Abstract
Residual stress in injection molded specimens having a round or rectangular hole was investigated by photoelastic analysis. Though molten resin flowed as the resin surrounded either side of the hole, and met at the opposite side of the gate, one of principal stress trajectories derived from isoclinic patterns coincided roughly with the shapes of the flowing resin front. Stress in the specimens was concentrated about the hole, and the greatest concentration developed at the side of the hole near the gate. The isochromatic fringe order curves about the round hole were smoother than those about the rectangular hole, and the stress concentration in the specimens having the round hole was less that in the specimens having a rectangular hole. In specimens having rectangular holes of the same size and the same shape, the molten resin readily flowed around the rectangular hole with it's short side pointing to the gate in comparison with that with it's long side pointing to the gate. Though both specimens had a maximum principal stress of 207.0 kgf/cm2, the extent of this stress was small in the specimen having the rectangular hole with it's short side pointing to the gate.
