On the relation between fracture toughness and crack resistance in oxide glasses

The resistances of glasses to crack initiation and crack growth are both important parameters for evaluating their mechanical performance. However, it is important to distinguish them as they refer to different mechanical phenomena. In this work, we study the difference in resistance to crack initiation and growth by determining the load required to induce indentation cracking (named crack resistance, CR) and the fracture toughness (K_Ic), respectively, for six oxide glasses with a wide range of CR values from as low as 0.05 N to above 100 N. These new data as well as existing literature data suggest that there is no systematic relation between CR and K_Ic, and as such, we conclude that these two terms should not be used interchangeably. We discuss the origin of the lacking relation by considering the competing effects of glass structure, rigidity, and atmospheric humidity on crack initiation and growth.