Small specimen testing – ASTM approach M P Metcalfe ASTM Symposium on Graphite Testing for Nuclear Applications: The Significance of Test Specimen Volume and Geometry and the Statistical Significance of Test Specimen Population September 2013, Seattle

Background Graphite characterisation and measurement can be undertaken using standards developed by ASTM. The majority of these standards have been developed specifically for graphite by the Petroleum Products and Lubricants Committee under Subcommittee D02.F0 Manufactured Carbon and Graphite Products. Some additional standards applicable to graphite have been developed by the Advanced Ceramics and Thermal Measurements Committees. Historically, the graphite manufacturing industry has been the principal driver behind the development of graphite standards. More recently, standards have been modified and new standards developed to meet the needs of the nuclear industry. ASTM standard guide D was developed to address issues associated with measurements on small graphite specimens.

Background

Overview of guide Current standards developed with the objective of optimising the method of measurement in the absence of any constraints on test sample production. Without exception, these standards either specify limits on the ratio between test sample dimension and particle size and/or prescribe test sample geometries and size ranges. The default position for any user should be to follow these standards exactly as described. However, in some applications, available test material or experiment design constraints on test sample sizes may result in non-compliance. Objective of guide is to provide advice on how the application of selected standards under non-compliant conditions can be tested for suitability.

General guide principles (1) The default position for any user should be to follow existing standards exactly as described. Some specimen geometry and volume constraints may be set by a particular measurement technique and therefore apply to any test material. However, in some cases, constraints may depend upon the microstructure and composition of the material.

General guide principles (2) For non-compliant testing: the user must specify the level of accuracy required and tolerable uncertainties associated with the measured properties

General guide principles (2) For non-compliant testing: the user must specify the level of accuracy required and tolerable uncertainties associated with the measured properties the qualifying measurement criteria must be demonstrated using representative material in a manner compliant with the ASTM standard

General guide principles (2) For non-compliant testing: the user must specify the level of accuracy required and tolerable uncertainties associated with the measured properties the qualifying measurement criteria must be demonstrated using representative material in a manner compliant with the ASTM standard measurements should be repeated on the same material progressively reducing the volume/size to bound the target sample size and geometry

General guide principles (2) For non-compliant testing: the user must specify the level of accuracy required and tolerable uncertainties associated with the measured properties the qualifying measurement criteria must be demonstrated using representative material in a manner compliant with the ASTM standard measurements should be repeated on the same material progressively reducing the volume/size to bound the target sample size and geometry results should be analysed either to demonstrate that method can be extended to smaller test sample sizes or that the method can be applied with corrections

General guide principles (2) For non-compliant testing: the user must specify the level of accuracy required and tolerable uncertainties associated with the measured properties the qualifying measurement criteria must be demonstrated using representative material in a manner compliant with the ASTM standard measurements should be repeated on the same material progressively reducing the volume/size to bound the target sample size and geometry results should be analysed either to demonstrate that method can be extended to smaller test sample sizes or that the method can be applied with corrections test specimens should be retained as checks/secondary standards

Measurement methods covered by first issue of guide Bulk density by physical measurement (C559) Electrical resistivity (C611) Modulus of elasticity and fundamental frequencies by sonic resonance (C747) Sonic velocity for use in obtaining Young’s modulus (C769) Linear thermal expansion of solid materials with a push-rod dilatometer (E228) Thermal diffusivity by the flash method (E1461)

Development of guide and more detailed considerations concerning specimen size Guide will be extended to include other measurements (e.g. strength) Guide will be updated to include refinements to existing advice

Development of guide and more detailed considerations concerning specimen size Guide will be extended to include other measurements (e.g. strength) Guide will be updated to include refinements to existing advice This Symposium provides an opportunity to look in depth at specimen size issues and to identify knowledge gaps The effects of irradiation will not be addressed. Irradiated graphite (at a given dose, irradiation temperature and density) are just a different graphite type.