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620.178.72 One of the most widely used structural materials in nuclear power is Zr-1%Nb alloy. However, its mechanical properties have not been investigated to a sufficient extent. This applies primarily to the strength and strain characteristics at high strain rates and under high impact loads. This form of loading of the materials and structures of nuclear power plants occurs in emergency situations [1, 2], which usually arise at operating and increased temperatures.The purpose of the present research was to study the mechanical properties of Zr-1% Nb alloy over a wide range of strain rates and temperature.Mechanical tests on the uniaxial stretching of Zr-l%Nb alloy were carried out in the strain-rate range from 2.5-10 -3 to 8-104 see -1 and over a 20-700~ temperature range. The specimens were made from alloy of standard chemical composition, obtained using technology developed in industry, and were not subjected to any additional heat treatment. Because of the need to ensure a quasi-static uniaxial stress state at a strain rate > 103 sec -l [3], in tests with ~ = 2.5.10 -3-6.2.103 sec -I we used specimens with a working section of length l = 5 mm and diameter d 0 = 2.5 mm. Investigations show [4] that these dimensions and shape of the specimen guarantee a uniaxial stress over a working length of 2.8 mm, in which connection, for this rate, fracture occurs in the middle of the working section with a well-developed neck. Tests at higher strain rates of 8-10'* see -l were made using specimens the working length of which was 0.5 mm and the diameter 2.5 mm. A reduction in the length leads to the formation of a nonuniaxial stress state in the specimen. However, the use of the well-developed method described in [5] enabled us to convert characteristics measured in a nonuniaxial stress state to the characteristics of a uniaxial stress state.Tests at a strain rate from 2.5.10 -3 to 0.6 see -I were made on ZDt0/90 and P-1246 machines; I00 sec -1 on electromagnetic equipment [6] and 3000 sec-l and above (high-rate stretching) on magnetic-impulse equipment [7]. We recorded load-time P(t) oscillograms, from which we constructed stress-strain o(t) diagrams. The systematic error in determining the strength characteristics was 4% and the systematic error in determining the plasticity characteristics was 5%.For high-rate stretching of the specimens at an elevated temperature we used the Hopkins composite rod scheme [8], based on magnetic-impulse equipment. In tests using this scheme (Fig. 1) the specimen was placed in a vacuum chamber between two elastic rods and loaded by generating an elastic wave in the transmitting rod, which, having passed through the specimen and deformed it, was recorded by the rod-dynamometer. This method enabled high-rate stretching of the specimens in a vacuum to be carried out, avoiding oxidation of the specimens at an elevated temperature, where the semiconductor strain gauges of the dynamometer were situated at a safe distance from the heated specimen and were protected by additional special co...
620.178.72 One of the most widely used structural materials in nuclear power is Zr-1%Nb alloy. However, its mechanical properties have not been investigated to a sufficient extent. This applies primarily to the strength and strain characteristics at high strain rates and under high impact loads. This form of loading of the materials and structures of nuclear power plants occurs in emergency situations [1, 2], which usually arise at operating and increased temperatures.The purpose of the present research was to study the mechanical properties of Zr-1% Nb alloy over a wide range of strain rates and temperature.Mechanical tests on the uniaxial stretching of Zr-l%Nb alloy were carried out in the strain-rate range from 2.5-10 -3 to 8-104 see -1 and over a 20-700~ temperature range. The specimens were made from alloy of standard chemical composition, obtained using technology developed in industry, and were not subjected to any additional heat treatment. Because of the need to ensure a quasi-static uniaxial stress state at a strain rate > 103 sec -l [3], in tests with ~ = 2.5.10 -3-6.2.103 sec -I we used specimens with a working section of length l = 5 mm and diameter d 0 = 2.5 mm. Investigations show [4] that these dimensions and shape of the specimen guarantee a uniaxial stress over a working length of 2.8 mm, in which connection, for this rate, fracture occurs in the middle of the working section with a well-developed neck. Tests at higher strain rates of 8-10'* see -l were made using specimens the working length of which was 0.5 mm and the diameter 2.5 mm. A reduction in the length leads to the formation of a nonuniaxial stress state in the specimen. However, the use of the well-developed method described in [5] enabled us to convert characteristics measured in a nonuniaxial stress state to the characteristics of a uniaxial stress state.Tests at a strain rate from 2.5.10 -3 to 0.6 see -I were made on ZDt0/90 and P-1246 machines; I00 sec -1 on electromagnetic equipment [6] and 3000 sec-l and above (high-rate stretching) on magnetic-impulse equipment [7]. We recorded load-time P(t) oscillograms, from which we constructed stress-strain o(t) diagrams. The systematic error in determining the strength characteristics was 4% and the systematic error in determining the plasticity characteristics was 5%.For high-rate stretching of the specimens at an elevated temperature we used the Hopkins composite rod scheme [8], based on magnetic-impulse equipment. In tests using this scheme (Fig. 1) the specimen was placed in a vacuum chamber between two elastic rods and loaded by generating an elastic wave in the transmitting rod, which, having passed through the specimen and deformed it, was recorded by the rod-dynamometer. This method enabled high-rate stretching of the specimens in a vacuum to be carried out, avoiding oxidation of the specimens at an elevated temperature, where the semiconductor strain gauges of the dynamometer were situated at a safe distance from the heated specimen and were protected by additional special co...
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