Necking

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

Necking mechanism and its elimination in uniaxially drawn films of poly(ethylene naphthalate) (PEN)/polyetherimide (PEI) blends

Abstract: The influence of blend composition on the deformation behavior of cast amorphous PEN/PEI blends were investigated above their respected glass transition temperatures. PEN inherently shows a sharp necking phenomenon when stretched at temperatures as high as 20°C above its glass transition temperature. This was attributed to highly localized rapid alignment of naphthalene planes parallel to the surface of the films. The addition of PEI was observed to reduce this necking behavior. The neck formation completely disappears when the PEI fraction exceeds 10% in the blend. X-ray studies indicate that the increase of PEI hinders the rapid alignment of naphthalene planes parallel to the surface of the films. The presence of PEI chains in the blend was found to increase the overall friction between the polymer chains in the system and this was found to prevent the formation of highly localized necks. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2059–2074, 1997

Forming and fracture limits of austenitic stainless steel sheets

Abstract: The limit of straining of austenitic stainless steels in ordinary stretch forming, when both of the principal strains are positive, is usually not set by localized necking, but instead by inclined shearing fracture in the through thickness direction It appears that the forming limits of austenitic stainless steels may be predicted fairly well by using the classical localized and diffuse necking criteria developed by Hill The strain path-dependence may be accounted for by integrating the effective strain along the strain path The modified Rice–Tracey fracture criterion seems to give a reasonable estimate for fracture limit strains The Cockcroft, Latham and Oh criterion, however, underestimates the fracture limit Necking limit strains are strongly dependent on the strain path The fracture limit strains calculated using the modified Rice–Tracey criterion, however, did not depend as much on the strain path as the necking limit strains

Grain-orientation-dependent of γ–ε–α′ transformation and twinning in a super-high-strength, high ductility austenitic Mn-steel

Abstract: A newly developed, austenitic lightweight steel, containing a low-density element, Al, exhibits tensile elongation up to 50% as well as high ultimate-tensile stress (tensile fracture at 1800 MPa) without necking behavior. Electron backscatter diffraction analysis is carried out to investigate the orientation dependence of the martensitic transformation in tensile testing to 30% strain at 323 K (25 °C). A pronounced γ→e→α′ transformation is observed in and ∥TD (TD: tensile direction) γ-grains. The α′-transformation textures is analyzed. Large misorientation spreads is seen in the ∥TD γ-grains. Interestingly, twin-assisted martensitic transformation is detected in the ∥TD followed by the twin boundary directly moving to a γ/α′ phase boundary. These phenomena are related to a change of Schmid factor for different orientations of grains.

Prediction of formability for non-linear deformation history using generalized forming limit concept (GFLC)

Abstract: The prediction of formability is one of the most important tasks in sheet metal process simulation. The common criterion in industrial applications is the Forming Limit Curve (FLC). The big advantage of FLCs is the easy interpretation of simulation or measurement data in combination with an ISO standard for the experimental determination. However, the conventional FLCs are limited to almost linear and unbroken strain paths, i.e. deformation histories with non-linear strain increments often lead to big differences in comparison to the prediction of the FLC. In this paper a phenomenological approach, the so-called Generalized Forming Limit Concept (GFLC), is introduced to predict the localized necking on arbitrary deformation history with unlimited number of non-linear strain increments. The GFLC consists of the conventional FLC and an acceptable number of experiments with bi-linear deformation history. With the idea of the new defined “Principle of Equivalent Pre-Forming” every deformation state built up of two linear strain increments can be transformed to a pure linear strain path with the same used formability of the material. In advance this procedure can be repeated as often as necessary. Therefore, it allows a robust and cost effective analysis of beginning instability in Finite Element Analysis (FEA) for arbitrary deformation histories. In addition, the GFLC is fully downwards compatible to the established FLC for pure linear strain paths.

Simulation of ductile crack propagation in dual-phase steel

Abstract: The modified Mohr–Coulomb and the extended Cockcroft–Latham fracture criteria are used in explicit finite-element (FE) simulations of ductile crack propagation in a dual-phase steel sheet. The sheet is discretized using tri-linear solid elements and the element erosion technique is used to model the crack propagation. The numerical results are compared to quasi-static experiments conducted with five types of specimens (uniaxial tension, plane-strain tension, in-plane shear, 45° and 90° modified Arcan) made from a 2 mm thick sheet of the dual-phase steel Docol 600DL. The rate-dependent J2 flow theory with isotropic hardening was used in the simulations. The predicted crack paths and the force–displacement curves were quite similar in the simulations with the different fracture criteria. Except for the 45° modified Arcan test, the predicted crack paths were in good agreement with the experimental findings. The effect of using a high-exponent yield function in the prediction of the crack path was also investigated, and it was found that this improved the crack path prediction for the 45° modified Arcan test. In simulations carried out on FE models with a denser spatial discretization, the prediction of localized necking and crack propagation was in better accordance with the experimental observations. In four out of five specimen geometries, a through-thickness shear fracture was observed in the experiments. By introducing strain softening in the material model and applying a dense spatial discretization, the slant fracture mode was captured in the numerical models. This did not give a significant change in the global behaviour as represented by the force–displacement curves.