Necking

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

On the tensile behaviour of oriented polyethylene

Abstract: Tensile tests of oriented, high-density, polyethylene films were carried out in order to assess how far the intrinsic molecular and textural features of the samples affected their mechanical behaviour, and to see whether this behaviour bore any resemblance to that of metals. Brittle fracture, ductile fracture or necking followed by drawing occurred, depending on the pretreatment used to orient the material, the angle between the tensile axis and the c axis, and the speed of testing. The feature of the crystalline texture (common to all the films) which was important in determining the geometry of deformation was the alignment of the c axis; the additional orientations present in some of the films did not significantly affect the deformation geometry. The results suggested that ductile deformation approximated to slip in the direction of the c axis, while brittle fracture was observed to occur on planes parallel to the c axis. There were some noticeable differences in behaviour between those films which had received a pre-anneal and those which had not; these differences appeared not to be due to differences in the crystalline texture. Several striking similarities to the mechanical behaviour of hexagonal single crystals were observed.

Tensile deformation of electroplated copper nanopillars

Abstract: The results are presented of uniaxial tensile testing of single crystalline electroplated copper nanopillars with diameters between 75 nm and 165 nm fabricated without the use of a focused ion beam (FIB). The experiments were performed in an in situ nanomechanical instrument, SEMentor, and reveal that the pillars’ ultimate tensile strengths follow a similar power law dependence on diameter as reported for microcompression studies on fcc metals fabricated with and without FIB. Further, these pillars are characterized by limited or non-existent initial homogeneous deformation, immediately followed by necking in the top portion of the pillar. The particular deformation attributes are discussed in the context of hardening by dislocation starvation. Site-specific transmission electron microscopy microstructural analysis of as-fabricated nanopillars indicates the presence of scarce twin boundaries in some specimens. We comment on the potential for mechanical effects due to the presence of twins.

Material aspects of dynamic neck retardation

Abstract: Neck retardation in stretching of ductile materials is promoted by strain hardening, strain-rate hardening and inertia. Retardation is usually beneficial because necking is often the precursor to ductile failure. The interaction of material behavior and inertia in necking retardation is complicated, in part, because necking is highly nonlinear but also because the mathematical character of the response changes in a fundamental way from rate-independent necking to rate-dependent necking, whether due to material constitutive behavior or to inertia. For rate-dependent behavior, neck development requires the introduction of an imperfection, and the rate of neck growth in the early stages is closely tied to the imperfection amplitude. When inertia is important, multiple necks form. In contrast, for rate-independent materials deformed quasi-statically, single necks are preferred and they can emerge in an imperfection-free specimen as a bifurcation at a critical strain. In this paper, the interaction of material properties and inertia in determining neck retardation is unraveled using a variety of analysis methods for thin sheets and plates undergoing plane strain extension. Dimensionless parameters are identified, as are the regimes in which they play an important role.