Mechanical properties
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5.1 Young’s modulus E, shear modulus G and poisson ratio µ

Young’s modulus E, shear modulus G and poisson ratio can be calculated with the following formula:



E―Young’s modulus, Pa;

G―Shear modulus, Pa;

V1―Velocity of longitudinal wave;

Vs―Velocity of transverse wave;

μ―Poisson ratio;

ρ―Density of glass.

5.2 Knoop Hardness (HK)

Knoop hardness is measured by the method described in GB/T 7962.18.

For this measurement, a rhombic-shaped diamond indenter with vertically opposite angles of 172°30′ and 130° respectively to the base axes vertically applied to the specimen surface. After keeping indentation loads a certain time, the loads are removed and the length of the longer diagonal dimension of the resulting indentation is measured. Knoop hardness is calculated using the following formula:


F―load, N;

l―length of longer diagonal line, mm;

HK―Knoop hardness, Pa.

5.3 Relative Abrasion Hardness (FA)

Abrasion hardness FA means, under the same condition, the ratio of the volume losses of tested sample (V) and that of the standard sample H-K9L (V0) multiplying 100. The abrasion hardness can be calculated by the following formula:



W0—the mass loss of the standard sample (H-K9L);

W—the mass loss of the tested sample;

ρ0—the density of the standard sample (H-K9L), units in g/cm3;

ρ—the density of the tested sample, units in g/cm3.

5.4 Density (ρ)

The density refers to the mass of per unit volume of optical glass at 20℃. The density of optical glass is in units of g/cm3 and is measured according to the method described in GB/T 7962.20.

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