5.1 Young’s modulus E, shear modulus G and poisson ratio µ
Young’s modulus E, shear modulus G and poisson ratio μ of optical glass can be calculated with the following formula:
Where: E―Young’s modulus, Pa;
G―Shear modulus, Pa;
VL―Velocity of longitudinal wave , m/s;
VT―Velocity of transverse wave, m/s;
μ―Poisson ratio;
ρ―Glass density, g/cm3.
5.2 Knoop Hardness HK
Knoop hardness is measured with micro hardness tester. For this measurement, a pyramid-shaped diamond indenter with vertex-angles 172°30′ and 130°with a rhombic base is applied to the polished specimen surface for 15 seconds, and then remove the loads and the length of the longer diagonal of the resulting indentation is observed with a microscope. Knoop hardness is computed with formula (15):
HK＝1.451•F/d2•••• •••••••••• ••••••••••••••••• •••••••••••••••••（15）
Where: F―Load, N;
d―The length of the longer diagonal of the indentation, mm;
HK―Knoop hardness, 107Pa.
5.3 Abrasion factor FA
Fix a 30×30×10mm glass sample horizontally on the cast iron flat, rotating at 65 rpm. The test piece is located 80mm from the centre of the flat and is under a 9.8N load. Grind continuously with W14# emery grinding fluid for 3 minutes. Test sample weight before and after grinding, and calculate weight loss W. Test weight loss W0 of standard glass H-K9L by the same method. Calculate abrasion factor FA by formula (16):
FA＝V/V0×100＝（W/ρ）/（W0/ρ0）×100•••• •••••••••••••••（16）
Where: W0—The grinding weight loss of the standard glass H-K9L, g ;
W—The grinding weight loss of the test sample, g;
ρ0—The density of the standard glass H-K9L, g/cm3;
ρ—The density of the test sample, g/cm3.
5.4 Density ρ
Density refers to the mass of per unit volume of optical glass at specified temperature. Use the size of buoyancy of object immersing in a medium equaling to medium weight discharged by this object can obtain glass density ρ, that is drainage method.