Relationship of Tensile Strength of Glass Fibers to Diameter

The measured strength of a glass fiber is associated with the special circumstances attending its formation. Experimental evidence is presented which shows that, contrary to generally accepted belief, the strength of a fiber does not depend on fiber diameter. When fibers of different diameter are formed under controlled, nearly identical conditions, the breaking strengths are identical within the experimental limits and there is no significant effect of diameter as such. Summary (1) The properties of glass fibers, including strength, are associated with the special circumstances attending their formation. (2) In the past, fibers of different diameters were inevitably made under different forming conditions; it was found necessary in hand drawing to heat the glass to higher temperatures and to pull faster to obtain fibers of small diameter. (3) In the past, therefore, fibers of different diameters were reported as having different strengths (i.e., breaking stresses, not breaking loads), and this difference was ascribed to diameter as such without considering whether it might be due to different forming conditions. (4) When fibers of different diameter are formed under controlled, nearly identical conditions, the breaking strengths are identical within the experimental limits and there is no significant effect of diameter as such.