Flexural Strength by Fractography in Modern Brittle Materials

Abstract

Thin components made from advanced brittle glasses or ceramics are becoming increasingly important due to the widespread adoption of portable consumer products as well as other modern electronic and medical devices. The strength of these brittle materials is traditionally estimated from empirical relationships relating the stress at failure to characteristic lengths derived from the fracture surface's topography. One example is Orr's relationship, σf∙Rm1/2 = Am, which correlates the material strength, σf, to the radius of the “mirror‐mist boundary region,” Rm, through the empirical constant, Am. Although various studies have shown that, for flexural fractures (failed in bending), Am depends on the specimen's geometry, this effect has been generally neglected by arguing that the magnitude of Am is almost constant for thicker specimens. However, we show that this argument cannot be applied to thin geometries, and that by not accounting for the thickness of the sample, the flexural strength will be grossly underestimated. In this work, we introduce an expression based on an iterative fracture mechanics algorithm which yields more accurate estimates of flexural strength for thin brittle components in bending. The accuracy of the model is validated both through flexural strength tests on glass and by comparing our predictions to an extensive literature survey of experimental results.

Reply to “Comment on: ‘Flexural Strength by Fractography in Modern Brittle Materials’”

“…incorrectly forced C = 0, although in both cases C > 10 MPa (i.e., 13.4 and 15.0 MPa respectively when using Equation ). Table I in our paper clearly reports all values of ‘ A’ and the intercept extracted based on this fitting equation, consistent with accepted standards.…”

Comment on: “Flexural Strength by Fractography in Modern Brittle Materials”

“…We read with interest the subject paper by Dugnani and Zednik who state that there is a thickness effect in measuring the mirror constant. This effect has far‐reaching consequences in failure analysis if it is correct.…”

Analytical model of dynamic crack evolution in tempered and strengthened glass plates

“…This model is conceptually similar to the method employed by Dugnani and Zednik (2013) to predict the mist formation in glass samples fractured in bending. However, significant modifications help accommodate the more complex boundary conditions imposed by the parabolic residual stress profile.…”

“…Previously, Dugnani and Zednik (2013) presented a crack evolution model to estimate the dynamic SIF at the tip of a crack in an annealed plate loaded in bending. The model was found to accurately describe the distinguishable features on fracture surfaces of brittle materials.…”

“…The model was found to accurately describe the distinguishable features on fracture surfaces of brittle materials. In the present work, we adapt the model proposed by Dugnani and Zednik (2013) in order to account for the non-linear stress profile of tempered glasses.…”