The Experts below are selected from a list of 228 Experts worldwide ranked by ideXlab platform
Suzanne M Fielding - One of the best experts on this subject based on the ideXlab platform.
-
criteria for extensional Necking Instability in complex fluids and soft solids part ii imposed tensile stress and force protocols
Journal of Rheology, 2016Co-Authors: David M Hoyle, Suzanne M FieldingAbstract:We study the Necking of a filament of complex fluid or soft solid subject to uniaxial tensile stretching, separately under conditions of constant imposed tensile stress and constant imposed tensile force, by means of linear stability analysis and nonlinear simulations at the level of a slender filament approximation. We demonstrate Necking to be a flow Instability that arises as an unavoidable consequence of the viscoelastic constitutive behavior of essentially any material (with a possible rare exception). We derive criteria for the onset of Necking that can be reported in terms of characteristic signatures in the shapes of the experimentally measured material functions, and that should therefore apply universally to all viscoelastic materials. To confirm their generality, we show them to hold numerically in six constitutive models: The Oldroyd B, Giesekus, nonstretch Rolie-Poly, finite-stretch Rolie-Poly and Pom-pom models, and a simplified toy model of coil-stretch hysteresis, which has a nonmonotonic underlying extensional constitutive curve. Under conditions of constant imposed tensile stress, we find two distinct dynamical regimes as a function of the time since the inception of the flow. In the first regime the strain rate quickly attains a value prescribed by the fluid's underlying stationary homogeneous extensional constitutive curve, at the given imposed stress. During this first regime, no appreciable (or only minimal) Necking arises. A second regime then ensues in which the initial homogeneous flow destabilizes to form a neck. This Necking Instability can occur via two distinct possible modes. The first mode is relatively gentle and arises in any regime where the slope of the extensional constitutive curve is positive. It has a rate of Necking per accumulated strain unit set by the inverse of the slope of the constitutive curve on a log-log plot. The second mode sets in when a carefully defined “elastic derivative” of the tensile force first slopes down as a function of the time (or accumulated strain) since the inception of the flow. We discuss the way in which these modes of Instability manifest themselves in entangled polymeric fluids, demonstrating four distinct regimes of Necking behavior as a function of imposed stress. Under conditions of constant imposed tensile force, typically the flow sweeps up the underlying constitutive curve of the fluid in question, again with Instability to Necking in any regime where that curve is positively sloping.
-
criteria for extensional Necking Instability in complex fluids and soft solids part i imposed hencky strain rate protocol
Journal of Rheology, 2016Co-Authors: David M Hoyle, Suzanne M FieldingAbstract:We study theoretically the Necking dynamics of a filament of complex fluid or soft solid in uniaxial tensile stretching at constant imposed Hencky strain rate ϵ , by means of linear stability analysis and nonlinear (slender filament) simulations. We demonstrate Necking to be an intrinsic flow Instability that arises as an inevitable consequence of the constitutive behavior of essentially any material (with a possible rare exception, which we outline), however carefully controlled the experimental conditions. We derive criteria for the onset of Necking that are reportable simply in terms of characteristic signatures in the shapes of the experimentally measured rheological response functions, and should therefore apply universally to all materials. As evidence of their generality, we show them to hold numerically in six popular constitutive models: The Oldroyd B, Giesekus, FENE-CR, Rolie-Poly, and Pom-pom models of polymeric fluids, and a fluidity model of soft glassy materials. Two distinct modes of neck...
-
age dependent modes of extensional Necking Instability in soft glassy materials
Physical Review Letters, 2015Co-Authors: David M Hoyle, Suzanne M FieldingAbstract:Many soft materials, including foams, emulsions, microgels and colloids comprise disordering packings of mesoscopic substructures: foam bubbles, emulsion droplets, etc. At high volume fractions, the local rearrangement dynamics of these are impeded by large energy barriers and show a glassy slowing down. This underpins many universal features in the rheological (deformation and flow) properties of these “soft glassy materials” (SGMs). Particularly striking is the phenomenon of rheological ageing, in which an initially liquid-like sample slowly evolves towards an ever more solid-like state as a function of the time since it was prepared. In the last decade, significant progress has been made in understanding the role of ageing in the shear flow of SGMs [1]. Similar phenomena have been explored in polymeric [2] and metallic [3] glasses, with many unifying features across all these amorphous, elastoplastic materials. Much less is understood about the response of these materials to extensional deformations, which are important to industrial processes in fibre spinning, inkjetting, porous media, and the peeling and tack of surfaces bonded by adhesives. In the standard experimental test, an initially near uniform cylindrical (or rectangular) sample is steadily drawn out in length, with the aim of measuring the tensile stress as a function of strain and
-
criterion for extensional Necking Instability in polymeric fluids
Physical Review Letters, 2011Co-Authors: Suzanne M FieldingAbstract:: We study the linear Instability with respect to Necking of a filament of polymeric fluid undergoing uniaxial extension. Contrary to the widely discussed Considere criterion, we find the onset of Instability to relate closely to the onset of downward curvature in the time (and so strain) evolution of the zz component of the molecular strain, for extension along the z axis. In establishing this result numerically across five of the most widely used models of polymer rheology, and by analytical calculation, we argue it to apply generically. Particularly emphasized is the importance of polymer chain stretching in partially mitigating Necking. We comment finally on the relationship between Necking and the shape of the underlying steady state constitutive curve for homogeneous extension.
Ronald C Hedden - One of the best experts on this subject based on the ideXlab platform.
-
Necking Instability during Polydomain−Monodomain Transition in a Smectic Main-Chain Elastomer
Macromolecules, 2009Co-Authors: Harshad P Patil, Daniel M Lentz, Ronald C HeddenAbstract:The mechanical response and the evolution of director orientation are characterized in a smectic, main-chain liquid crystalline elastomer (LCE) as it undergoes the familiar polydomain−monodomain (P−M) transition. Under uniaxial tension, the LCE behaves like an ordinary rubber-like network at low strains, and local director rotations are shown to slightly favor the perpendicular (“anomalous”) orientation of chain axes with respect to the draw direction. As strain increases, a well-defined yield stress is observed due to the onset of a Necking Instability. Macroscopic elongation proceeds by growth of the necked monodomain region, which appears to consume the non-necked polydomain region(s) at its boundaries. Within the necked region, the parallel (“normal”) orientation of chain axes with respect to the draw direction is strongly favored. The P−M transition is attributed to a change in the conformation of the elastic polymer backbones from hairpinned coils to extended chains. Under the conditions of temperat...
-
Necking Instability during polydomain monodomain transition in a smectic main chain elastomer
Macromolecules, 2009Co-Authors: Harshad P Patil, Daniel M Lentz, Ronald C HeddenAbstract:The mechanical response and the evolution of director orientation are characterized in a smectic, main-chain liquid crystalline elastomer (LCE) as it undergoes the familiar polydomain−monodomain (P−M) transition. Under uniaxial tension, the LCE behaves like an ordinary rubber-like network at low strains, and local director rotations are shown to slightly favor the perpendicular (“anomalous”) orientation of chain axes with respect to the draw direction. As strain increases, a well-defined yield stress is observed due to the onset of a Necking Instability. Macroscopic elongation proceeds by growth of the necked monodomain region, which appears to consume the non-necked polydomain region(s) at its boundaries. Within the necked region, the parallel (“normal”) orientation of chain axes with respect to the draw direction is strongly favored. The P−M transition is attributed to a change in the conformation of the elastic polymer backbones from hairpinned coils to extended chains. Under the conditions of temperat...
Teng Li - One of the best experts on this subject based on the ideXlab platform.
-
Deformability of thin metal films on elastomer substrates
International Journal of Solids and Structures, 2020Co-Authors: Teng LiAbstract:AbstractRecent applications in flexible electronics require that thin metal films grown on elastomer substrates be deformable. However, how such laminates deform is poorly understood. While a freestanding metal film subject to tension will rupture at a small strain by undergoing a Necking Instability, we anticipate that a substrate will retard this Instability to an extent that depends on the relative stiffness and thickness of the film and the substrate. Using a combination of a bifurcation analysis and finite element simulations, we identify three modes of tensile deformation. On a compliant elastomer, a metal film forms a neck and ruptures at a small strain close to that of a freestanding film. On a stiff elastomer, the metal film deforms uniformly to large strains. On an elastomer of intermediate compliance, the metal film forms multiple necks, deforms much beyond the initial bifurcation, and ruptures at a large strain. Our theoretical predictions call for new experiments
-
Necking limit of substrate-supported metal layers under biaxial in-plane loading
International Journal of Plasticity, 2013Co-Authors: Teng LiAbstract:Necking Instability often indicates the onset of ductile failure. It has been shown that the Necking Instability in a substrate-supported metal layer can be retarded to a higher strain than that in a single freestanding metal layer. Most existing theoretical studies of the neck- ing limit of substrate-supported metal layers assume plane strain condition. However, most commonly conducted experiments of such metal/substrate bilayers are uniaxial ten- sile tests. So far, the Necking Instability of substrate-supported metal layers under arbitrary combinations of biaxial in-plane loading conditions remains poorly understood. This paper presents a comprehensive study of the Necking limit of a metal/substrate bilayer over the full range of biaxial loading ratio, from 1 for equibiaxial loading, to 0 for plane strain load- ing, and to � 1/2 for uniaxial loading. Two representative material combinations are consid- ered, namely, a metal layer supported by a stiff plastic substrate, and a metal layer supported by a compliant elastomer substrate. The results quantitatively correlate both critical Necking limit strain and Necking band orientation with the material properties and thickness ratio of the substrate-metal bilayer. In particular, the predicted Necking band orientation when the bilayer is under in-plane loading with a negative ratio (e.g., uniaxial tension) agrees with the slanted Necking bands observed in experiments, a phenomenon that cannot be explained by existing theoretical studies assuming plane strain condition. The present study further shows that Necking retardation in an elastomer-supported metal layer can allow the bilayer to absorb and dissipate more energy than an all-metal single layer with the same mass. These understandings shed light on optimal design of sub- strate-supported metal structures with enhanced deformability and energy absorbing capacity under complex in-plane loading conditions.
-
Stretchability of thin metal films on elastomer substrates
Applied Physics Letters, 2004Co-Authors: Teng Li, Zhigang Suo, St́phanie P. Lacour, Zhenyu Huang, Sigurd WagnerAbstract:Recent applications in flexible electronics require that thin metal films grown on elastomer substrates be deformable. However, how such laminates deform is poorly understood. While a freestanding metal film subject to tension will rupture at a small strain by undergoing a Necking Instability, we anticipate that a substrate will retard this Instability to an extent that depends on the relative stiffness and thickness of the film and the substrate. Using a combination of a bifurcation analysis and finite element simulations, we identify three modes of tensile deformation. On a compliant elastomer, a metal film forms a neck and ruptures at a small strain close to that of a freestanding film. On a stiff elastomer, the metal film deforms uniformly to large strains. On an elastomer of intermediate compliance, the metal film forms multiple necks, deforms much beyond the initial bifurcation, and ruptures at a large strain. Our theoretical predictions call for new experiments. © 2005 Elsevier Ltd. All rights reserved.
Sigurd Wagner - One of the best experts on this subject based on the ideXlab platform.
-
Stretchability of thin metal films on elastomer substrates
Applied Physics Letters, 2004Co-Authors: Teng Li, Zhigang Suo, St́phanie P. Lacour, Zhenyu Huang, Sigurd WagnerAbstract:Recent applications in flexible electronics require that thin metal films grown on elastomer substrates be deformable. However, how such laminates deform is poorly understood. While a freestanding metal film subject to tension will rupture at a small strain by undergoing a Necking Instability, we anticipate that a substrate will retard this Instability to an extent that depends on the relative stiffness and thickness of the film and the substrate. Using a combination of a bifurcation analysis and finite element simulations, we identify three modes of tensile deformation. On a compliant elastomer, a metal film forms a neck and ruptures at a small strain close to that of a freestanding film. On a stiff elastomer, the metal film deforms uniformly to large strains. On an elastomer of intermediate compliance, the metal film forms multiple necks, deforms much beyond the initial bifurcation, and ruptures at a large strain. Our theoretical predictions call for new experiments. © 2005 Elsevier Ltd. All rights reserved.
Harshad P Patil - One of the best experts on this subject based on the ideXlab platform.
-
Necking Instability during Polydomain−Monodomain Transition in a Smectic Main-Chain Elastomer
Macromolecules, 2009Co-Authors: Harshad P Patil, Daniel M Lentz, Ronald C HeddenAbstract:The mechanical response and the evolution of director orientation are characterized in a smectic, main-chain liquid crystalline elastomer (LCE) as it undergoes the familiar polydomain−monodomain (P−M) transition. Under uniaxial tension, the LCE behaves like an ordinary rubber-like network at low strains, and local director rotations are shown to slightly favor the perpendicular (“anomalous”) orientation of chain axes with respect to the draw direction. As strain increases, a well-defined yield stress is observed due to the onset of a Necking Instability. Macroscopic elongation proceeds by growth of the necked monodomain region, which appears to consume the non-necked polydomain region(s) at its boundaries. Within the necked region, the parallel (“normal”) orientation of chain axes with respect to the draw direction is strongly favored. The P−M transition is attributed to a change in the conformation of the elastic polymer backbones from hairpinned coils to extended chains. Under the conditions of temperat...
-
Necking Instability during polydomain monodomain transition in a smectic main chain elastomer
Macromolecules, 2009Co-Authors: Harshad P Patil, Daniel M Lentz, Ronald C HeddenAbstract:The mechanical response and the evolution of director orientation are characterized in a smectic, main-chain liquid crystalline elastomer (LCE) as it undergoes the familiar polydomain−monodomain (P−M) transition. Under uniaxial tension, the LCE behaves like an ordinary rubber-like network at low strains, and local director rotations are shown to slightly favor the perpendicular (“anomalous”) orientation of chain axes with respect to the draw direction. As strain increases, a well-defined yield stress is observed due to the onset of a Necking Instability. Macroscopic elongation proceeds by growth of the necked monodomain region, which appears to consume the non-necked polydomain region(s) at its boundaries. Within the necked region, the parallel (“normal”) orientation of chain axes with respect to the draw direction is strongly favored. The P−M transition is attributed to a change in the conformation of the elastic polymer backbones from hairpinned coils to extended chains. Under the conditions of temperat...
