FEA results mimicking this cylinder compression process are shown in
Fig. 9.7(b). The analysis reveals the well-known fact that a deformation shear cross
forms inside the cylinder when there is friction between the die and the cylinder. The
largest deformations will appear in the shear cross. When the cylinder has been compressed
down to a certain stage, the initial strain-hardening part of the flow curve
has been exceeded for the material in the shear layer. With continued compression,the shear layer will then experience strain-induced softening. Deformations then
will tend to localize in a thin layer, as marked with the broken line in this figure.
Because of strain softening, this layer will then easily become overstrained, and a
shear fracture will form here.
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