Abstract
A new biaxial tension testing machine with flat specimens has been designed and constructed to investigate the plastic behavior of metal under biaxial tension. The capacity of this machine is 5 tons and the stroke is 100mm. The specimen is made in cross-shape. Its dimensions were so determined as to make the region of homogeneous plastic deformation in the middle of the specimen as large as possible. The determination of the stress in the specimen was found possible by the use of the equivalent sectional area.
By assuming the yield point as the stress of a permanent set of 200×10-6, an initial and three subsequent yield surfaces were experimentally determined with eleven brass specimens. The following results were obtained from this experiment.
The initial yielding follows Mises condition. After prestraining in the principal stress direction:
(1) The subsequent yield surfaces are translated in the direction of prestrain.
(2) The subsequent yield surfaces do not expand isotropically in any direction.
(3) The expansion of subsequent yield surfaces was found quite small.
