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Item type:Publication, Access status: with files , Automated control of stable crack growth for R-curve and rapid v-K-curve measurements(2016-10); ; ; ; A semi-automated technique for controlled crack growth in brittle materials and the simultaneous measurement of R-curve and v-K-curve (subcritical crack growth) is presented. The experimental technique and the evaluation procedure are described in detail. By using bending tests in 3-point and 4-point bending, the technical effort is comparatively low, as the preparation of bending bars is relatively simple. Some experimental results for glass and silicon nitride illustrate the capability of this new method.Publicationtype: Conference Presentation64 25 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Erratum: Intergranular nanostructure effects on strength and toughness of Si3N4 (Journal of the American Ceramic Society (2015) 98:5 (1650-1657) DOI: 10.1111/jace.13484)(Wiley-Blackwell, 2015-09-11); ; ; ; Publicationtype: Journal Article56 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Intergranular nanostructure effects on strength and toughness of Si3N4(Wiley-Blackwell, 2015-04-21); ; ; ; Strength, toughness, microstructure, and atomic adsorption arrangement in silicon nitrides with MgO and RE2O3 additions (RE = La, Gd, Y, Lu) were examined. Mechanical properties were high for La, Gd, and equal La-Lu additions, but surprisingly were progressively lower for Y- and Lu-doped samples. The lower strength and toughness were associated with fewer visible crack deflections and grain bridges. Detailed microstructural analysis of the Lu-doped material revealed a complex intergranular nanostructure with variable Lu content and Si3N4 nanocrystals. Furthermore, the Lu-rich areas showed an extra Lu-adsorption site on the Si3N4 prismatic planes not previously observed in other studies. This inhomogeneous structure was attributed to grain growth impingement and higher viscosity of the Lu-doped oxynitride glass that slows homogenization. The Y-doped material with nearly identical glass viscosity demonstrates intermediate behavior. Finally, substituting half of the Lu2O3 with La2O3 resulted in a homogenous intergranular structure, attributed to a lower viscosity of the oxynitride glass phase, and high mechanical properties. Overall, care must be taken when adapting Si3N4 processing parameters for the smaller ionic radius rare earth dopants such as Lu and Y.Publicationtype: Journal Article87 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Automated control of stable crack growth for R-curve measurements in brittle materialsStable crack advance is required for a reliable crack growth resistance (R-Curve) measurement. In bending experiments, manual control of the mechanical load and observation of the growing crack is still being done by the operator. This work presents an approach to partly and fully automated R-curve measurements, where stable crack growth is achieved solely via computer control. The experimental setup in conjunction with an intelligent control algorithm leads to reliable results, even for brittle materials like alumina ceramics, silicon nitride, and glass. Furthermore, it allows for a novel type of measurement, because the device detects any kind of energy release in the specimen, actually also without visible crack extension. The setup has been used successfully for about 3 years. The operating principle is explained and some of the results are presented exemplarily. The method is realized in 4-point-bending, but can be implemented also for other types of specimen and loading to automatically achieve stable crack growth. © 2012 Society for Experimental Mechanics.Publicationtype: Journal Article86 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Influence of finite notch root radius and optically determined crack length on the measured fracture toughness of brittle materialsWhen measuring the fracture toughness of ceramics, for instance with the Single Edge V-Notched Beam (SEVNB) method, a known problem is given by the finite notch root radius. If this radius is larger than a certain small value of a few micrometers, the measured stress intensity factor is higher than the true intrinsic value. Another problem is that due to technical and physical reasons the optically measured crack length at stable crack growth is smaller than the true crack length, which might lead to an underestimation of the fracture toughness. In the given paper an experimental approach is presented to register these effects quantitatively with stable crack advance and to finally obtain the correct fracture toughness. This is achieved by applying a new computer aided automatic control system for stable crack advance and by analyzing the results in force - displacement and crack length - force diagrams. The used material is zirconia-toughened alumina.Publicationtype: Working PaperScopus© Citations 15 1148 664