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Necking

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


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TL;DR: In this paper, a constitutive model is proposed to describe the transformation plasticity accompanying strain-induced martensitic transformation in nonthermoelastic alloys, and a selfconsistent method is then used for predicting the resultant stress-strain behavior.
Abstract: We propose a constitutive model which describes the transformation plasticity accompanying strain-induced martensitic transformation in nonthermoelastic alloys. The model consists of two parts: a transformation kinetics law describing the evolution of the volume fraction of martensite and a constitutive law defining the flow strength of the evolving two-phase composite. The Olson-Cohen model for martensite volume fraction evolution is recast in a generalized rate form so that the extent of martensite nucleation is not only a function of plastic strain and temperature, but also of the stress state. A selfconsistent method is then used for predicting the resultant stress-strain behavior. The model describes both the hardening influence of the transformation product, and the softening influence of the transformation itself, as represented by a spontaneous transformation strain. The model is then implemented in a finite element program suitable for analysis of boundary value problems. Model predictions are compared with existing experimental data for austenitic steels. We present results from a few simple analyses, including tensile necking, illustrating the critical importance of stress state sensitivity in the evolution model.

466 citations

Journal ArticleDOI
TL;DR: In this paper, a comprehensive study on a series of polyethylene (PE) samples encompassing a large range of crystallinities was carried out using a video-controlled tensile testing machine.
Abstract: When polyethylene (PE) is deformed to large strains, the stress originates from both the viscous forces associated with the plastic deformation of the crystallites by slip and fragmentation processes and the entropic elastic forces arising from the stretching of the entangled amorphous regions. Relative weights of the different processes change with the crystallinity. The dependencies were analyzed in a comprehensive study on a series of samples encompassing a large range of crystallinities: PE, low-density PE (LDPE), and ethylene−vinylacetate copolymers. The comparison was based on measured true stress−strain curves for constant strain rates. For the samples with higher crystallinity, which show a necking, this was achieved by employing a video-controlled tensile testing machine. Recovery properties of the sample were studied in step-cycle runs, where the load was applied stepwise and interrupted after each step by an unloading−reloading loop. Simultaneous with the mechanical testing, the related textur...

455 citations

Journal ArticleDOI
TL;DR: In this paper, an unconditionally stable algorithm for the numerical integration of elastoplastic pressure-dependent constitutive relations is analyzed in detail, and the application of the method to plane stress problems, in which the out-of-plane strain component is not defined kinematically, is discussed.
Abstract: An unconditionally stable algorithm for the numerical integration of elastoplastic pressure-dependent constitutive relations is analysed in detail in this paper. The application of the method to plane stress problems, in which the out-of-plane strain component is not defined kinematically, is discussed. The tangent moduli resulting from this integration algorithm are obtained by consistent linearization of the elastoplastic constitutive equations. The algorithm is applied to Gurson's constitutive model, some one-dimensional problems are solved, and comparisons with exact solutions are made. The paper closes with a numerical study of the necking of an axi-symmetric specimen using Gurson's plasticity model to describe the constitutive behaviour of the material.

429 citations

Journal ArticleDOI
TL;DR: In this article, the deformation behavior of ultrafine-grained (UFG) Ti samples has been systematically characterized, including strain hardening, strain rate dependence of flow stress, deformation/failure mode, and tensile necking instability.
Abstract: Ultrafine-grained (UFG) Ti samples have been prepared using equal channel angular pressing followed by cold rolling and annealing. The deformation behavior of these materials, including strain hardening, strain rate dependence of flow stress, deformation/failure mode, and tensile necking instability, have been systematically characterized. The findings are compared with those for conventional coarse-grained Ti and used to explain the limited tensile ductility observed so far for UFG or nanocrystalline metals.

414 citations

Journal ArticleDOI
TL;DR: Transmission electron microscopy and atomistic simulations demonstrate that shear banding instability no longer afflicts the 5- to 10-nm-thick nanolaminate glassy layers during tensile deformation, which also act as high-capacity sinks for dislocations, enabling absorption of free volume and free energy transported by the dislocation.
Abstract: It is known that the room-temperature plastic deformation of bulk metallic glasses is compromised by strain softening and shear localization, resulting in near-zero tensile ductility. The incorporation of metallic glasses into engineering materials, therefore, is often accompanied by complete brittleness or an apparent loss of useful tensile ductility. Here we report the observation of an exceptional tensile ductility in crystalline copper/copper–zirconium glass nanolaminates. These nanocrystalline–amorphous nanolaminates exhibit a high flow stress of 1.09 ± 0.02 GPa, a nearly elastic-perfectly plastic behavior without necking, and a tensile elongation to failure of 13.8 ± 1.7%, which is six to eight times higher than that typically observed in conventional crystalline–crystalline nanolaminates (<2%) and most other nanocrystalline materials. Transmission electron microscopy and atomistic simulations demonstrate that shear banding instability no longer afflicts the 5- to 10-nm-thick nanolaminate glassy layers during tensile deformation, which also act as high-capacity sinks for dislocations, enabling absorption of free volume and free energy transported by the dislocations; the amorphous–crystal interfaces exhibit unique inelastic shear (slip) transfer characteristics, fundamentally different from those of grain boundaries. Nanoscale metallic glass layers therefore may offer great benefits in engineering the plasticity of crystalline materials and opening new avenues for improving their strength and ductility.

402 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023174
2022351
2021241
2020249
2019213
2018238