|
| |
|
|
Tahová pevnost keramických pěnových materiálů
Řehořek, Lukáš
Full understanding of mechanical properties of highly porous (cellular) ceramic foams is important due to their applications in many ranges of industrial, medical and other applications. There is described technique of mechanical testing in tension of ceramic foam material in this paper. Tested material was based on alumina ceramic and it was manufactured by slurry coating of polyurethane foam. Testing procedure consist from fixation of ceramic foam into aluminum pots by resin. Results and statistical analysis of more than 60 ceramic foam specimens loaded by tension were also described.
|
|
|
Quantification of increasing fracture toughness of glass matrix reinforced by alumina platelets composite
Kotoul, M. ; Pokluda, J. ; Šandera, P. ; Dlouhý, Ivo ; Chlup, Zdeněk ; Boccaccini, A. R.
A borosilicate glass matrix composite containing alumina platelets was considered to investigate toughening mechanisms and crack tip behaviour in dispersion reinforced brittle matrix composites. Fracture toughness was determined applying the chevron notched specimen technique and fractographic analysis was employed to reveal the active toughening mechanisms with increasing content of reinforcement. A roughness-induced shielding effect has been quantified to prove the relation between fracture toughness and fracture surface roughness. Theoretical calculations of the fracture toughness enhancement based on a modified crack deflection model developed by Faber and Evans, combined with the influence of the increase in Young’s modulus, were found to be in good agreement with experimental data. The crack deflection model was further extended to capture a synergy between crack deflection and the contribution of residual stresses to toughening in the investigated composites.
|
|
|
Crack propagation in ceramics laminates with strongly bonded interfaces
Hadraba, Hynek ; Chlup, Zdeněk ; Maca, K. ; Bermejo, R.
Crack propagation through layered composites based on Al2O3 and ZrO2 was studied. The strongly bonded laminates with single-component layers and laminates with two-component layers were prepared via electrophoretic deposition and slip casting respectively. Laminates of different pre-defined thicknesses and composition contained different magnitudes of residual stress. Cracks, produced by an indentation technique, propagated towards layer interfaces deflected towards the interface in the compressed layers and away from the interface in the layers containing tension stress. Changes in the direction of crack propagation were described for the whole range of angles of incidence (0° - 90°). The biggest change in the crack propagation was observed, irrespective of the magnitude of residual stress in the layers.
|
|
|
Crack propagation in strongly bonded Al2O3/ZrO2 laminates
Hadraba, Hynek ; Chlup, Zdeněk ; Maca, K. ; Bermejo, R.
Crack propagation through layered composites based on Al2O3 and ZrO2 was studied. The strongly bonded laminates with single-component layers (A/Z) and laminates with two-component (AtZ/AmZ) layers were prepared via electrophoretic deposition and slip casting respectively. Laminates of different pre-defined thicknesses and composition contained different magnitudes of residual stress. Cracks, produced by an indentation technique, propagated in direction to layer interfaces deflected towards the interface in the compressed layers and away from the interface in the layers containing tension stress. Changes in the direction of crack propagation for the whole range of angles of incidence (0° - 90°) were described. The biggest change in the crack propagation was observed for the angle of incidence 45° for A/Z systems and 32.5° for AtZ/AmZ systems and was ca. 15° and 20° respectively. The change in the crack propagation was independent on magnitude of residual stress in the layers.
|
|
|
Zacelování povrchových trhlin u nanokompozitní keramiky typu Al2O3/SiC
Flašar, Petr ; Dlouhý, Ivo ; Chlup, Zdeněk ; Ando, K.
Indentation strength and self-crack-healing ability were systematically studied using beams containing a semi-elliptical surface crack made by Vickers indentor. Beams of Al2O3/SiC ceramic nanocomposite with a good self-crack-healing ability predetermined for four-point and three-point bending test were prepared by ceramographics techniques. Flexural strength and fracture toughness were determined using three- and four-point bend method. Thermal aging at 1573 K for 1h was applied to heal the samples with indentation pre-cracking. Fractographical analyses using an optical and/or scanning electron microscopy has been carried out to investigate the surface crack behaviour. Very good self-crack healing ability has been proved for surface microcracks having length up to 250 μm and depth no higher than 100 μm.
|
guest ::
