Indentation methods for evaluating fracture toughness in glass materials: A review

Abstract

Assessing the fracture toughness (K_Ic) of glass remains a significant area of interest in materials science research worldwide. The Single Edge Pre-cracked Beam (SEPB) method is widely regarded as the international standard for measuring fracture toughness in glass and other brittle substances. In contrast, the indentation fracture test (IFT), though based on the theoretical principles of Griffith-Irwin fracture mechanics, continues to generate debate regarding its practical validity and consistency. This review provides a comprehensive overview of the current status and research progress in the application of IFT for glass. A comprehensive analysis of the primary factors influencing IFT measurement accuracy is presented. Comparisons are made with standardized methods such as SEPB and CNB to objectively evaluate the effectiveness and limitations of IFT. The empirical constant ξ exhibits variability influenced by the geometry of the indenter, the resulting crack pattern, and the structural characteristics of the glass. The content and field strength of network modifiers, as well as the relative proportions of bridging and non-bridging oxygens within the glass network structure, play a critical role in governing crack propagation behavior. Moreover, the instrumental resolution and environmental parameters have been shown to significantly affect the accuracy of ${\text{K}}_{\text{Ic}}^{\text{IFT}}$ measurements. Compared with the cracking methods, the densification-induced residual stress field during indentation results in a non-uniform stress distribution within the material. This systematic deviation contributes to discrepancies between the measured ${\text{K}}_{\text{Ic}}^{\text{IFT}}$ value and the true value. This review not only systematically consolidates the current understanding of IFT in glass but also offers critical insights for standardization of the method in future engineering applications.