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ASTM C1683-2008 Standard Practice for Size Scaling of Tensile Strengths Using Weibull Statistics for Advanced Ceramics

Standard Number:  ASTM C1683-2008
Title:  Standard Practice for Size Scaling of Tensile Strengths Using Weibull Statistics for Advanced Ceramics
Language:  English
Replaced by Standard:  ASTM C1683-2008e1

Execute Date:  2008/1/1
Status:  Withdrawn
International Classification for Standards (ICS)GLASS AND CERAMICS INDUSTRIES>>Ceramics>>Advanced ceramics
Publisher:  American Society for Testing Material (ASTM)
Number of Pages:18P.;A4   


Advanced ceramics usually display a linear stress-strain behavior to failure. Lack of ductility combined with flaws that have various sizes and orientations typically leads to large scatter in failure strength. Strength is not a deterministic property but instead reflects the intrinsic fracture toughness and a distribution (size and orientation) of flaws present in the material. This standard is applicable to brittle monolithic ceramics which fail as a result of catastrophic propagation of flaws. Possible rising R-curve effects are also not considered, but are inherently incorporated into the strength measurements.

Two- and three-parameter formulations exist for the Weibull distribution. This standard is restricted to the two-parameter formulation.

Tensile and flexural test specimens are the most commonly used test configurations for advanced ceramics. Ring-on-ring and pressure-on-ring test specimens which have multi-axial states of stress are also included. Closed-form solutions for the effective volume and effective surfaces and the Weibull material scale factor are included for these configurations. This practice also incorporates size scaling methods for C-ring test specimens for which numerical approaches are necessary. A generic approach for arbitrary shaped test specimens or components that utilizes finite element analyses is presented in Annex A3.

The fracture origins of failed test specimens can be determined using fractographic analysis. The spatial distribution of these strength controlling flaws can be over a volume or an area (as in the case of surface flaws). This standard allows for the conversion of strength parameters associated with either type of spatial distribution. Length scaling for strength controlling flaws located along edges of a test specimen is not covered in this practice.

The scaling of strength with size in accordance with the Weibull model is based on several key assumptions (5). It is assumed that the material is uniform, homogeneous, and isotropic. If the material is a composite, it is assumed that the composite phases are sufficiently small that the structure behaves on an engineering scale as a homogeneous and isotropic body. The composite must contain a sufficient quantity of uniformly-distributed, randomly-oriented, reinforcing elements such that the material is effectively homogeneous. Whisker-toughened ceramic composites may be representative of this type of material. This practice is also applicable to composite ceramics that do not exhibit any appreciable bilinear or nonlinear deformation behavior. This standard and the conventional Weibull strength scaling with size may not be suitable for continuous fiber-reinforced composite ceramics. The material is assumed to fracture in a brittle fashion, a consequence of stress causing catastrophic propagation of flaws. The material is assumed to be consistent (batch to batch, day to day, etc.). It is assumed that the strength distribution follows a Weibull two parameter distribution. It is assumed that the same specific flaw type controls strength in the various specimen configurations. It is assumed that each test piece has a statistically significant number of flaws and that they are randomly distributed. It is assumed that the flaws are small relative to the specimen cross section size. If multiple flaw types are present and control strength, then strengths may scale differently for each flaw type. Consult Practice C 1239 and the example in 9.1 for further guidance on how to apply censored statistics in such cases. It is also assumed that the specimen stress state and the maximum stress are accurately determined. It is assumed that the actual data from a set of fractured specimens are accurate and precise. (See Terminology E 456 for definitions of the latter two terms.) For this reason, this standard frequently references other AST......  

Cross References:ASTM C1161;ASTM C1145;ASTM C1273;ASTM C1211;ASTM C1322;ASTM C1323;ASTM C1499;ASTM C1239;ASTM C1366;ASTM E456;ASTM E6  
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File Size:  273KB
Tile in English:  Standard Practice for Size Scaling of Tensile Strengths Using Weibull Statistics for Advanced Ceramics

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