Confirmation of thin surface residual compressive stress in silica glass fiber by FTIR reflection spectroscopy

• Silica glass under stress shows a shift in the 1120 cm− 1 peak by FTIR reflection.
• The magnitude of the peak shift is proportional to the stress in the glass.
• The method is applicable to silica glass if the thermal history is known.

Recently, a new method of glass strengthening for silica glass fibers was proposed and demonstrated. The method involves the process of surface stress relaxation while the glass fiber is subjected to a tensile stress. Upon release of the applied tensile stress, the glass fiber acquires a residual surface compressive stress which can make the glass fiber stronger. The presence and magnitude of residual surface stress in the fibers were evaluated by observing the permanent bending of 1) fibers that were bent, heat-treated, and released, as well as 2) fibers that were heated while held under a uniaxial tensile stress, released, and then sliced. Direct observation of birefringence due to surface residual stress in the treated fibers was not possible due to the extremely thin surface layer of the residual stress. In this work, the previously evaluated magnitude of residual surface stress formed in silica fibers was confirmed by observing a shift of an IR reflection silica structural band after both bending and uniaxial tensile treatments at a temperature far below the glass transition temperature.