Silica-clad optical fibers are proof tested in tension at levels of 700 MPa or greater to ensure product quality. The flaws passing proof testing generally are assumed to be ideal; however, some of these flaws are associated with refractory particles that are fully or partially submerged on the silica surface. Residual stresses are generated in the silica due to a thermal expansion mismatch between the particles and the host silica. These stresses can affect the crack growth characteristics and lifetime predictions for silica-clad optical fibers.

Residual stresses around refractory particles are quantified using analytical and finite element models. Zirconia particles generate the highest stresses at low aspect ratios. As aspect ratio increases, materials with higher elastic moduli, such as SiC, generate the highest stress levels. The residual stress fields are incorporated into crack stress intensity relations and their effect on optical fiber strength is evaluated for different refractory materials, particle sizes, and particle aspect ratios. The results are compared to the residual stress fields and stress intensity relations for model flaws created by indentation with diamond pyramids.