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Contribution to the Fracture Behaviour of PM Ledeburitic Steels
Jurči, P. ; Dlouhý, Ivo
The samples made from the Vanadis 6 PM ledeburitic tool steel were surface machined to different quality and heat treated by standard regime of the processing. Three point bending tests were made on processed samples. It was found that the three point bending strength decreased with decreased surface quality. Based on the results it can be suggested that to prevent the cracking of tools in the practice it is essential to make a surface machining (grinding, lapping, polishing) to as high quality as possible.
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Numerical investigation of residual lifetime of the wheel during EN 13262 test
Matušek, P. ; Hutař, Pavel ; Náhlík, Luboš ; Knésl, Zdeněk ; Kunz, Ludvík
In this paper, the experimental set up corresponding to the test unit used for the full-scale fatigue test has been modelled. The numerical method for reliable estimation of residual fatigue lifetime of wheel web tested according to EN 13 262 Standard has been developed. Numerical calculations are based on finite element method utilizing the system ANSYS. The experimentally observed cracks in the wheel web have been taken as the initial crack configuration. Numerical calculations simulating the initial crack growth in the wheel web loaded by experimental set up have been performed. Under assumptions of linear elastic fracture mechanics the residual fatigue life of the cracked wheel has been predicted.
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Influence of surface hardening on fracture behaviour of steels
Dlouhý, Ivo ; Chlup, Zdeněk ; Hadraba, Hynek
The paper is focused on the phenomena associated with fracture in surface layer produced by three different procedures. Standard cementing, nitriding and surface hardening were applied onto surfaces of six low alloy structural steels. For fracture behaviour evaluation Charpy type specimen with U notch were applied the surface of the notch radius was hardened too. The samples were loaded by means of an instrumented impact pendulum. The evaluation and classification of different fracture behaviour modes have been based on evaluation of load – flexure traces supported by fractographic analysis. Knowledge obtained were summarised into general schematics of failure modes. As the most detrimental for the fracture resistance the surface cementing was found. The surface hardening showed the minimal negative effect on crack initiation and relatively small fracture resistance decrease.
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Lomová analýza epoxido-hliníkových spojů vystavených teplotnímu a strukturnímu zatížení
Korbel, J. ; Klusák, Jan ; Knésl, Zdeněk
The paper presents a fracture mechanics approach to estimation of critical load (thermal or structural) of adhesive joints. Attention is focused on failure of test specimens prepared by gluing aluminum plates with a commercial thermosetting adhesive. Residual stresses caused by differences of thermal expansion of the adhesive and adherent are also examined. Classical fracture mechanics does not deal with behavior of a bi-material interface, and therefore an approach based on a generalized stress intensity factor and generalized fracture toughness is employed.
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The Simulation of impact test on R7T steel
Severa, Martin
Charpy impact is dynamic experiment that we detect material behaviour under high loading rates. Charpy impact test is used as method for brittle farcture characterization. In this work material model based on Johnson – Cook equations was used for prediction of the dynamic behaviour of the experimental material. Comparison of numerical solution and data obtained in experimental test is presented.
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Fatigue life and fatigue fracture of nickel-based superalloy Inconel 792-5A at room and at elevated temperatures
Šmíd, Miroslav ; Obrtlík, Karel ; Petrenec, Martin ; Polák, Jaroslav ; Hrbáček, K.
The aim of the present work is to study the effect of temperature on the fatigue life and fracture in cast polycrystalline nickel base superalloy Inconel 792-5A. Surface relief and fracture surface observations help to elucidate fatigue damage mechanism in the material used to produce the most critical component of gas turbines. Fatigue live curves can by approximated by the Manson-Coffin and Basquin law. Special attention was paid to the cyclic strain localisation on the specimen surface. Specimens strained with different strain amplitudes were used for fractographic investigation at each temperature. Both, the surface relief and the fracture surface observations, provide data on fatigue crack initiation. Detailed study of fracture surface topography was performed at all temperatures and different strain amplitudes and typical morphologies are documented. Fatigue damage mechanisms and crack path are discussed in relation to temperature, strain amplitude and crack lenght.
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Interakce mezi Ti-Al-Nb taveninou a Y2O3 kelímky
Barták, Tomáš ; Dlouhý, Antonín ; Dočekalová, Kateřina ; Zemčík, L.
The present paper focuses on interactions between intermetallic melts (Ti-46Al-7Nb-0.7Cr-0.1Si-0.2Ni alloy (at%)) and ceramic crucibles based on the Y2O3 refractory. Different levels of superheat and exposure time are taken into account. Vacuum induction melting (VIM) experiments were performed using the vacuum furnace BALZERS VSG 02. The controlled argon atmosphere inside the furnace volume was kept at the pressure level of 0.133 bar during the melting experiments. The reactions at the melt - crucible interface were studied by means of scanning electron microscopy (SEM) equipped with the energy dispersive x-ray analyzer (EDX). There has been clear benefit when a common refractory like alumina has been replaced by yttria. However, the results obtained in this study show, that the long - term exposure at melting temperatures above 1650°C lead to notable reactions at the interface. We discuss the stability of the melt - ceramic system using principles of thermodynamic equilibrium.
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Interaction between TiAl metl and coated ceramic crucibles
Dočekalová, Kateřina ; Dlouhý, Antonín ; Zemčík, L. ; Fiala, J.
The present work focused on interactions between TiAl melt and coated oxide refractories. Melting experiments were performed in vacuum induction furnace (VIM technology). The attention is given mainly to reaction interfaces between the melt and ceramics, however, the microstructure of the cast alloy is also taken into account. The analysis is performed using scanning electron microscopy (SEM) and EDAX. Experimental results were compared with results of thermodynamic calculations that estimated a probability of chemical reactions at the melt-refractory interface. The results indicate that there is an influence of ceramic coatings on the cast microstructure. The detailed composition of the reaction interface and the explanation of reaction mechanisms based on thermodynamic calculations is presented.
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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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