Intrinsic failure and non-linear elastic behavior of glasses

Inert failure strains of carefully prepared glass fibers, measured by using the two-point bending technique, are large. For example, the failure strain is about 18% for silica fibers. To convert such high strains to stresses, the strain dependence of the Young’s modulus (i.e., non-linear elastic behavior of glass) has to be taken into account. However, experimental values of modulus for most glasses are available only for low strains (typically <2%). In this paper, we propose that a description of the non-linear elastic behavior of glass up to and including the fourth-order modulus is necessary and adequate for converting intrinsic failure strains to failure strengths. We examine the validity of the proposed formulation by comparing the measured fiber strengths in pure tension to the values calculated – using the proposed formalism – from measured intrinsic failure strains in two-point bending for two glass compositions (silica and E-glass) for which all necessary data are available in the published literature.