Necking

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

Plastic deformation and failure mechanisms in nano-scale notched metallic glass specimens under tensile loading

Abstract: In this work, numerical simulations using molecular dynamics and non-local plasticity based finite element analysis are carried out on tensile loading of nano-scale double edge notched metallic glass specimens. The effect of acuteness of notches as well as the metallic glass chemical composition or internal material length scale on the plastic deformation response of the specimens are studied. Both MD and FE simulations, in spite of the fundamental differences in their nature, indicate near-identical deformation features. Results show two distinct transitions in the notch tip deformation behavior as the acuity is increased, first from single shear band dominant plastic flow localization to ligament necking, and then to double shear banding in notches that are very sharp. Specimens with moderately blunt notches and composition showing wider shear bands or higher material length scale characterizing the interaction stress associated with flow defects display profuse plastic deformation and failure by ligament necking. These results are rationalized from the role of the interaction stress and development of the notch root plastic zones. (C) 2017 Elsevier Ltd. All rights reserved.

Plastic-flow and microstructure evolution during hot deformation of a gamma titanium aluminide alloy

Abstract: The hot workability of a near gamma titanium aluminide alloy, Ti-49.5Al-2.5Nb-1.1Mn, was assessed in both the cast and the wrought conditions through a series of tension tests conducted over a wide range of strain rates (10−4 to 100 s−1) and temperatures (850 °C to 1377 °C). Tensile flow curves for both materials exhibited sharp peaks at low strain levels followed by pronounced necking and flow localization at high strain levels. A phenomenological analysis of the strain rate and temperature dependence of the peak stress data yielded an average value of the strain rate sensitivity equal to 0.21 and an apparent activation energy of ∼411 kJ/mol. At low strain rates, the tensile ductility displayed a maximum at ∼ 1050 °C to 1150 °C, whereas at high strain rates, a sharp transition from a brittle behavior at low temperatures to a ductile behavior at high temperatures was noticed. Dynamic recrystallization of the gamma phase was the major softening mechanism controlling the growth and coalescence of cavities and wedge cracks in specimens deformed at strain rates of 10−4 to 10−2 s−1 and temperatures varying from 950 °C to 1250 °C. The dynamically recrystallized grain size followed a power-law relationship with the Zener-Hollomon parameter. Deformation at temperatures higher than 1270 °C led to the formation of randomly oriented alpha laths within the gamma grains at low strain levels followed by their reorientation and evolution into fibrous structures containing γ + α phases, resulting in excellent ductility even at high strain rates.

High-temperature large strain viscoelastic behavior of polypropylene modeled using an inhomogeneously strained network

Abstract: The effects of microstructural rearrangements during the stretching of semicrystalline polymers and the resultant inhomogeneous strains are modeled by rigid spheres embedded in a polymer network. This results in strain concentrations in the network, which is then caused to yield at realistic overall strains. To simulate the collapse of the original spherulitic morphology, the radii of the spheres decrease at a rate dependent on the shear stress imposed on them by the surrounding network. This results in time-dependent behavior. The resultant large strain viscoelastic model is implemented in a commercial finite element code and used to predict shapes of necking polypropylene sheet specimens at 150°C. Rate dependence of stress and stress relaxation are also predicted, and the model is shown to be generally effective in its predictions of shapes and forces up to large deformations.