Factors affecting plastic instability and sheet formability
Factors affecting plastic instability and sheet formability The strong influence of geometry and materials properties on plastic instability and sheet formability is illustrated with several experimental observations. Geometry (shape) of the specimen or work piece and the evolution of shape with deformation is of great importance. Experiments on sheet and thin-walled tubes have demonstrated convincingly that sheets stretched over a punch are more stable than sheets stretched in-plane; which, in turn, are more stable than expanded thin-walled tubes. All can be explained by the specific interaction of specimen shape with loads and deformations. The materials parameters of greatest importance (Hecker, 1978a) are strain hardening, strain-rate sensitivity, and plastic anisotropy. Several experiments are cited that demonstrate the importance of stress state, large strains, and path changes on the strain-hardening response and on subsequent stability.
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