Pokročilé kovové materiály a kompozity na bázi kovů
http://hdl.handle.net/11012/63735
Thu, 15 Apr 2021 09:03:55 GMT2021-04-15T09:03:55ZClassically determined effective Delta K fails to quantify crack growth rates
http://hdl.handle.net/11012/195859
Classically determined effective Delta K fails to quantify crack growth rates
Vojtek, Tomáš; Pokorný, Pavel; Oplt, Tomáš; Jambor, Michal; Náhlík, Luboš; Herrero, Diego; Hutař, Pavel
Decomposition of the resistance to fatigue crack growth into the intrinsic and extrinsic component is very important for understanding of fatigue failure mechanisms, relation to microstructure and modelling of residual fatigue life. Crack closure for four grades of steel were estimated by the difference between K-max values and the effective Delta K-eff values (measured at the load ratio R = 0.8) corresponding to the same crack growth rate. The results showed that crack closure values obtained by the difference K-max - Delta K-eff were not in agreement with the available crack closure models, both the Newman's model of plasticity-induced closure and the results from finite element analysis. The discrepancies could not be explained by the effect of mean stress, specimen thickness, loading amplitude or T-stress. Therefore, the application of fracture mechanics to fatigue cracks should be revisited. It was pointed out that Delta K-eff may not be a good parameter for quantification of the crack driving force, since the relationship between K-max - K-cl and the cyclic plastic deformation at the crack tip might not be linear.
Sat, 01 Aug 2020 00:00:00 GMThttp://hdl.handle.net/11012/1958592020-08-01T00:00:00ZGeometric Modeling of the Valencia Orange (Citrus sinensis L.) by Applying Bezier Curves and an Image-Based CAD Approach
http://hdl.handle.net/11012/195710
Geometric Modeling of the Valencia Orange (Citrus sinensis L.) by Applying Bezier Curves and an Image-Based CAD Approach
Tinoco Navarro, Hector Andres; Barco, Daniel Ricardo; Buitrago-Osorio, Jaime; Ocampo, Olga
The computer-aided design of fruits are used for different purposes, e.g., to determine mechanical properties by applying engineering simulations, to design postharvest equipment, and to study the natural changes related to the topology. This paper developed a methodology to model Valencia orange (Citrus sinensis), applying Bezier curves and an image-based CAD approach; the orange geometry was designed for different ripening stages. In the modeling process, a 3D construction was carried out using third-order Bezier curves, adjusted to the images taken in orthogonal planes. Four control points defined each profile to compose the geometric pattern of the orange, with geometric errors lower than 3%. Two prediction models were proposed to relate the orthogonal dimensions with a factor size; this means that two dimensions out of three can be predicted. The results showed that the shape ratios kept constant in any ripening stage; however, the radius of curvature evidenced differences in the analyzed shape profiles. The methodological framework presented in the paper might be used to draw other types of citrus fruits. This contribution is a tool to model fruits in 3D, instead of using expensive technological equipment, since it is only necessary to apply computer design tools.
Wed, 29 Jul 2020 00:00:00 GMThttp://hdl.handle.net/11012/1957102020-07-29T00:00:00ZImpact of Antiphase Boundaries on Structural, Magnetic and Vibrational Properties of Fe3Al
http://hdl.handle.net/11012/195711
Impact of Antiphase Boundaries on Structural, Magnetic and Vibrational Properties of Fe3Al
Friák, Martin; Černý, Miroslav; Všianská, Monika; Šob, Mojmír
We performed a quantum-mechanical study of the effect of antiphase boundaries (APBs) on structural, magnetic and vibrational properties of Fe3Al compound. The studied APBs have the {001} crystallographic orientation of their sharp interfaces and they are characterized by a 1/2 < 111 > shift of atomic planes. There are two types of APB interfaces formed by either two adjacent planes of Fe atoms or by two adjacent planes containing both Fe and Al atoms. The averaged APB interface energy is found to be 80 mJ/m(2) and we estimate the APB interface energy of each of the two types of interfaces to be within the range of 40-120 mJ/m(2). The studied APBs affect local magnetic moments of Fe atoms near the defects, increasing magnetic moments of FeII atoms by as much as 11.8% and reducing those of FeI atoms by up to 4%. When comparing phonons in the Fe3Al with and without APBs within the harmonic approximation, we find a very strong influence of APBs. In particular, we have found a significant reduction of gap in frequencies that separates phonon modes below 7.9 THz and above 9.2 THz in the defect-free Fe3Al. All the APBs-induced changes result in a higher free energy, lower entropy and partly also a lower harmonic phonon energy in Fe3Al with APBs when compared with those in the defect-free bulk Fe3Al.
Sun, 01 Nov 2020 00:00:00 GMThttp://hdl.handle.net/11012/1957112020-11-01T00:00:00ZWear of grinding rotors with thermally-sprayed coatings in a high-speed mill
http://hdl.handle.net/11012/188122
Wear of grinding rotors with thermally-sprayed coatings in a high-speed mill
Tkachenko, Serhii; Dvořák, Karel; Jech, David; Slámečka, Karel; Klakurková, Lenka; Paloušek, David; Čelko, Ladislav
In this paper, the erosion behavior of three types of protective thermally-sprayed coatings and non-coated
substrate steel was investigated under semi-industrial test conditions using a laboratory high-speed pin mill
DESI-11. The grinding in the mill was performed by two counter rotors, on which protective coatings were
deposited either by atmospheric plasma spraying (APS) (Cr3C2-NiCr and NiCrBSi coatings) or by high velocity
oxy-fuel (HVOF) process (WC-CoCr coating). The grinding rotors with deposited coatings were used for milling
of the Portland cement, and rotors' weight loss was monitored after milling of 1, 3, 5, 10, and 15 kg of this
material. The lowest weight loss in the mixed impact erosion conditions was exhibited by WC-CoCr coating,
which was followed by Cr3C2-NiCr and NiCrBSi coatings. The greatest material removal on the anterior and the
right lateral faces of rotor pins was a result of erosion damage at high impact angles through surface fatigue wear
and the following failure of protective coatings down to the substrate. In contrast, the top and the left lateral
faces of the pins were subjected mostly to the ploughing and microcutting at oblique impact angles that resulted
in significant erosive damage only if hardness of the pin was lower than that of the Portland cement (Cr3C2-NiCrcoated
and non-coated steel pins). The study also found a significant disproportion between the volumetric wear
losses of various rows of pins of grinding rotors. The central part of the grinding tool consisting of two counter
rotors (both rows of 2-row rotor and a middle row of 3-row rotor) suffered more intensive erosion wear than the
external part (outer rows of 3-row rotor). The design of the mill and the resulting variability in parameters of
milled powder particles at different sites of the grinding tool (such as particle size, particle flux and particle
velocity) were considered as main reasons of this phenomena.
Mon, 15 Oct 2018 00:00:00 GMThttp://hdl.handle.net/11012/1881222018-10-15T00:00:00Z