ASTM C978-2019 pdf free download

ASTM C978-2019 pdf free download.Standard Test Method for Photoelastic Determination of Residual Stress in a Transparent Glass Matrix Using a Polarizing Microscope and Optical Retardation Compensation Procedures
1. Scope
1.1 This test method covers the determination of residual stresses in a transparent glass matrix by means of a polarizing microscope using null or retardation compensation procedures. 1.2 Such residual stress determinations are of importance in evaluating the nature and degree of residual stresses present in glass matrixes due to cord, or the degree of fit, or suitability of a particular combination ofglass matrix and enamel, or applied color label (ACL). 1.3 The retardation compensation method of optically de- termining and evaluating enamel or ACL residual stress sys- tems offers distinct advantages over methods requiring physi- cal property measurements or ware performance tests due to its simplicity, reproducibility, and precision. 1.4 Limitations—This test method is based on the stress- optical retardation compensation principle, and is therefore applicable only to transparent glass substrates, and not to opaque glass systems. 1.5 Due to the possibility of additional residual stresses produced by ion exchange between glasses of different compositions, some uncertainty may be introduced in the value of the stress optical coefficient in the point of interest due to a lack of accurate knowledge of chemical composition in the areas of interest. 1.6 This test method is quantitatively applicable to and valid only for those applications where such significant ion exchange is not a factor, and stress optical coefficients are known or determinable. 1.7 The extent of the ion exchange process, and hence the magnitudes of the residual stresses produced due to ion exchange will depend on the exchange process parameters. The residual stress determinations made on systems in which ion exchange has occurred should be interpreted with those depen- dencies in mind. 1.8 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only. 1.9 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appro- priate safety, health, and environmental practices and deter- mine the applicability ofregulatory limitations prior to use. 1.10 This international standard was developed in accor- dance with internationally recognized principles on standard- ization established in the Decision on Principles for the Development of International Standards, Guides and Recom- mendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
3. Terminology
3.1 Definitions: 3.1.1 For additional definitions of terms used in this test method, refer to Terminology C162. 3.1.2 cord—an attenuated glassy inclusion possessing opti- cal and other properties differing from those ofthe surrounding glass. 3.2 Definitions ofTerms Specific to This Standard: 3.2.1 analyzer—a polarizing element, typically positioned between the specimen being evaluated and the viewer.3.2.2 applied color label (ACL)—vitrifiable glass color decoration or enamel applied to and fused on a glass surface. 3.2.3 polarizer—an optical assembly that transmits light vibrating in a single planar direction, typically positioned between a light source and the specimen being evaluated. 3.2.4 residual stress—permanent stress that is resident in a glassy matrix. Such residual stress may result either from heat treatment above the strain point of the glass, or from differ- ences in thermal expansion between the glass matrix and a cord, applied enamel, or ACL decoration. 3.2.4.1 Discussion—The residual stress may be modified either by heat treatment above the strain point, remelting and homogenizing the glass melt, or by removal of a fired-on ceramic or glass decoration. Residual stress caused by ion exchange may only be relieved by either reexchanging the glass to its original state, removing the exchanged glass from the matrix, or by remelting the exchanged glass and homog- enizing the resulting glass melt. 3.2.5 retardation compensator—an optical device, variants of which are used to quantify the optical retardation produced in transparent birefringent materials, typically positioned be- tween the specimen being evaluated and the analyzer.