“Frozen Stress” Phenomenon in Photo-Elasticity

Tensile tests were carried out at different temperatures and under different stresses on “Marco Resin SB. 26c”, “Fosterite”, and “Bakelite”. Loads were applied through hinged pads acting on inclined faces at the ends. The separate existence of an “instantaneous”† (room temperature) as well as a “delayed” (“frozen”) optical effect was proved for Marco. “Hot delayed” fringe orders (fringe reading at test temperature—no load fringe order at test temperature—corresponding instantaneous fringe order) are distinguished from “residual” fringe orders (fringe order after freezing cycle— fringe order before). Hot delayed and residual fringe orders and strains were found to be proportional to stress at all temperatures tested. Fringe orders and strains showed maximum values at certain temperatures.

An increase in fringe order during cooling under constant stress was observed in Fosterite and Bakelite. Except for this and the opposite sense of instantaneous and delayed fringe orders in Marco and Fosterite, the three materials behaved similarly.