the fatigue resistance. Cyclic hardening, cyclic stress-strain and fatigue life curves were obtained. The microstructure is documented using light microscope. Fracture surface was studied using scanning electron microscopy. Manson-Coffin and Basquin laws can reasonably approximate the fatigue life data. Fatigue crack initiation close to the surface is documented.
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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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Tahová pevnost keramických pěnových materiálů
Řehořek, Lukáš
Full understanding of mechanical properties of highly porous (cellular) ceramic foams is important due to their applications in many ranges of industrial, medical and other applications. There is described technique of mechanical testing in tension of ceramic foam material in this paper. Tested material was based on alumina ceramic and it was manufactured by slurry coating of polyurethane foam. Testing procedure consist from fixation of ceramic foam into aluminum pots by resin. Results and statistical analysis of more than 60 ceramic foam specimens loaded by tension were also described.
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