Deformation and fracture of notched polycarbonate specimens

1.	Polycarbonate specimens enable direct observation of the stress-strain pattern during the loading process.
2.	It has been shown that under plane strain and plane stress conditions the crack starts at the boundary of the elastic-plastic deformation zone at the moment when the normal stress component reaches the critical value.
3.	Under plane strain conditions the value cr is determined by the yield point and the radius of the notch n. Under plane stress conditions the strip of plastic deformation functions, as a stress concentrator. Fracture occurs when the normal stress component at the boundary reaches the critical value.
4.	During the intervals when the specimen is not loaded the plastically deformed zones act as concentrators of residual stress. When load is again applied there is interaction between the residual stresses and the externally induced stresses.