Cracking in Fused Quartz During Nanoindentation

Brittle materials, such as glass, are commonly used today in society in smaller volumes and/or in the form of thin films. There is a need to better understand how these materials fracture due to small-scale contact and impact. Nanoindentation studies with different indenter geometries were performed on fused quartz, which is a common reference brittle material and is used in applications such as consumer electronics and semiconductors. Three sided pyramidal indenters with centerline-to-face angles of 35.3° (cube corner), 45°, 55°, 65.3° (Berkovich), and 75° were utilized and maximum peak loads (1, 3, 5, 10, 40, 100, and 500 mN) were reached during the nanoindentation experiments to examine the cracking threshold loads and crack lengths. Surface cracking observations were made using a high resolution scanning electron microscope. The scanning electron microscope is equipped with a focused ion beam that was used to mill through the indentations and expose the cracking features below the indentation impression. The crack formation and evolution of the subsurface cracking are presented and compared to other observations made by other researchers. Finite element analysis was used as a tool to establish which stresses play a role in some of the cracking and deformation features of the indentations. Though the fracture toughness was not calculated in this work, the constants from two equations that relate the indentation crack lengths to the fracture toughness were evaluated and compared to other documented constants. This work provides insight into how various cracks initiate and propagate during small-scale contact