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Fatigue damage prediction of short edge crack under various load: Direct Optimized Probabilistic Calculation
Krejsa, M.; Seitl, Stanislav; Brožovský, J.; Lehnert, P.
2017 - English
Fatigue crack propagation depends on a number and value of stress range cycles. This is a time factor in the course of reliability for the entire designed service life. Three sizes are important for the characteristics of the propagation of fatigue cracks - initial size, detectable size and acceptable size. The theoretical model of a fatigue crack progression can be based on a linear elastic fracture mechanics (uses Paris-Erdogan law). Depending on location of an initial crack, the crack may propagate in structural element (e.g. from the edge or from the surface under various load) that could be described by calibration functions. When determining the required degree of reliability, it is possible to specify the time of the first inspection of the construction which will focus on the fatigue damage. Using a conditional probability and Bayesian approach, times for subsequent inspections can be determined based on the results of the previous inspection. For probabilistic modelling of a fatigue crack progression was used the original and a new probabilistic method - the Direct Optimized Probabilistic Calculation ('DOProC'), which uses a purely numerical approach without any simulation techniques or approximation approach based on optimized numerical integration. Compared to conventional simulation techniques is characterized by greater accuracy and efficiency of the computation.
Keywords:
fatigue; crack propagation; calibration function
Available at various institutes of the ASCR
Fatigue damage prediction of short edge crack under various load: Direct Optimized Probabilistic Calculation
Fatigue crack propagation depends on a number and value of stress range cycles. This is a time factor in the course of reliability for the entire designed service life. Three sizes are important for ...
Effect of alloying and thermal processing on mechanical properties of tial alloys
Chlupová, Alice; Heczko, Milan; Obrtlík, Karel; Beran, Přemysl; Kruml, Tomáš
2017 - English
Two -based TiAl alloys with 7 at.% of Nb, alloyed with 2 at.% Mo and 0.5 at.% C, were studied. A heat treatment leading to very fine lamellar microstructure was applied on both alloys. Microstructure after the heat treatment was described and mechanical properties including fatigue behaviour were measured. The as-received material alloyed with C possesses high strength and very limited ductility, especially at RT. After application of selected heat treatment it becomes even more brittle; therefore, this process could be considered as not appropriate for this alloy. On the contrary, in the case of Mo alloyed material, both strength and ductility are improved by the heat treatment at RT and usual working temperature (~750 °C). Presence of the phase is responsible for this effect. The selected heat treatment thus can be an alternative for this alloy to other thermomechanical treatments as high temperature forging.
Keywords:
Fatigue; Heat treatment; Lamellar microstructure; Mechanical properties; TiAl alloys
Available at various institutes of the ASCR
Effect of alloying and thermal processing on mechanical properties of tial alloys
Two -based TiAl alloys with 7 at.% of Nb, alloyed with 2 at.% Mo and 0.5 at.% C, were studied. A heat treatment leading to very fine lamellar microstructure was applied on both alloys. Microstructure ...
Theory-guided design of novel Fe-Al-based superalloys
Friák, Martin; Holec, D.; Jirásková, Yvonna; Palm, M.; Stein, F.; Janičkovič, D.; Pizúrová, Naděžda; Dymáček, Petr; Dobeš, Ferdinand; Šesták, Pavel; Fikar, Jan; Šremr, Jiří; Nechvátal, Luděk; Oweisová, S.; Homola, V.; Titov, Andrii; Slávik, Ondrej; Miháliková, Ivana; Pavlů, Jana; Buršíková, V.; Neugebauer, J.; Boutur, D.; Lapusta, Y.; Šob, Mojmír
2017 - English
Our modern industrialized society increasingly requires new structural materials\nfor high-temperature applications in automotive and energy-producing industrial\nsectors. Iron-aluminides are known to possess excellent oxidation and sulfidation\nresistance as well as sufficient strength at elevated temperatures. New Fe-Al-based\nmaterials will have to meet multiple casting, processing and operational criteria\nincluding high-temperature creep strength, oxidation resistance and room-temperature\nductility. Such desirable combination of materials properties can be achieved in multi-phase\nmulti-component superalloys with a specific type of microstructure (the matrix contains\ncoherent particles of a secondary phase - a superalloy microstructure). In order to design\nnew Fe-Al-based superalloys, we employ a state-ofthe-art theory-guided materials design\nconcept to identify suitable combinations of solutes.
Keywords:
superalloys; ab initio; materials design; Fe-Al
Available at various institutes of the ASCR
Theory-guided design of novel Fe-Al-based superalloys
Our modern industrialized society increasingly requires new structural materials\nfor high-temperature applications in automotive and energy-producing industrial\nsectors. Iron-aluminides are known to ...
Crack Resistance Characterization in TiAl Intermetallics with Enhanced Toughness
Dlouhý, Ivo; Stratil, Luděk; Fukutomi, H.; Hasegawa, M.
2017 - English
The paper is focused on the analysis of the role of lamellar microstructure in fracture performance of model TiAl intermetallic compound. Coarse lamellar colonies and, at the same time, fine lamellar morphology were prepared by compressive deformation at 1553 K (region of stable alpha phase in TiAl equilibrium diagram) followed by controlled cooling to 1473 K (region of alpha+gamma phase) with delay on this temperature and then cooling down. The fracture toughness was evaluated by means of chevron notch technique. In addition, because of enhanced toughness, crack resistance curves were obtained by load - unload technique of pre-racked beams, namely in two directions of crack propagation relative to lamellar structure. Extensive development of shear ligament toughening mechanism was observed in fracture surfaces leading to quite good fracture toughness thanks to the heat treatment applied.
Keywords:
Titanium aluminides; Intermetallics; Fracture micromechanisms; Shear ligament toughening; Fracture toughness; Crack resistance
Available at various institutes of the ASCR
Crack Resistance Characterization in TiAl Intermetallics with Enhanced Toughness
The paper is focused on the analysis of the role of lamellar microstructure in fracture performance of model TiAl intermetallic compound. Coarse lamellar colonies and, at the same time, fine lamellar ...
Effect of residual stresses on the fatigue lifetime of railway axle
Hutař, Pavel; Pokorný, Pavel; Poduška, Jan; Fajkoš, R.; Náhlík, Luboš
2017 - English
The operation of railway axles should fulfill at least two main demands: safety and low operation costs. A significant part of operation costs is given by the length of regular inspection intervals which should reveal potential fatigue cracks in railway axle. The detection of cracks is of a probabilistic nature, therefore their detection is not ensured in all cases. For the safe operation of trains, an existence of potential initial crack should be considered on the axle surface and residual fatigue lifetime should be conservatively determined for this case. Reliable procedure of residual fatigue lifetime estimation should take into account real axle geometry, material characteristics and loading of the railway axle. This paper shows methodology for determination of residual fatigue lifetime (RFL) based on the fracture mechanics approach, taking into account real spectrum of the loading cycles, existence of press-fitted wheels and surface residual stresses given by the thermo-mechanical surface treatment of the railway axle. It is demonstrated that the effect of the residual stresses is significant and should not be neglected in the numerical estimation of residual fatigue lifetime of the axle.
Keywords:
Railway axle; residual fatigue lifetime; residual stresses; inspection intervals; numerical simulation
Available at various institutes of the ASCR
Effect of residual stresses on the fatigue lifetime of railway axle
The operation of railway axles should fulfill at least two main demands: safety and low operation costs. A significant part of operation costs is given by the length of regular inspection intervals ...
Method of Threshold Stress Determination for a Local Approach to Cleavage Fracture
Kotrechko, S.; Gryshchenko, V.; Kozák, Vladislav; Dlouhý, Ivo
2017 - English
The contribution is focused on a new methodology description for determination of threshold stress sigma th, as the third parameter in Beremin local approach to cleavage fracture that is using three-parameter Weibull statistics. Nature of the methodology lies in tensile testing of rounded notched specimens at liquid nitrogen temperature and corresponding calculations. Reactor pressure vessel steel was chosen as an example for the illustration.
Keywords:
Cleavage; Fracture; Local approach; Threshold stress
Available at various institutes of the ASCR
Method of Threshold Stress Determination for a Local Approach to Cleavage Fracture
The contribution is focused on a new methodology description for determination of threshold stress sigma th, as the third parameter in Beremin local approach to cleavage fracture that is using ...
HYDROGENATION OF CHOSEN MgMXN INTERMETALLICS (X=Al, Ga, In, Si, Sn)
Čermák, Jiří; Král, Lubomír; Roupcová, Pavla
2017 - English
Hydrogen sorption in chosen intermetallics MgmXn (Mg17Al12 , Mg2Ga, mixture of beta-Mg-In phases, Mg2Si and Mg2Sn) formed by magnesium and elements from the 13 th (X: Al, Ga, In) and 14 th (X: Si, Sn) groups was studied between the room temperature and T = 350 °C. Hydrogen pressure p varied from 10-3 MPa to 6 MPa.\nHydrogen solubility in alpha phase (solid solution of hydrogen in MgmXn before the hydride phase was nucleated) was close to hydrogen solubility in pure Mg. Concentration cH of hydrogen solved in Mg m X n depended linearly on pressure p , dependence of cH on temperature T was relatively weak. MgH2 was the main hydrogen storage phase in all the compounds MgmXn . Nucleation of MgH2 at 350 °C was observed at pressure above approximately 1 MPa in Mg17Al12 and above 2 Ma in other compounds. Maximum values of c H in hydride-containing compounds MgmXn detected at T = 350 °C depended on the stability of MgmXn .
Keywords:
Hydrogen; hydrogen storage; Mg alloys; hydrogen solubility; MgH2
Available at various institutes of the ASCR
HYDROGENATION OF CHOSEN MgMXN INTERMETALLICS (X=Al, Ga, In, Si, Sn)
Hydrogen sorption in chosen intermetallics MgmXn (Mg17Al12 , Mg2Ga, mixture of beta-Mg-In phases, Mg2Si and Mg2Sn) formed by magnesium and elements from the 13 th (X: Al, Ga, In) and 14 th (X: Si, Sn) ...
HYDROGEN SORPTION BEHAVIOR OF CHOSEN BINARY MAGNESIUM-CONTAINING INTERMETALLICS
Čermák, Jiří; Král, Lubomír; Roupcová, Pavla
2017 - English
Hydrogen absorption in chosen binary Mg-X (X-Al, Ga, In, Si and Sn) intermetallics was studied. These compounds are prospective as additives in other Mg-based hydrogen storage materials. From this point of view it is desirable to know the hydrogen solubility in Mg-X and their resistivity against hydride formation. The present study was carried out at temperatures up to 623 K.
Keywords:
Hydrogen storage; magnesium alloys; Mg-based intermetallics
Available at various institutes of the ASCR
HYDROGEN SORPTION BEHAVIOR OF CHOSEN BINARY MAGNESIUM-CONTAINING INTERMETALLICS
Hydrogen absorption in chosen binary Mg-X (X-Al, Ga, In, Si and Sn) intermetallics was studied. These compounds are prospective as additives in other Mg-based hydrogen storage materials. From this ...
Influence of the Upper Die and of the Indenter Material on the Time to Rupture of Small Punch Creep Tests
Andrés, D.; Dymáček, Petr; Lacalle, R.; Álvarez, J. A.
2017 - English
The Small Punch Creep test has proven to be a suitable technique for assessing the\nproperties of in-service components. It is a reliable, efficient and cost-effective test for predicting\nthe behaviour of the material. The aim of this paper is to analyse the influence of different factors\non the Small Punch Creep (SPC) tests. The influence of the specimen clamping has been studied,\nexperimentally and by means of finite element models on different materials. In the analysed\nconditions, it has been proven that the influence of the upper die on the tests results is generally\nrelatively insignificant, even in the absence of upper die.\nFurthermore, the use of different materials at the punch has also been analysed. In order to achieve\nthis goal, SPC tests have been carried out on two light alloys (AZ31 and AlSi9Cu3) at 473 and\n523K. Three different balls have been employed: ceramic, tungsten-carbide and steel balls. It has\nbeen proven that for the creep ductile alloy (AZ31), there is no apparent effect on the specimen\nresponse. On the other hand, for the creep brittle alloy (AlSi9Cu3), a different trend of the material\nresponse is shown, dependent on the ball used. As a result, there seems to be a significant influence\nof the friction between the punch and the specimen on the tests results, related to the material\nbehaviour.
Keywords:
small punch test; creep; high temperature; light alloys
Available at various institutes of the ASCR
Influence of the Upper Die and of the Indenter Material on the Time to Rupture of Small Punch Creep Tests
The Small Punch Creep test has proven to be a suitable technique for assessing the\nproperties of in-service components. It is a reliable, efficient and cost-effective test for predicting\nthe ...
Fatigue Crack Initiation in Nickel-Based Superalloy MAR-M247 at High Temperature
Šulák, Ivo; Obrtlík, Karel
2017 - English
The present work is focused on the study of crack initiation during low cycle fatigue (LCF) loading of the second generation nickel-based superalloy MAR-M247 treated with hot isostatic pressing. LCF tests were conducted on cylindrical specimens in symmetrical push-pull cycle under strain control with constant total strain amplitude and strain rate at 800 °C in air atmosphere. Selected specimens were electrolytically polished to facilitate surface relief observations. Crack initiation sites were studied by means of scanning electron microscopy (SEM) in dual beam microscope TESCAN LYRA 3 XMU FESEM equipped with focus ion beam (FIB). The microstructure of the material is characterised by coarse dendritic grains with numerous carbides and small casting defects. The average grain size was 2.1 ± 0.3 mm. Fractographic analysis revealed the fatigue crack initiation sites and their relation to the casting defects and material microstructure. Casting defects, carbide inclusions and interdendritic areas were found to be important crack nucleation sites. Specimens’ surface observations revealed the formation of pronounced surface relief with short worm-like markings. Fatigue crack initiation in these places is documented and discussed.
Keywords:
Fatigue crack initiation; Focus ion beam; MAR-M247; Surface relief
Available at various institutes of the ASCR
Fatigue Crack Initiation in Nickel-Based Superalloy MAR-M247 at High Temperature
The present work is focused on the study of crack initiation during low cycle fatigue (LCF) loading of the second generation nickel-based superalloy MAR-M247 treated with hot isostatic pressing. LCF ...
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