Necking

About: Necking is a research topic. Over the lifetime, 5280 publications have been published within this topic receiving 113945 citations.

Tensile ductility of superplastic ceramics and metallic alloys

Abstract: Superplastic ceramics and metallic alloys exhibit different trends in tensile ductility in the range where the strain-rate-sensitivity exponent, m, is high (m⩾0.5). The tensile ductility of superplastic metallic alloys (e.g. fine-grained zinc, aluminium, nickel and titanium alloys) is primarily a function of the strain-rate-sensitivity exponent. In contrast, the tensile ductility of superplastic ceramic materials (e.g. zirconia, alumina, zirconia-alumina composites and iron carbide) is not only a function of the strain-rate-sensitivity exponent, but also a function of the parameter ⋗e exp (Qc/RT) where ⋗e is the steady-state strain rate and Qc is the activation energy for superplastic flow. Superplastic ceramic materials exhibit a large decrease in tensile elongation with an increase in ⋗e exp (Qc/RT). This trend in tensile elongation is explained based on a “fracture-mechanics” model. The model predicts that tensile ductility increases with a decrease in flow stress, a decrease in grain size and an increase in the parameter (2γs−γgb), where γs is the surface energy and γgb is the grain boundary energy. The difference in the tensile ductility behavior of superplastic ceramics and metallic alloys can be related to their different failure mechanisms. Superplastic ceramics deform without necking and fail by intergranular cracks that propagate perpendicular to the applied tensile axis. In contrast, superplastic metallic alloys commonly fail by intergranular and transgranular (shearing) mechanisms with associated void formation in the neck region.

Forming limit diagrams by including the M–K model in finite element simulation considering the effect of bending:

Abstract: Forming limit diagram is often used as a criterion to predict necking initiation in sheet metal forming processes. In this study, the forming limit diagram was obtained through the inclusion of the...

High strain rate superplasticity of submicrometer grained 5083 Al alloy containing scandium fabricated by severe plastic deformation

Abstract: High strain rate superplasticity (HSRS) was obtained in a commercial 5083 Al alloy by introducing a ultrafine grained structure of 0.3 mm through severe plastic deformation and by adding a dilute amount of scandium (Sc) as a microstructure stabilizer. Tensile tests were carried out on the as-processed sample at temperatures of 623/823 K and initial strain rates of 1/10 3 /1/10 0 s 1 . The maximum elongation to failure of 740% was obtained at 773 K and 1/10 2 s 1 . HSRS of the alloy was attributed to the combined effects of dynamic recrystallization and preservation of fine recrystallized grains by the presence of Sc. The mechanical behavior of the alloy at 773 K was characterized by a sigmoidal behavior in a plot of stress vs strain rate in the double logarithmic scale. The origin of the sigmoidal behavior was discussed in terms of microstructural evolution during superplastic deformation. An examination of the fractured samples revealed that failure occurred in a brittle manner related to cavitation rather than necking. Cavity stringers were formed parallel to the tensile axis by interlinkage of jagged-shaped isolated cavities along grain boundaries aligned to the tensile axis. # 2002 Elsevier Science B.V. All rights reserved.