Determination of the deformation deceleration coefficient for calculating the initial effective length of the working part of an annular specimen made of fuel cladding

When studying the plastic properties of metallic materials under tension, the initial calculated length of the sample which affects the final results is of significant importance. In the case of determining the short-term mechanical properties of the materials of fuel cladding pipes using annular samples, calculation of the initial effective length of their working part is rather difficult since the plastic deformation of the annular sample is unevenly distributed along the perimeter. This feature is taken into account using the deformation deceleration coefficient. We present the results of determining the deformation deceleration coefficient for calculation of the initial effective length of the working part of an annular sample made of fuel cladding. An experimental method for determining the coefficient is proposed, taking into account the measurements of the distribution of plastic deformation in certain areas along the perimeter of the sample. The method consists in stretching annular and ovalized samples with marks on the end surface. It is shown that for annular and ovalized specimens from the fuel cladding of a BN-600 reactor, the values of the deformation coefficient and effective length are k = 0.50 ± 0.04 and l₀ = 6.1 ± 0.4 mm, respectively. Analysis of the actual relative deformation of the working parts and comparison with the relative elongation showed that when the ovalized specimens are stretched, the value of the relative plastic deformation is higher than that for annular specimens. The proposed method and the results obtained can be used in determination of the parameters of the materials used in the cladding pipes of the of fast neutron reactors.

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