Chapter 2 Non-contact Measurement of Strains Using Two Orthogonal Sets of Twin “Blue” Lasers R. W. L. Fong and J. Patrick Abstract The pressure tubes for CANDU® (CANDU® (CANada Deuterium Uranium) is a registered trademark of Atomic Energy of Canada Limited.) reactor fuel channels are made of Zr-2.5Nb alloy material. The modelling of fuel channel deformation behavior during accident scenarios, for example, a large break loss-of-coolant accident (LBLOCA), requires knowledge of the high-temperature properties of the pressure tubes. Uniaxial flat specimens are commonly used for tests to obtain the mechanical properties of the material for their response to various types of loads that simulate accident conditions. For CANDU fuel sheathing, made from Zircaloy-4 material, biaxial closed-end burst tests are usually conducted to evaluate their creep and ballooning deformation behavior at high temperatures under high heating rates. Since the Zr-alloy materials oxidize readily at elevated temperatures and their metal properties can be drastically affected, the high-temperature testing of samples from these materials should be conducted in a controlled environment, either in vacuum or surrounded by an inert gas atmosphere. By testing inside such an environment, representative mechanical properties of the metal can, therefore, be obtained with minimal effects from chemical interaction during the test. At Canadian Nuclear Laboratories (CNL), we have developed a specially designed facility for high-temperature testing of uniaxial tensile specimens and biaxial burst specimens inside a sealed chamber. The sample is joule-heated at high heating rates with alternating current. Spot-welded thermocouple on the specimen and a PID controller are used for temperature control. Non-contact measurement of strains on the sample is made continuously, using two orthogonal sets of twin “blue” lasers. The use of blue lasers with a shorter wavelength (UV) than infrared emissions has been demonstrated to allow discernable deformations to be measured while the sample is heated to 1000 ◦C or higher. This paper will briefly describe the novel four-laser measurement technique with two examples to demonstrate strain measurements for the uniaxial test case and the biaxial burst test case both heated to high temperatures. Keywords Four-laser measurement · Fuel sheathing biaxial burst · Pressure tube uniaxial test · High-temperature deformation 2.1 Introduction The thermo-mechanical properties of zirconium-based alloy fuel sheath and pressure tube materials have to be known to properly evaluate their high-temperature response during a large break loss-of-coolant accident (LBLOCA). The mechanical testing of these materials at very high temperatures in a controlled environment using standard commercial test equipment can be restrictive and difficult. Specialized equipment are needed to meet several test requirements. The design and operation of the test facility have to be able to test small and representative specimens over a range of high temperatures and mechanical stress conditions. An inert gas-tight chamber to enclose the specimen is required to isolate the high temperature effects on the material from the effects of chemical interactions (e.g., heavy oxidation or hydriding). The specimen temperature and high heating rates and stress loading are controlled to simulate accident conditions. Strain measurements at high temperatures are required with online acquisition capability without affecting the mechanical behavior of the specimen during the test. Burst behavior of fuel sheath under various accident scenarios has been extensively studied. Under some accident conditions, the fuel sheath deforms as a result of internal pressure and high temperature excursion that can lead to ballooning R. W. L. Fong ( ) · J. Patrick Canadian Nuclear Laboratories, Chalk River, ON, Canada e-mail: randy.fong@cnl.ca; james.patrick@cnl.ca © The Society for Experimental Mechanics, Inc. 2021 M.-T. Lin et al. (eds.), Advancement of Optical Methods & Digital Image Correlation in Experimental Mechanics, Conference Proceedings of the Society for Experimental Mechanics Series, https://doi.org/10.1007/978-3-030-59773-3_2 7
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