Necking

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

High‐Temperature‐Creep Mechanism of TiNi

Abstract: Polycrystalline specimens of the intermetallic compound TiNi were tested in tension in the temperature range 700°–1000°C. The specimens were observed to deform uniformly over the gage length until the very end of deformation, when it failed by necking. It was noted that the steady‐state flow stress was independent of the strain and was a function only of the temperature and strain rate. The shear strain rate γ was given by γ∝τn where n=3.0±0.2, r was the shear stress, and n was independent of temperature. The apparent activation energy for creep was found to be 60.0±3.0 kcal/mole and was independent of stress. The result strongly suggests that a viscous creep process, as first formulated by Weertman, is probably the rate‐controlling mechanism for this compound in the stress and temperature range investigated.

Onset of necking in electro-magnetically formed rings

Abstract: The electromagnetic forming (EMF) process is an attractive manufacturing technique, which uses electromagnetic (Lorentz) body forces to fabricate metallic parts. One of the many advantages of EMF is the considerable ductility increase observed in several metals, with aluminum featuring prominently among them. The quantitative explanation of this phenomenon is the primary motivation of this work. To study the ductility increase due to EMF, an aluminum ring is placed outside a fixed coil, which is connected to a capacitor. Upon the capacitor's discharge, the time varying current in the coil induces a larger current in the ring specimen and the resulting Lorentz forces make it expand. The coupled coil–ring electromagnetic and thermomechanical problem is solved, using an experimentally obtained constitutive model for a particular aluminum alloy. Our results show that for realistic imperfections, the EMF ring starts necking at strains about six times larger than its static counterpart, as observed experimentally. This study establishes the importance of solving the fully coupled electromagnetic and thermomechanical problem and provides insight on how different constitutive parameters influence ductility in an EMF process.

Non-isothermal viscoelastic numerical model of the cast-film process

Abstract: The cast-film process is widely used to produce synthetic (polymer) film for a large range of applications. Two geometrical defects contribute to decrease efficiency of this process: the width reduction (necking defect) and the inhomogeneous decrease of the thickness distribution (edge bead defect). In this paper, a numerical simulation of the process is performed to predict these defects. A membrane approximation is used to reduce the equations to a 2D model. The polymer flow is non-isothermal (heat transfer coefficient is discussed) and a viscoelastic constitutive equation is accounted for.

Ductility and formability of three high-Mn TWIP steels in quasi-static and high-speed tensile and Erichsen tests

Abstract: The ductility and formability properties of three high-Mn TWIP steels were investigated under quasi-static and high-speed deformation conditions. The ductility was evaluated from conventional and Hopkinson split-bar tensile tests at 1250 s−1 and the stretch formability was evaluated using Erichsen tests made with a special high-speed electro-hydraulic forming machine at about 1000 s−1. The data were related to microstructural features revealed using electron backscatter diffraction and X-ray diffraction. Furthermore, the stacking fault energy (SFE) was estimated using a thermodynamic approach. It was found that the 0.6C-22Mn and 0.2C-21Mn-0.23N steels (compositions in wt%) with SFEs of 23–24 mJ/m2 exhibited good elongation and a large Erichsen index at both low and high strain rates. These were attributed to intensive mechanical twinning though partly replaced by dislocation slip in deformation bands in the high-speed tests. However, it was noticed that the high-speed stretching failure of these TWIP steels occurred in the uniform elongation range without diffuse necking. In the austenitic - ferritic 21Mn-3Al-3Si steel strain-induced martensite was formed, but the ferrite phase seemed to impair formability.