2 Non-contact Measurement of Strains Using Two Orthogonal Sets of Twin “Blue” Lasers 15 Fig. 2.7 Example of four-laser measurements of tube circumference of a fuel sheath sample tested at 600 ◦Cand 700 ◦C (just before tube burst) the tensile direction is then: ε =−(εw +εt), where εw and εt are strains in the width and thickness direction of the sample, respectively. Figure 2.8 shows an example of results of analysis of displacement data measured by four lasers on a flat tensile specimen. In Fig. 2.8a, the four-laser line profiles which have been calibrated using known dimensions (width and thickness) of the new specimen is given in the plot below. Using the calibrated parameters set in the MATLAB routine, the necked dimensions and profile at a particular location on the broken sample can then be precisely analyzed as shown in the plot below in Fig. 2.8b. The laser measured profile is shown to closely match the boundary profile of the fractured surface of the broken samples (top view). 2.4 Conclusion The CNL’s biaxial burst test facility for thermo-mechanical testing at high temperatures has been briefly described. The fourlaser scanning system equipped in this facility has been developed and used successfully for online non-contact measurement of hoop strains in a fuel sheath specimen during creep and ballooning deformation during biaxial burst testing. The four-laser scanning system has also been successfully developed to gather multiple strain measurements at different axial locations of tube that provides an “in situ” means to capture the onset and maximum creep rate during creep and ballooning up until burst at high temperatures. The four-laser scanning technique has also been used successfully for strain measurement on uniaxial flat tensile specimens. Acknowledgments This development and experimental work was funded by Atomic Energy of Canada Limited, under the auspices of the Federal Nuclear Science and Technology Program.
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