|
|
Determination of mechanical properties of light metals and alloys and composites via small punch test
Langer, Jiří ; Dobeš, Ferdinand (referee) ; Válka, Libor (advisor)
The aim of diploma thesis is estimate mechanical properties (yield strength, maximum strength and elongation) of light alloys by means of SPT. For the experiments were selected aluminium alloys (Al 2024, Al 6082 T6, Al 7020 and NASA 398) magnesium alloys (MgZnMn, AZ31, AZ61) and composites (AZ91 + 20 % saffilu a Al + Al4C3). Theoretical part of this thesis is focused on analysis of conversion formulas, which were made from SPT data and conventional testing. Experimental part is dedicated to evaluation of experimental data and critical analysis validity of conversion formulas. In this part of thesis is discused the problematics of reproducibility methodology of SPT.
|
|
|
Application of small punch test for determination of high temperature materials characteristics
Ječmínka, Marek ; Dobeš, Ferdinand (referee) ; Dymáček, Petr (advisor)
Diploma thesis is focused on mechanical properties testing by small punch test and comparison of these properties with mechanical properties obtained by conventional tensile test. Steels P92 and AISI 316L in a shape of discs were tested. There were determined values of mechanical properties, namely yield stress, and ultimate tensile stress, obtained by the small punch test – constant deflection rate in this thesis. Values of initial stress and residual stress were evaluated from relaxation small punch test. Mechanical properties obtained by small punch test – constant deflection rate, and small punch test – relaxation, respectively, are compared with mechanical properties obtained by conventional tensile test, and relaxation tensile test, respectively. There were proposed own empirical relationships for restatement of mechanical properties obtained by small punch test to mechanical properties obtained by conventional tensile test in the thesis. Relatively small agreement of results obtained by small punch test, and conventional tensile test was demonstrated by a comparison. Application of own empirical relationships resulted in better agreement. Very good agreement of results of small punch test – relaxation, and relaxation tensile test was shown by their comparison.
|
|
|
Investigation of Mechanical Properties of Fe3Al-Based Alloys with Vanadium and Carbon Additions by Small Punch Test
Dobeš, Ferdinand ; Dymáček, Petr ; Kratochvíl, P. ; Král, R. ; Çelikyürek, I. ; Torun, O.
Additions of carbon and carbide-forming elements can positively influence high temperature mechanical properties of alloys based on Fe3Al intermetallic compound. In the present study, the effect of vanadium and carbon additions on mechanical properties of Fe3Al-type alloy is investigated by a combination of small punch tests and conventional tensile and compressive tests. The constant-deflection mode of the small punch test is used to estimate the properties and their temperature dependence. The yield force and the maximum force are evaluated from the force vs. deflection dependence and compared with the corresponding quantities resulting from conventional tests. The comparison is discussed in terms of equations suggested previously by Mao and Takahashi. Modifications suggested recently by Garcia et al. are taken into account as well. Fractographic observations of ruptured specimens are performed with scanning electron microscope. Temperature dependence of small punch test quantities is related to the microscopic image of the fracture. Equivalent fracture strain is evaluated from both small punch test data and microscopic observation of fractured specimens. The relation between equivalent fracture strain and small punch fracture energy is examined. Fracture toughness is calculated from the equivalent fracture strain. Temperature dependence of calculated fracture toughness supports the conclusion that the ductility of investigated alloys is not deteriorated by the presence of carbides.
|
|
|
Influence of atmosphere on small punch testing of P91 steel
Dymáček, Petr ; Dobeš, Ferdinand
The small punch testing (SPT) under constant force condition was performed in various atmospheres: air, hydrogen and argon. The material selected for the study was P91 steel and testing temperature 873 K. The effect of atmosphere on the test results such as time to rupture, minimum deflection rate and other parameters was measured and evaluated. The results show that there is not very strong but definite effect of atmosphere on SPT creep rupture time. The longest times to rupture were obtained in hydrogen atmosphere for whole range of tested forces. However the difference between tests in hydrogen and tests in air or in argon diminished with decreasing force and longer time to rupture.
|
|
|
The Influence of Carbon on Small Punch Testing of Niobium-alloyed Iron Aluminide
Dobeš, Ferdinand ; Dymáček, Petr
Iron-aluminium-based alloys are promising candidates for various applications at high temperatures. Unfortunately, creep resistance of these alloys is relatively low. It could be improved by introducing second-phase particles, e. g., by additions of carbon and carbide forming elements. On the other hand, the presence of carbides can influence ductility of the alloys with enhanced creep resistance. In the present study, the effect of niobium and carbon additions on the ductility of a Fe3Al-type alloy is investigated. The constant-deflection mode of the small punch test is used to compare fracture properties and their temperature dependence in the alloy with different amounts of carbon. It is shown that both the fracture energy and the deflection at maximum load are greater in the alloy with the greater carbon and that the ductility is not reduced by the presence of niobium carbides. The ductile-to-brittle transition temperature closely correlates with the temperature of phase transformation from D03 to B2 lattice. This temperature is greater in the alloy with lower carbon owing to greater amount of niobium solved in Fe3Al lattice. Complicated temperature dependence of the yield force can be ascribed to the flow stress anomaly inherent for this type of intermetallic alloys
|
|
|
APPLICATION OF SMALL PUNCH TECHNIQUE FOR EVALUATION OF MECHANICAL PROPERTIES OF ADVANCED METALLIC MATERIALS
Milička, Karel ; Dobeš, Ferdinand
Results of an application of small punch tests on non-steel advanced materials are presented with the aim to show several possibilities of this techique. As representative, three materials were selected: an aluminium alloy 2124Al reinforced with 20 vol.% SiC particulates, a composite of alloy AZ91 with Saffil fibres and an intermetallic alloy based on Fe3Al compound. It is shown that there are some close relationships between the results of the small punch technique and results of creep tests using massive specimens. Advantages of the small punch tests under specific conditions, e.g., if a small amount of testing materials is at disposal, are discussed.
|
|
|
Study of local creep properties of power-plant pipe after long-term service
Milička, Karel ; Dobeš, Ferdinand
A distribution of creep properties in the wall of exposed pipe bend was studied by means of small punch creep. The method consists in a deformation of miniaturized disc specimen by spherical punch under an influence of constant force at elevated temperature. The thickness of the disc applied in the present study was 0.5 mm. The technique is illustrated using results of the tests of pipe bend manufactured from low alloy steel of Czech designation 15128 (DIN equivalent 14MoV 6 3) after service at 540 0C and 17.1 MPa for 104,000 hours. The procedures for estimating creep rupture strength and creep ductility from small punch tests are given.
|
|
| |
|
| |
|
| |
guest ::
