Necking

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

Breathable and Skin-Mountable Strain Sensor with Tunable Stretchability, Sensitivity, and Linearity via Surface Strain Delocalization for Versatile Skin Activities’ Recognition

Abstract: Metal film/elastomer-based strain sensors usually exhibit small rupture strain (<5%) because of the strain localization and necking effect of the metal film under tension. To achieve both high stretchability and wide linear region is still challenging for metal film-based strain sensors. Here, we propose a low-cost yet effective strategy for fabricating ultrathin, breathable, and skin-mountable strain sensors with high sensitivity (gauge factor from 7.2 to 474.8), high stretchability (up to 140%), and good linearity by regulating the surface strain delocalization in the metal film on elastomer substrate. On the basis of this phenomenon of strain delocalization, the sensitivity and linearity are further enhanced based on a novel diffraction-induced Au film with gradient thickness. Meanwhile, by means of the strain redistribution and Poisson effect, a novel biaxial strain sensor is designed for recognition of complex human motion. On the basis of the enhanced stretchability, linearity, skin-mountable, and breathable properties, the low-cost metal film-based strain sensors can be broadened as disposable wearables for human motion detection, emotional expression recognition, human interaction, and virtual reality.

Influence of microstructure-driven strain localization on the ductile fracture of metallic alloys

Abstract: Most models in the literature that are used to understand and predict ductile failure, ductility or fracture toughness implicitly consider that the plastic response of the material is homogeneous at the level of the microstructure. However, in a number of situations, plasticity is intrinsically localized, because the microstructure is spatially heterogeneous, or because the loading leads to strain localization on the microscale, such as in fatigue loading, or because the dynamics of plastic flow are unstable, such as in Portevin-Le Chatelier instabilities. This paper presents, from analysing various examples, the influence of these strain localization phenomena on the ductile fracture behaviour of metallic alloys. Examples to illustrate these effects will be chosen from, firstly, internal necking between cavities growing to ductile fracture, secondly, damage mechanisms from fatigue persistent slip bands, thirdly, the effect of Portevin-Le Chatelier bands on toughness and, fourthly, damage mechanisms in alloys with precipitate-free zones at grain boundaries.

Strain rate measurement by Electronic Speckle Pattern Interferometry: A new look at the strain localization onset

Abstract: In-plane Electronic Speckle Pattern Interferometry has been successfully used during tensile testing of semi-hard copper sheets in order tomeasure the strain rate. On one hand, heterogeneity in strain rate field has been found before the maximum of the tensile force ( e t 19.4 and25.4%, respectively). Thus, a localization phenomenon occurs before the classic Consid`ere’s criterion (d F =0) for the diffuse neck initiation. Onthe other hand, strain rate measurement before fracture shows the moment where one of the two slip band systems becomes predominant, thenstrain concentrates in a small area, the shear band. Uncertainty evaluation has been carried out, which shows a very good accuracy of the totalstrain and the strain rate measurements.© 2005 Elsevier B.V. All rights reserved. Keywords: Tensile test; ESPI; Strain rate measurement; Strain localization; Necking; Uncertainty determination 1. Introduction Thetensiletestisprobablythemostcommonlyusedmechan-ical test. It allows determining many mechanical properties ofmaterials, such as Young’s modulus, yield stress, tensile stress,strain hardening coefficient and ductility. Many metals exhibittensile stress–strain curves whose initial linear portion (elasticregion) passes gradually to the elasto-plastic region. In a firststage of the latter, strains are homogeneous along the speci-men. This stage ends when a diffuse neck appears. Classically,it is considered [1] that the diffuse neck occurs when the forcereaches its maximum. Then, strains begin to be heterogenous upto the localized neck, which is a shear band for a sheet in uniax-ial tensile test, whose width is of the same order of magnitudeas the specimen thickness.Several theoretical models have been developed since the1950s [2–12]. Swift [2] has proposed a criterion for the deter-mination of the maximum principal stress generating the plastic