Page 132 - Chalcogenide Glasses for Infrared Optics

Characterization of Glass Pr operties 109

that is observed, and the millimeter length is measured using the
scale in the microscope of the instrument. Several measurements
may be made and averaged. The Knoop hardness (KH) is calculated
from the standard formula.
P
KH = 14.23 × 10 ×
3
L 2
where P = load in g
L = indention length in mm

4.3.2 Young’s Modulus, Shear Modulus, and Poisson’s Ratio
These data provide information to mechanical engineers concerned
with the physical strength of each component in their systems. AMI
uses simple sound velocity measurements to measure Young’s Mod-
ulus E, shear modulus G, and Poisson’s ratio ν. Figure 4.14 shows a
photograph of the simple device AMI used to measure sound in glass,
the Panametrics 25-hp Plus Ultrasonic Thickness Gauge. Also in the photo-
graph, right next to the gauge, is the Thermal Comparator, the instru-
ment used by AMI to measure thermal conductivity of the glasses to
be discussed in a later section. The thickness gauge instrument is
equipped with a sensing head that uses transducers suited for longi-
tudinal sound wave measurements or a transducer suitable for shear
sound wave measurements. The velocity of each wave in the glass is
directly measured, and along with the density ρ of the glass, Young’s

FIGURE 4.14 The Panametric 25-hp Plus Ultrasonic Thickness Gauge and the
Thermal Comparator.