Mechanical Properties

Note on Stress:

Stress is defined as the perpendicular force per unit area applied to an object, in a way that compresses (compressive stress) or stretches (tensile stress) the object. Strength is the ability of glass to withstand these stresses. Non-strengthened glass materials have relatively low tensile strength yet high compressive strength. Therefore, most glass breakage is due to tensile stress failure.

Young's Modulus or Modulus of Elasticity; the amount of stress required to produce a unit change in length (strain). Expressed in pounds per square inch (psi) or MegaPascals (Mpa).

Poisson's Ratio - The ratio of the transverse contraction of a bar of glass to the elongation per unit length. Most glasses have a Poisson's ratio of around 0.22.

Modulus of Rupture - The Modulus of Rupture (MOR)strength of glass is determined by tests conducted in accordance with ASTM C 158. This test measures the bending (flexural) strength of glass. Expressed in psi or Mpa.

Shear Modulus - The amount of force that may be withstood by applying the force such that the glass is sheared or twisted.

Bulk Modulus - The inverse of the compressibility of the material, if the material does not exhibit any time dependent response.

Knoop Hardness - A measure of hardness employing a diamond pyramid indenter. The measure of hardness is known as the Knoop hardness number (KHN).

Density - The mass value per unit of volume, such as grams per cubic centimeter (g/cm3).

Specific Gravity - The ratio of the density of the glass to the density of water, given as a fraction.