ABSTRACT
The reports about loading rate effects on hardness of glass and ceramics are contradictory [1-5]. Microhardness of glass increased [2], decreased [3, 4], or remained independent of loading rate [5], while the nanohardness was slightly reduced [6], remained load independent [7-9], or was load dependent [10, 11]. The hardness of glass was slightly reduced [4, 12, 13], while the hardnesses of ceramics [14-16] were either enhanced with strain and loading rate variation or remained insensitive [17] to it. Recently, significant effects of loading rate on hardness of glass (see Chapters 10-12) [18-21], alumina (see Chapters 16-18) [22, 23], and natural biocomposites like human tooth (see Chapter 43) [24, 25] were reported by us. In each of these materials, there was an increase in the nanohardness of the material with the loading rates (see Chapters 10-12, 16-18, 43). Thus, some generic mechanism might have played a pivotal role in the enhancement of the nanohardness.
