New strain standards for glass-ware stress photoelastic evaluation

Strain viewers are used for residual strain evaluation and assessment of glassware. Most viewers are the crossed-nicol type photoelastic apparatus with tint plates, in which the tint colour in the field of view changes with the insertion of strained glassware. Strain standards, which give known or predetermined optical path differences, are necessary for qualitative evaluation of residual internal stress in glassware. Two types of new strain standards, namely rotary-plate type and film-array type, are proposed and presented in detail.