|
| |
|
|
Recent Approaches to Brittle Fracture Characteristics of Steels
Dlouhý, Ivo ; Hadraba, Hynek ; Kozák, Vladislav ; Chlup, Zdeněk ; Holzmann, Miloslav
A brief overview of the current approaches for evaluating selected brittle fracture properties of steels relating to fracture resistance of welded joints. A critical analysis of the existing solutions to a singleparameter description of a crack tip stress field, linear-elastic and elastic-plastic fracture mechanics. Two-parameter fracture mechanics as the next development stage of fracture mechanics and impacts of its knowledge on fracture toughness measurement. Master curve for fracture toughness description of steels in the transition region. Local approach as the next fracture mechanics concept enabling prediction of global brittle fracture properties. Application of micromechanical crack tip fracture models (toughness scaling models) for correction of fracture mechanics data in their transfer from a specimen of one geometry to a specimen of another geometry and size (transferability). Evaluation of fracture properties of heterogeneous materials according to the SINTAP procedure.
|
|
|
Fracture behaviour of high-chromium 9% and 14% Cr-Mo and Cr-W steels
Hadraba, Hynek ; Stratil, Luděk ; Kazimierzak, B. ; Fournier, B. ; Dlouhý, Ivo
The paper describes the influence of the microstructure (coming from the chemical composition and extrusion shape) of 9 and 14%Cr- W(Mo)-Ti-Y2O3 ODS steels prepared by mechanical alloying and subsequent hot-extrusion on their impact properties. The chemical composition and corresponding microstructure plays a major role on the impact properties. 9Cr-2W ferritic-martensitic steel present lower upper shelf energy (USE) about 7 J and a lower ductile to brittle transition temperature (DBTT) about -30°C compared to 14Cr-1W ferritic steel one. The transition energy curves of low-activation ferritic 14Cr-1W ODS steel was shifted by about 50°C toward lower temperatures and USE by about 4 J towards higher energies. The extrusion shape also plays a role on the impact properties. The texture caused by the forming process strongly influenced the impact behaviour of the steels. The extensive splitting of the fracture surfaces of plate shaped steel comparing with steels extruded as bar was found.
|
|
|
Assessment of Pressure Vessels Safety
Macurová, K. ; Tichý, R. ; Strnadel, B. ; Dlouhý, Ivo
Conditions of pressure vessels breach are investigated in the present paper. Safety of the modified criteria application of Leak Before Break when a residual stress is found in the vessel material is analysed. Design criterion is based on a critical crack length which must be less than the thickness of the vessel wall. Superposition of residual stress, which occurs in the production of a vessel by impact extrusion, and the hoop stress caused by the internal pressure significantly affects the life and conditions of technical use. Size and character of the distribution of residual stresses were determined experimentally by use of the hole-drilling method. The numerical simulation and mathematical calculations have been carried out applying ANSYS and MATLAB software. The main attention was focused on the application of residual stress in the numerical analysis based on values obtained by the experimental measurements by hole–drilling method.
|
|
|
Methods for evaluation of stability of crack between two isotropic/orthotropic materials
Damborský, Petr
This article deal with problems of cracks in bodies with bimaterial interface. The approaches based on the stress intensity factor (SIF) and the energy release rate (ERR) concepts are presented for isotropic and orthotropic materials. A relation between the mixity of the two fracture modes (I and II) in accordance with the two approaches mentioned is presented. The last part deals with the use two states ψ- integral to determine generalized stress intensity factor.
|
|
|
Fracture behaviour of ceramic laminates with strong linked layers
Chlup, Zdeněk ; Slabáková, Lenka ; Drdlík, D. ; Hadraba, Hynek ; Dlouhý, Ivo
Multi-component ceramics materials having layered structure possess potential to be more convenient than monolithic ones. Depending on design a number of laminated structures can be distinguished. The most common division is by behaviour of layer interface i.e. with strong or weak interfaces. In this contribution the fracture behaviour of the laminates with strong interface allowing creation of residual stresses within layers will be described. Presence of residual stresses can enhance fracture properties. The alumina and zirconia were the components and electrophoretic deposition was used to prepare the laminate. Fracture behaviour was investigated using three point bending test of SEVNB specimens. Fracture surfaces were reconstructed and crack propagation changes were determined. Influence of residual stresses on fracture behaviour was found and described.
|
|
|
Effect of coating on fracture behaviour of ceramic foams under tensile loading
Řehořek, Lukáš ; Dlouhý, Ivo ; Chlup, Zdeněk
Cellular structures are promising type of architecture for a lot of materials whether made of metals, plastic or ceramic. Target applications are those where lightweight, damping and and/or stiff properties are required. With combination of different kinds of materials the foamed composites with favourable mechanical properties can be developed. In case of ceramic foams the main disadvantage – brittleness – can be reduced. For straight forward application of this materials all types of mechanical properties have to be known. The tensile properties of open cell ceramic foam material based on alumina coated by various materials are presented in this paper.
|
|
| |
|
|
Optimization of the initial crack length in consideration of the groove width for wedge splitting test specimen
Seitl, Stanislav ; Klusák, Jan
An optimization of the initiate crack length in view of the width of grips groove of the wedge splitting (WS) specimen is the topic of the contribution. The WS specimens are now started to be used for fracture laboratory testing, especially of quasi-brittle cement-based composites. For the optimization the theory of the general fracture mechanics is used. For the numerical calculation the finite element method and ANSYS software are used. At the end, the optimal crack lengths for various grips widths are discussed and some suggestions are pronounced.
|
guest ::
