Conclusions
The cold forming of stainless steel sections induces cold work in
the member, which can enhance the strength but reduce the ductility
of the material. In the nonlinear FE analysis of the structural
behaviour of cold-formed stainless steel members, the stress–strain
relationship of the material in corners (i.e., corner materials) would
be required to produce accurate numerical predictions. This paper
has been concerned with the accurate prediction of the enhanced
strength, reduced ductility and stress–strain behaviour of the corner
material in cold-formed stainless steel sections by presenting an
advanced numerical approach for the simulation of corner coupon
tests. This advanced numerical approach has been implemented
using the FE package ABAQUS [29].
In the present paper, a modified weighted-average method has
been first presented to predict the post-ultimate stress–strain
behaviour of virgin stainless steel sheets up to the fracture strain,
in which the effect of material anisotropy is taken into account. By
incorporating this modified weighted-average method, the
advanced numerical approach has been next presented for pre-
dicting the enhanced stress–strain behaviour and reduced ducti-
lity of corner materials in cold-formed stainless steel sections. In
this approach, the effect of cold work in the corner has been taken
into account by means of a FE simulation of the cold forming of
corners, with the resulting residual stresses and equivalent plastic
strains specified as the initial state in a subsequent FE simulation
of corner coupon tests. Tests of corner materials cut from press-
braked stainless steel sections have been performed and test
results have also been presented in the paper. Numerical predic-
tions from the proposed approach have been shown to agree
closely with test results, demonstrating the accuracy of the
approach.
It is worth noting that lower bound solutions of the corner
ductility and formability of cold-formed stainless steel sections
can be found using the power-law extrapolation (i.e., the weight
constant w¼0) (see Eqs. (4) and (18)) for the post-ultimate stress–
strain behaviour of virgin sheets in the advanced numerical
approach. These lower bound solutions can be deployed in future
research to advance ductility requirements to avoid corner crack-
ing and permit adequate structural performance. It is also impor-
tant to note that the modified weighted-average method and the
general principles of the advanced numerical approach are applic-
able to various cold-worked materials produced from all types of
sheet metals and different cold-forming processes for the assess-
ment of their altered mechanical behaviour and its effect on the
structural performance.