Ceramic structural reliability

Lange FF, Luther EP (1994) Colloidal Processing of Structurally Reliable Si3N4. In Hoffmann MJ, Petzow G (eds) Tailoring of Mechanical Properties of Si3N4 Ceramics. NATO ASI Series E. Vol 276, Kluwer Acad Publ Dordrecht, p 3... 

The use of proven catalyst recipes would greatly curtail development times, and the absence of extraneous material avoids unwanted catalytic effects and enhances thermal stability. The fixation of catalyst on ceramic substrates such as washcoats is a well-known, reliable, and relatively straightforward procedure. The fabrication of complex small-scale ceramic structures is, however, more awkward than for metals or plastics, and they exhibit relatively poor mechanical strength. Furthermore, the porous ceramic nanostructure must be sealed to prevent contact between the reaction medium and coolant. 

Computer modeling of GBs can give considerable insights, but be careful when using older results in the literature. The complexity of ceramic structures and the Madelung problem cause difficulties and some older simulations may not be reliable, in part, because they used too little material in the calculation because of the capabilities of the computers. 

The 38th ICACC hosted more than 1,000 attendees from 40 countries and approximately 800 presentations. The topics ranged from ceramic nanomaterials to structural reliability of ceramic components which demonstrated the linkage between materials science developments at the atomic level and macro level structural applications. Papers addressed material, model, and component development and investigated the interrelations between the processing, properties, and microstructure of ceramic materials. 

In brittle ceramic materials, any strains generated undesirably cannot be relaxed by plastic deformation, and this may often lead to an abrupt fracture under even a small strain this is particularly the case for high-elastic-modulus materials. However, if the elastic modulus can be reduced while retaining the strength, then the strain-to-failure ratio can be increased, thus ensuring structural reliability. 

Recent advances further enhance their commercial potential in metal matrix composites such as aluminum, nickel, and copper ceramic matrix composites, such as alumina, zirconia and silicon nitride and glass ceramic matrix composites such as lithium aluminosilicate. Silicon carbide whiskers increase strength, reduce crack propagation, and add structural reliability in ceramic matrix composites. Structural applications include cutting tool inserts, wear parts, and heat engine parts. They increase strength and stiffness of a metal, and support the design of metal matrix composites with thinner cross sections than those of the metal parts they replace, but with equal properties in applications such as turbine blades, boilers and reactors. 

J. A. DiCarlo, Fibers for structurally reliable metal and ceramic composites. Journal of Metals, 37 [6]. 44-49 (1985). 

N. Nemeth. O. Jadaan, and J.P. Gydcenyesi. Lifetime Reliability Prediction of Ceramic Structures Under Transient Thermomechanical Loads, NASA TP-2005-212505 (2005). 

D.K. Shetty, A.R. Ro.senfield, and W.H. Duckworth (1984), "Statistical Analysis of Size and Stress State Effects on the Strength of an Alumina Ceramic," Methods for A.s.se.ssing the Structural Reliability of Brittle Materials, ASTM STP 844, S.W. Freiman and C.M. Hudson, Eds., American Society for Testing Materials, Philadelphia, 57-80. 

Major objectives of research in the Data Base and Life Prediction project element are understanding and application of predictive models for structural ceramic mechanical reliability, measurement techniques for longterm mechanical property behavior in structural ceramics, and physical understanding of time-dependent mechanical failure. Success in meeting these objectives will provide U.S. companies with the tools needed for accurately predicting the mechanical reliability of ceramic heat engine components, including the effects of applied stress, time, temperature, and atmosphere on the critical ceramic properties. 

O. M. Jadaan, andN. N. Nemeth, Transient Reliability of Ceramic Structures, Fatigue Fracture of Engineering Materials and Structures, Vol. 24, 2001, pp. 475 487. 

S. Rahman, N. N. Nemeth, and J. P. Gyekenyesi, Life Prediction and Reliability Analysis of Ceramic Structures Under Combined Static and Cyclic Fatigue, 1998 ASME Turbo Expo Land, Sea, and Air, Stockholm Sweden, June 2 5, 1998, Paper No. 98 GT 569. 

Wiederhorn, S. M. and Tighe, N. J., Structural reliability of yttria-doped hot-pressed silicon nitride at elevated temperatures. J. Am. Ceram. Soc., 1983, 66, pp. 884-9. 

Fligh-tech ceramics withstand great mechanical stresses even thin structures and sharp edges are feasible with high reliability. This allows connecting the HT cables reliably to the ceramic part of the tubes directly. Many available resin systems bond easily to ceramics. 

The need for reliable estimation of a defect in ceramic products of such a complicated structure as the grinding wheel (Fig. 5.22) follows from the mode of its use, since it can be dangerous to those in its vicinity. At the same time, the cost of the product and the requirement of 100% inspection... 

Especially strength and fracture toughness are essential for structural applications. Therefore, great efforts are made to optimise all preconditions for a reproducible production of reliable Si3N4 ceramics with high strength... 

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