Necking

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

Numerical investigation of the possibility to determine the primary particle size of fractal aggregates by measuring light depolarization

Abstract: In this paper, depolarization of light ρ = I vh / I vv by fractal aggregates of nanoparticles is considered as a possible way to infer the primary particles radius Rp. A numerical study makes it possible to evaluate the impact of optical and morphological parameters of fractal aggregates (number and size of primary spheres, fractal dimension, overlapping and necking effects) on depolarization ratio and a model is proposed. It appears that for large aggregates, an asymptotic behavior of the depolarization ratio as a function of qR p ( q = 4 π / λ × sin ( θ / 2 ) ) is established promoting the experimental measurement of R p . Nevertheless, there is evidence that particle anisotropy, optical index, primary sphere overlapping and necking effects strongly impact the depolarization ratio. By taking into account all these parameters, a good correspondence is found between experimental and numerical results.

On the mechanics of localized necking in anisotropic sheet metals

Abstract: The ductility of sheet metals formed by cold rolling is often assessed by tension tests on long rectangular strips which are cut from a sheet at various angles to the direction of rolling. A strip typically deforms homogeneously to begin with, but eventually fails at a site where a narrow neck develops along a line that crosses the gauge section obliquely from side to side. The degree of obliquity depends on the material as well as on the cutting angle; so also does the stage of deformation at which a neck first appears. It has long been evident that material orthotropy and progressive hardening are crucial factors, but a theoretical analysis of the phenomenon that takes due account of both of these is apparently still lacking. Their joint influence is investigated here on the basis of the classical rigid/plastic constitutive model in its original form. Some pragmatic notions which were added later are excluded as being too simplistic and unnecessarily restrictive. The present analysis has been deliberately freed from ad hoc empiricism of any kind with a view to more realistic modeling in the future. Other than basic analytic requirements, there are no theoretical limitations on the path dependences of orthotropic parameters and the rate of strain hardening, nor on the evolving geometries of subsequent yield surfaces. It appears to the writer that, with well planned experiments and improved instrumentation, strip tests could be much more effective as a means to investigate orthotropic behaviour in metals.

Coexistent Fluid-Phase Equilibria in Biomembranes with Bending Elasticity

Abstract: The theory of fluid surfaces with elastic resistance to bending is applied to coexistent phase equilibria in biomembranes composed of lipid bilayers. A simplified version of the model is used to simulate the necking and budding of closed vesicles.

Tensile testing of ultra fine grained metals

Abstract: A simple model of neck evolution during tensile testing is suggested. Approximate true stress–true strain diagrams are calculated and analyzed for fine grained and ultra fine grained aluminum alloy Al0.5%Cu. In comparison with ordinary load-elongation diagrams, true diagrams reveal many additional details of the material behavior. Deformation/fracture mechanisms at different tensile stages are discussed.

Understanding the extremely low fracture toughness of freestanding gold thin films by in-situ bulge testing in an AFM

Abstract: The fracture toughness of freestanding gold films with thicknesses between 60 nm and 320 nm was determined by bulge testing to be around 2 MPa m1/2. This surprisingly low value confirms the trend also observed for other metals that thin films exhibit only a fraction of the bulk fracture toughness. In order to understand this behavior, the fracture process of freestanding gold films with a crack introduced by focused ion beam (FIB) milling was observed in-situ in an atomic force microscope (AFM). AFM scans of the crack tip region show stable crack growth mainly along grain boundaries. Plastic deformation is localized in a narrow corridor in front of the crack tip. A large plastic zone, as one would typically expect under plane stress, is not observed. Instead, strong local necking is evidenced. We conclude that the spatial confinement of the plastic deformation is the primary reason for the low fracture toughness of metallic thin films.