Influence of Surface Treatment on Strength Distribution of Vita VMK 68 Dental Porcelains

Weibull distribution function is the most commonly used statistical model for the investigation of mechanical properties of dental ceramics and design process with dental ceramics. However, it is still unclear whether the Weibull distribution function is the most appropriate function for fitting the strength data of dental ceramics with different surface treatments. In this paper, three-point bending test results of feldspathic body porcelain (Vita VMK 68) specimens with four different surface treatments are analysed. According to goodness-of-fit tests (Anderson-Darling test, Kolmogorov-Smirnov test, and Akaike information criterion), it is shown that the type of surface treatment has an important influence on deviation of strength distribution from perfect Weibull statistics. It is concluded that estimation of the most suitable statistical model for Vita VMK 68 is not only a material-dependent but also a process-dependent (machining of the specimens) procedure

Vat Photopolymerization Additive Manufacturing of Functionally Graded Materials: A Review

Functionally Graded Materials (FGMs) offer discrete or continuously changing properties/compositions over the volume of the parts. The widespread application of FGMs was not rapid enough in the past due to limitations of the manufacturing methods. Significant developments in manufacturing technologies especially in Additive Manufacturing (AM) enable us nowadays to manufacture materials with specified changes over the volume/surface of components. The use of AM methods for the manufacturing of FGMs may allow us to compensate for some drawbacks of conventional methods and to produce complex and near-net-shaped structures with better control of gradients in a cost-efficient way. Vat Photopolymerization (VP), a type of AM method that works according to the principle of curing liquid photopolymer resin layer-by-layer, has gained in recent years high importance due to its advantages such as low cost, high surface quality control, no need to support structures, no limitation in the material. This article reviews the state-of-art and future potential of using VP methods for FGM manufacturing. It was concluded that improvements in printer hardware setup and software, design aspects and printing methodologies will accelerate the use of VP methods for FGMs manufacturing

Machine learning assisted material development for lithography-based additive manufacturing of porous alumina ceramics

The transition of applying ceramic additive manufacturing (AM) from prototyping to mass production and from monolithic to multi-material (MM) components can be supported by continual development in materials and processes. Lithography-based ceramic manufacturing (LCM) can be used for MM printing of ceramics with high accuracy by introducing different approaches that enable discrete/smooth multidirectional material transitions. Adaptation of ceramic slurries plays important role for the successful printing and co-sintering. Especially for co-sintering, the shrinkage of the materials must be adapted so that no internal residual stresses occur. Machine learning (ML) offers promising opportunities for development of new materials and optimization of processes in AM by introducing relations between input features and output responses. In this article, ML algorithms were used for the prediction of shrinkage and porosity of alumina samples dependent on input features including material, printing, and thermal processing parameters so that defect-free porous/dense alumina combination can be achieved

Failure probability of ceramic coil springs

Ceramic springs are commercially available and a detailed reliability analysis of these components would be useful for their introduction in new applications. In this paper an analytical and a numerical analyses of the failure probability for coil springs under compression is presented. Based on analytically derived relationships and numerically calculated results, fitting functions for volume and surface flaws will be introduced which provide the prediction of the failure probability of ceramic coil springs with different spring- and material parameters. As an example, typical mechanical properties for Si3N4 are chosen. It is shown that surface flaws control the strength of the investigated springs.Ceramic springs are commercially available and a detailed reliability analysis of these components would be useful for their introduction in new applications. In this paper an analytical and a numerical analyses of the failure probability for coil springs under compression is presented. Based on analytically derived relationships and numerically calculated results, fitting functions for volume and surface flaws will be introduced which provide the prediction of the failure probability of ceramic coil springs with different spring- and material parameters. As an example, typical mechanical properties for Si3N4 are chosen. It is shown that surface flaws control the strength of the investigated springs

Influence of Surface Treatment on Strength Distribution of Vita VMK 68 Dental Porcelains

Weibull distribution function is the most commonly used statistical model for the investigation of mechanical properties of dental ceramics and design process with dental ceramics. However, it is still unclear whether the Weibull distribution function is the most appropriate function for fitting the strength data of dental ceramics with different surface treatments. In this paper, three-point bending test results of feldspathic body porcelain (Vita VMK 68) specimens with four different surface treatments are analysed. According to goodness-of-fit tests (Anderson-Darling test, Kolmogorov-Smirnov test, and Akaike information criterion), it is shown that the type of surface treatment has an important influence on deviation of strength distribution from perfect Weibull statistics. It is concluded that estimation of the most suitable statistical model for Vita VMK 68 is not only a material-dependent but also a process-dependent (machining of the specimens) procedure

Determination of the multiaxial failure criteria for alumina ceramics under tension–torsion test

Failure probability of ceramic components in multiaxial stress state can be predicted using the uniaxial test results (e.g. tension test, 4-point-bending test) when a suitable multiaxial criterion, which introduces the triaxiality of stress state, is known. In this article, tension–torsion tests were performed with alumina (Alsint 99.7) specimens from a standard manufacturer under two different load cases. Next experimental results were compared with the numerically calculated effective volume and effective surface values according to different multiaxial failure criteria. It was concluded that the specimens failed due to surface flaws and the normal stress criterion is the most appropriate criterion for the strength prediction of alumina ceramics under multiaxial stress state. Furthermore, it was shown that the Weibull modulus does not play a big role for the prediction of strength of alumina ceramics