Progress in the theory of grain boundary anelastic relaxation

The International Organization for Standardization Technical Committee for Metallic Materials—Tensile Testing stated in 2011 that temperature and strain rate variations would induce a change in the results of tensile tests, termed as the measurement uncertainty of tensile mechanical properties in metals. The uncertainty means that the tensile testing results of a specimen at a temperature and strain rate are not the original mechanical properties possessed prior to the testing. Hence, since the time of Galileo the results of tensile testing have been incorrectly interpreted as the original mechanical properties of specimens, thereby forming a paradox. At the turn of the 21st century, the micro-theory of metallic elastic deformation was proposed, identifying that a change in microstructure at atomic level could occur during elastic deformation, leading to a change in the concentration of solute (impurity) at grain boundaries/around dislocations. The micro-theory has been used to explain the mechanism of the measurement uncertainty. Different tensile temperatures and strain rates correspond to different durations of elastic deformation during tensile testing, different concentrations of solute at grain boundaries/dislocations, and thus different mechanical properties. On this basis, a new technology system of tensile testing is suggested, i.e., a “mechanical property–tensile strain rate” curve at a given test temperature can be used to evaluate the original mechanical property. The higher the strain rate is, the closer the property on the curve is to the original property. Therefore, to determine the original mechanical property of the tested metal, a sufficiently high strain rate is required. The curve can also characterize the property variation of the tested metal in service with the service time. In addition, the property characterized by a point on the curve can represent the property of the tested metal when processing-deformed with the corresponding strain rate. As an example of the application of the new technology system, the property of high-entropy alloys is represented with a curve. The results show that the new technology system could change the conceptual framework and testing technology system of metallic mechanics.

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Measurement uncertainty of metallic ductility in tensile tests: intermediate temperature embrittlement and strain rate embrittlement

Tingdong¹,

Liu²,

Hong-Yao³

et al. 2014

Acta Phys. Sin.

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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.

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Progress in the theory of grain boundary anelastic relaxation

Cited by 3 publications

References 28 publications

The measurement uncertainty of reduction in area of metals in tensile testing system

The measurement uncertainty of reduction in area of metals in tensile testing system

Measurement Uncertainty and Representation of Tensile Mechanical Properties in Metals

Measurement uncertainty of metallic ductility in tensile tests: intermediate temperature embrittlement and strain rate embrittlement

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