<P> Necking, in engineering or materials science, is a mode of tensile deformation where relatively large amounts of strain localize disproportionately in a small region of the material . The resulting prominent decrease in local cross-sectional area provides the basis for the name "neck". Because the local strains in the neck are large, necking is often closely associated with yielding, a form of plastic deformation associated with ductile materials, often metals or polymers . The neck eventually becomes a fracture when enough strain is applied . </P> <P> Necking results from an instability during tensile deformation when a material's cross-sectional area decreases by a greater proportion than the material strain hardens . Considère published the basic criterion for necking in 1885 . Three concepts provide the framework for understanding neck formation . </P>

When does necking occur in terms of the true strain
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