抄録
The method of straining grooved tensile specimens suggested by Hill has been applied to the finding of the criterion for necking of polycarbonate. The specimen is in the form of a strip grooved obliquely on its surface. If such a strip is pulled in tension, deformation will be confined to the grooved regions. The state of stress produced in the zone of deformation is biaxial, owing to the constraint of the surrounding material. It is by the measurement of the maximum load, for a range of groove angles, that the deduction of the criterion for necking of polycarbonate under any state of combined stress is possible.
The results are as follows: The due stress at the maximum load increases appreciably, as the state of stress in the grooved region changes from that of thin-walled tube subjected to internal pressure to that of uniaxial tension of solid bar. In order to examine the anisotropy of polycarbonate plate, the small specimens cut at five different angles with respect to the longitudinal direction were each tested in simple tension. The strip specimens were found approximately isotropic.
In consequence of these investigations, it is concluded that necking of polycarbonate is due to mechanical instability, in so far as the stress of the specimen is in a state of tension between the biaxial and the uniaxial.
