Fractographic Strength Estimation of Chemically Strengthened Aluminosilicate Glasses

Date: 2022/11/03 - 2022/11/03

Dissertation Title: Fractographic Strength Estimation of Chemically Strengthened Aluminosilicate Glasses

Speaker: Huan Sun, Ph.D. candidate at UM-SJTU Joint Institute

Time: 2022, November 3th from 9:30 to 11:30 a.m. ( Beijing Time)

Location: Room 503, JI Longbin Building


Chemical strengthening is extensively used in both the electronic and aerospace industries. Fractographic analysis of chemically strengthened (CS) glasses can potentially save costs and provide safer products. However, the current, state-of-art fractographic methods to estimate the strength of brittle materials are limited to annealed samples and no standard exists to provide guidelines on how to examine fractured CS components.

This thesis introduces a novel, fractographic method to extend the current fractographic techniques to CS aluminosilicate glass (ASG) plates fractured in flexure due to the presence of relatively large, surface flaws. The scenario of CS ASG plates considered is a representative of practical fracture occurred in glass components with serious surface damage. The proposed method defines new length-scales for CS glasses equivalent to those in annealed materials but accounting for the presence of steep, residual stresses. The approach utilizes dimensional analysis to correlate the flexural strength to newly introduced, fractographic length-scales and apparent fracture toughness. The fractographic technique requires precise knowledge of the residual stress profile to calculate the apparent fracture toughness, in addition to standard visualization tools such as optical microscopes to measure length-scales. Prior to the fractographic analysis, a modified contour method is developed based on a proposed analytical displacement weight function which considers non-homogenous Young’s modulus and Poisson’s ratio, to estimate the residual stress of CS glass plates through the contour on the mating fracture surfaces. The modified contour method was used to precisely characterize the residual stress profiles in the CS ASG plates with three soaking times.

This thesis is motivated by the lack of any reliable fractographic method to quantitatively establish the fracture strength of CS glasses. The proposed fractographic methodology was validated on three sets of CS ASG plates with depth of the compressive layer ranging between 28–54 μm and surface stresses ranging between 980–1140 MPa, and one set of untreated ASG plates. For the CS and untreated glass plates considered, the proposed fractographic technique estimated the fracture strength within (2±11)% of the measured, experimental strength, which is comparable to the accuracy of current fractographic methods used for annealed and untreated glasses.


Huan Sun received her B.S. degree in School of Material Science and Engineering from Huazhong University of Science and Technology, China, in 2017. Now, she is a Ph.D. candidate student at University of Michigan-Shanghai Jiao Tong University Joint Institute, supervised by Professor Roberto Dugnani. Her current research focuses on the fractographic strength analysis in chemically strengthened glasses.