Specialty Optical Fibers Handbook

blunter Vickers pyramid indenter, cracking may occur on unloading and, there-

fore, is driven by the residual stresses developed during the plastic deformation

associated with formation of the permanent impression.

24.2.3 Composition Effects

Table 24.1 lists a number of typical inorganic glasses that may be of use as

light guides or in light-guide devices, together with some of their important

properties. E is the Young’s modulus, K

IC

is the fracture toughness, H

V

is the

Vickers hardness, T

g

is the glass transition temperature, and a is the coefficient

of thermal expansion. Columns five through eight list some strength values and

are described later. As indicated earlier, glasses are often referred to as brittle,

whereas as can be seen here, they can