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When
a material is loaded in compression it may buckle when a critical load
is applied. If loading is performed at constant strain-rate, this initial
buckling will be elastic and will be recoverable when the applied compressive
stress is reduced. If loading is continued under these conditions, the
buckled material may deform enough to cause local plastic deformation to
occur. This deformation is permanent and cannot be recovered when the load
is removed.
The
photograph shows a thin wall carbon-steel tube that has been buckled in
compression. The tube has a square section, and the plastic deformation
is self-constraining. Initially, the material deformed elastically. Upon
reaching the buckling threshold, it bowed out and plastic deformation was
initiated at the region of maximum curvature. This "plastic hinge" can
be folded at a lower applied stress than that needed to initiate the buckle.
When the material has closed on itself, a second hinge is generated as
the next tube section starts to buckle and plastically deform. This process
is repeated until the deformation is discontinued. |
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