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Dynamic fracture toughness determination for inherently brittle materials
Flašar, Petr ; Chlup, Zdeněk ; Dlouhý, Ivo
Dynamic fracture toughness measurement of brittle materials using Charpy impact test. A method of dynamic fracture toughness evaluation of brittle materials using Charpy pendulum machine is presented. For low-speed loading rates a specimen damping technique was developed, in high-speed loading rates regime an eccentric onepoint bending test for DKC evaluation was used. A new technique of time to fracture tf measurement was designed using gold-layer deposition on specimen surface. Analytical and numerical analysis of studied problematic was carried out and compared to experimental data.
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Influence of loading conditions on fracture toughness values determined on ceramics
Chlup, Zdeněk ; Dlouhý, Ivo ; Hadraba, Hynek ; Flašar, Petr ; Řehořek, Lukáš
Fracture toughness is generally an important material characteristic. In structural inherently brittle materials as ceramics and ceramics based composites it plays all the more important role. Therefore exact determination of reliable values of fracture toughness is an important matter. Aim of this paper is to analyse influence of selected parameters (applied technique, specimen dimensions, span length, temperature and loading rate) on fracture toughness values. To fulfil this aim, among others, a statistical analysis based on the normal distribution was undertaken. Some of the effects are connected to the material and some of them to the applied methodology. Those linked to the material are hardly describable by a mathematical formula however gives an outlook on possible general trends. On the other hand the span of supporting rollers is an example of parameter whose influence has been described by mathematical formula.
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Transparent composites with ceramic and glass matrix
Polena, J. ; Dlouhý, Ivo
Nowadays transparent composites with ceramic or glass matrix are one of the most promising opto-mechanical materials. They combine low surface density (for aplications as security windows) with high strength. In addition they restrain the unfavourable brittle nature of ceramics. These facts make them the leading candidates for construction aplications, where also optical transparency is needed. The main mechanisms of stiffening are based on the disipaton of fracture energy on the fibre/matrix interface (interphase respectively). Therefore the focus of research is in optimalisation of the interface (interphase respectively) as well as in endeavours to keep good optical transparency.
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Calculation of the Ceramics Material Parameters from the Testing Destructions of the Heads
Fuis, Vladimír ; Návrat, Tomáš ; Hlavoň, Pavel
This paper deals with increasing of the computation modelling level of the reliability problem of ceramic heads of total hip joint endoprostheses. The solution to this problem was invoked by recent more frequent failures of these heads in clinical practice. Results of computational and experimental modelling have shown a substantial influence of shape deviations in the conical connection between stem and head on the initiation of ceramic head fractures. The fracture probability was evaluated step by step for various macroscopic shape deviations in the conical connection and then for microscopic shape deviations superposed on the macroscopic deviations.
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Fracture Behaviour of Inherently Brittle Materials
Dlouhý, Ivo
The proceedings of workshop on Fracture Behaviour of Inherently Brittle Materials organised within series Brittle Fracture. The support of Czech Science Foundation, project Nr 101/02/0683, and Grant Agency of the Academy of Sciences of the Czech Republic, project Nr. A2041003, is gratefully acknowledged.
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Influence of sample geometry (size) effect on fracture toughness characteristics of brittle materials
Chlup, Zdeněk ; Dlouhý, Ivo
Influence of sample geometry (size) on fracture toughness characteristics of brittle materials. The fracture toughness is an important characteristic for structures design even more when inherently brittle material is used. Ceramics materials are those ones where knowledge of exact fracture resistance is crucial and frequently lack of this knowledge can disqualify such material for application in a given component. Over last few years a big effort was paid in investigation in this field. Recently a standardized methodology for fracture toughness evaluation was introduced. However there are many restrictions, mostly in geometrical requirements, and often it is difficult to reach them especially when new material is developed. Data obtained from different geometries of specimen and/or loading conditions time to time it is necessary to compare. The paper attempts to reveal questionable points when data from various sources are compared.
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