Abstract
Residual strain in injection molded specimens of linear polymer (polystyrene) is photoelastically analyzed.
In the samples, isochromatic patterns of high orders are observed. The retardation observed seems to be based upon two types of residual strains: (1) frozen molecular orientation caused by the flow of molten linear polymer in molding process, and (2) that by thermal stress as the result of quenching in dies. This is ascertained by the fact that isochromatic patterns are scarecely changed when sliced at an ordinary temperature, and that a remarkable decreasing of isochromatic fringe order occurs accompanying shrinkage and deformation of the samples when annealed at temperatures higher than the secondary transition point.
Principal stress trajectories derived from isoclinic patterns seem to coincide with thedirection of flow in molten linear polymer. Therefore, photoelastic analysis may also be applied to study the state of flow of molten polymer in molding process.
A few results on the relations between the maximum isochromatic fringe orders in molded specimens and molding conditions were obtained.
