LIGO Document G1300798-v1

Photographic and Ultra-Fast Video Imaging of Fracture of Pristine Silica Glass Fibers

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G - Presentations (eg Graphics)
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Modern detectors searching for gravitational waves radiated by astronomical sources operate by measuring the relative positions of massive solids the mirrors of laser interferometers. These mirrors are suspended on thin fibers as pendulums. A critical requirements for these pendulums is ultra-low mechanical loss factors (10-8), and thus low thermal displacement noise. For this reason the mirrors and their suspension fibers are produced from pure silica glass. The mass of the mirrors (test masses) of the largest GW detector aLIGO is 40 kg, where each test mass will be suspended on 4 silica fibers with diameter 400 m. It is known from the literature that silica fibers can exhibit an ultimate breaking stress in excess of 5Gpa. However many factors would significantly reduce the fiber strength. A preliminary study of the fabrication and breaking of flame and laser pulled silica fibers has been performed. For a better understanding of fracture mechanisms we conducted a series of breaking experiments with high speed photography and video imaging. We confirm that our surface preparation procedure (based on flame or laser polishing of the silica stock) allows us to pull fibers with a flawless surface. However, thick fibers (diameter >230m) break mainly at the fiber ends at a much lower stress. The reduction in strength is shown to correlate with heating of the neck and stock area in order to aid in alignment of the fiber prior to testing. Besides the initial fiber breaking (that occurred usually near the thinnest point), an explosive fracture of silica glass is observed, mainly in the heated neck areas. This character of fracture is presumable caused by interaction of thermo-induced mechanical strength and shock elastic waves propagating along fiber after breaking.
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Notes and Changes:
The presentation file contains lot of animation. The animation does not work in pdf file, that is why we have uploaded pptx file as main.
Publication Information:
Talk on 23 International Congress on Glass, Prague, 05 July 2013.

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