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The prediction of the yielding and flow behaviour of materials under
complex stress systems from tensile test or other easily determined data
has been the aim of engineers for many years. The yield criteria of Tresca
and then Mises for isotropic metals are useful, but the realisation that
anisotropy is the rule rather than the exception, especially in sheet metals
led to the examination of Hill's anisotropic theory by various workers. In
the present paper the stress-strain curves of various sheet metals are
determined in uniaxial and balanced biaxial tension. As far as yielding
behaviour is concerned it is concluded that the theory is reasonably satisfactory
for materials where anisotropy is described with r = 1, with certain
anomalies for materials with r< 1. As far as flow behaviour is concerned,
the theory only applies for materials for r> 1. Crossing of the uniaxial
and biaxial curves is observed for certain metals at low strains and this
is not predicted by the theory. More work is necessary on low-r materials
to resolve these matters. |
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