Stresses in glasses Flashcards
What happens to a glass bottle formed in a steel water-cooled mold? The interior and exterior?
~ exterior: cools quickly to liquid like LOW density, puts TENSILE stress on interior
~ interior: insulated by exterior, cools slowly and condenses to HIGH density, puts COMPRESSIVE stress on exterior
How do we prevent these bottles from spontaneously bursting on store shelves?
~ annealing: reheating bottle to annealing point and holding for short time
~ enough thermal energy is provided for RELAXATION of atomic strains, but viscosity is high enough so part doesn’t slump
What are polariscopes used for? How do they work?
~ checking for residual stresses in a glass part
~ unstrained glass = isotropic, appears dark
~ strained glass = birefringent, appear as colors