International Standard, ISO 6892-2, Metallic Materials-Tensile Testing: Method of Test at Elevated Temperature maintained that the strain rate variations and test temperature variations can induce the measurement uncertainty of mechanical properties in tensile testing, which will imperil the reliability of tension tests. In this paper, the measurement uncertainties of shrinkage rate or elongation rate in tensile testing cross-section, intermediate temperature embrittlement and strain rate embrittlement are first described experimentally. Second, the fundamental results on the microscopic theory of elastic deformation in metals are briefly mentioned. Then the phenomena of the measurement uncertainties are explained based on the microscopic theory. It is expounded that the elastic deformation of tension tests induces the impurities to segregate to grain boundaries and the relative embrittlement which produces the measurement uncertainties of reduction in area. This work gives a theoretical basis for correcting the present standard method of tension testing to avoid the measurement uncertainty of reduction in area.
In the middle of last century, some scientists discovered grain-boundary anelastic relaxation (GAR) peaks by means of torsional pendulum. Later, various models about the origin of GAR peaks are established through further research. However, its micro-mechanism is still unclear. Recently, according to the results of solute grain boundary segregation or dilution caused by elastic stress, a micro-mechanism of GAR which is grain-boundary absorbing or emitting vacancies has been proposed. Then, the equilibrium equations and the kinetic equations of GAR are established, and the process of GAR is expressed analytically. Furthermore, it has successfully elaborated the intermediate temperature embrittlement peak movement which exists widely in metals. Those developments of GAR theory are reviewed in the present paper.
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