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 Si 3 N 4 are chosen. It is shown that surface flaws control the strength of the investigated springs.
The Weibull distribution is the most widely used function in the reliability analysis and structural design of dental ceramics; however, it is still unclear whether Weibull distribution is always the most suitable one. With wide applications of dental ceramics, a special attention has been paid in discriminating their strength distributions. In this paper, three versatile functions, involving normal, log-normal and Weibull distributions, are applied to the analysis of ten strength data sets of dental ceramics with different compositions and the results are compared in terms of the Akaike information criterion and the Anderson-Darling test. It reveals that various microstructures and compositions in the investigated dental ceramics cause their strength distributions deviated from the Weibull distribution. The influence of microstructure induced fracture properties (multiple-modal flaw size distribution, R-curve behavior and subcritical crack growth) on strength distributions is discussed.
A PVDF polymer has very good strength, toughness and piezoelectric properties and is nowadays used as the film in strain sensors, mechanical actuators, energy harvesters and artificial muscles. Furthermore, PVDF polymer is used as the fiber in hollow fiber membranes for filtration applications. This article introduces the manufacturing of solid PVDF fibers by a wet spinning process and investigates the effects of the process parameters (i.e. drawing temperatures and drawing ratios on the first and second bath) on macroscopic properties (i.e. fiber linear density, fiber shape, density, porosity, strength and elongation) of solid wet-spun PVDF fibers. Increasing the drawing ratio at the first region of the wet spinning of the PVDF fiber increases the porosity. However, if the drawing is performed at the second drawing bath, the porosity of the PVDF fibers remains almost same. The slopes of the strength vs. drawing ratio and elongation vs. drawing ratio curves increase if the drawing is performed at the second drawing bath. The drawing ratio at the first bath does not affect the tensile properties of fibers, such as tensile strength and elongation. Information about the relationships between the process parameters and macro properties of PVDF fibers is very important so that PVDF fibers with the required properties can be produced with a wet spinning process by setting the correct process parameters.
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.
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.
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