scholarly journals Stress relaxation following uniaxial extension of polystyrene melt and oligomer dilutions

2016 ◽  
Vol 60 (3) ◽  
pp. 465-471 ◽  
Author(s):  
Qian Huang ◽  
Henrik Koblitz Rasmussen
Keyword(s):  
Stress Relaxation ◽  
Uniaxial Extension ◽  
Polystyrene Melt

scholarly journals Stress relaxation and reversed flow of low-density polyethylene melts following uniaxial extension

2012 ◽  
Vol 56 (6) ◽  
pp. 1535-1554 ◽  
Author(s):  
Qian Huang ◽  
Henrik K. Rasmussen ◽  
Anne L. Skov ◽  
Ole Hassager
Keyword(s):  
Stress Relaxation ◽  
Uniaxial Extension ◽  
Low Density Polyethylene ◽  
Low Density ◽  
Reversed Flow ◽  
Polyethylene Melts

Stress relaxation after a step strain in uniaxial extension of polyisobutylene and polyethylene

2003 ◽  
Vol 42 (4) ◽  
pp. 345-354 ◽  
Author(s):  
Vitor C. Barroso ◽  
Sandra P. Ribeiro ◽  
Jo�o M. Maia
Keyword(s):  
Stress Relaxation ◽  
Uniaxial Extension ◽  
Step Strain

Free Edge Stresses in Elastic and Viscoelastic Composites Under Uniaxial Extension, Bending, and Twisting Loadings

1997 ◽  
Vol 119 (3) ◽  
pp. 266-272 ◽  
Author(s):  
Sung Yi ◽  
H. H. Hilton
Keyword(s):  
Stress Relaxation ◽  
Constitutive Relations ◽  
Plane Deformation ◽  
Uniaxial Extension ◽  
Free Edge ◽  
Time Dependent ◽  
Interlaminar Stresses ◽  
Shear Moduli ◽  
Deformation State ◽  
Interlaminar Shear

Time-dependent interlaminar stresses in elastic and viscoelastic laminated composites subjected to arbitrary combinations of axial extension, bending and/or twisting loads are obtained based on integral constitutive relations and Pipes and Pagano’s displacement field for laminates under a generalized plane deformation state. Numerical results obtained from the present formulation are compared against experimental data and excellent agreement within two percent was obtained between these results. Time-dependent interlaminar stresses for cross-ply and angle-ply laminates subjected to uniaxial extension, bending and twisting are also presented. Appreciable stress relaxation occurred during the loading period resulting in decreased magnitudes of residual stresses. It is seen that the rate of interlaminar shear stress relaxation is greater than the normal one, since the relaxation of shear moduli is larger than that of the normal moduli.

scholarly journals Stress relaxation of narrow molar mass distribution polystyrene following uniaxial extension

2008 ◽  
Vol 52 (4) ◽  
pp. 885-899 ◽  
Author(s):  
Jens Kromann Nielsen ◽  
Henrik Koblitz Rasmussen ◽  
Ole Hassager
Keyword(s):  
Stress Relaxation ◽  
Mass Distribution ◽  
Molar Mass ◽  
Uniaxial Extension ◽  
Molar Mass Distribution

scholarly journals Toward understanding thrombus fracture: Dissipative phenomena of whole blood clots

2020 ◽  
Author(s):  
Gabriella P. Sugerman ◽  
Sapun H. Parekh ◽  
Manuel K. Rausch
Keyword(s):  
Stress Relaxation ◽  
Whole Blood ◽  
Room Temperature ◽  
Uniaxial Extension ◽  
Future Studies ◽  
Intensive Care Patients ◽  
Nonlinear Stress ◽  
Blood Clots ◽  
Submerged Conditions

When thrombus fractures and breaks off it can occlude vital vessels such as those of the heart, lung, or brain. These thromboembolic conditions are responsible for 1 in 4 deaths world-wide. This problem is also of significant current interest as 1 in 3 COVID-19 intensive care patients exhibit thromboembolic complications. Thrombus resistance to fracture is driven by its intrinsic fracture toughness as well as other, non-surface-creating dissipative mechanisms. In our current work, we identify and quantify these latter mechanisms toward future studies that aim to delineate fracture from other forms of dissipation. To this end, we use an in vitro thrombus mimic system to produce whole blood clots and explore their dissipative mechanics under simple uniaxial extension, cyclic loading, and stress-relaxation. We found that whole blood clots exhibit Mullins effect, hysteresis, permanent set, strain-rate dependence, and nonlinear stress-relaxation. Interestingly, we found that performing these tests under dry or submerged conditions did not change our results. However, performing these tests under room temperature or body temperature conditions yielded differences. Overall, we have demonstrated that whole blood clots show several dissipative phenomena - similarly to hydrogels - that will be critical to our understanding of thrombus fracture.

scholarly journals Stress relaxation in a dilute bacterial suspension: the active–passive transition

2019 ◽  
Vol 870 ◽  
pp. 1072-1104 ◽  
Author(s):  
Sankalp Nambiar ◽  
Phanikanth S. ◽  
P. R. Nott ◽  
Ganesh Subramanian
Keyword(s):  
Kinetic Equation ◽  
Stress Relaxation ◽  
Simple Shear ◽  
Uniaxial Extension ◽  
Bacterial Suspension ◽  
Simple Shear Flow ◽  
Rheological Response ◽  
Step Initiation ◽  
Passive Transition ◽  
Rotary Diffusion

This paper follows a recent article of Nambiar et al. (J. Fluid Mech., vol. 812, 2017, pp. 41–64) on the linear rheological response of a dilute bacterial suspension (e.g. E. coli) to impulsive starting and stopping of simple shear flow. Here, we analyse the time dependent nonlinear rheology for a pair of linear flows – simple shear (a canonical weak flow) and uniaxial extension (a canonical strong flow), again in response to impulsive initiation and cessation. The rheology is governed by the bacterium orientation distribution which satisfies a kinetic equation that includes rotation by the imposed flow, and relaxation to isotropy via rotary diffusion and tumbling. The relevant dimensionless parameters are the Péclet number $Pe\equiv \dot{\unicode[STIX]{x1D6FE}}\unicode[STIX]{x1D70F}$, which dictates the importance of flow-induced orientation anisotropy, and $\unicode[STIX]{x1D70F}D_{r}$, which quantifies the relative importance of the two intrinsic orientation decorrelation mechanisms (tumbling and rotary diffusion). Here, $\unicode[STIX]{x1D70F}$ is the mean run duration of a bacterium that exhibits a run-and-tumble dynamics, $D_{r}$ is the intrinsic rotary diffusivity of the bacterium and $\dot{\unicode[STIX]{x1D6FE}}$ is the characteristic magnitude of the imposed velocity gradient. The solution of the kinetic equation is obtained numerically using a spectral Galerkin method, that yields the rheological properties (the shear viscosity, the first and second normal stress differences for simple shear, and the extensional viscosity for uniaxial extension) over the entire range of $Pe$. For simple shear, we find that the stress relaxation predicted by our analysis at small $Pe$ is in good agreement with the experimental observations of Lopez et al. (Phys. Rev. Lett., vol. 115, 2015, 028301). However, the analysis at large $Pe$ yields relaxations that are qualitatively different. Upon step initiation of shear, the rheological response in the experiments corresponds to a transition from a nearly isotropic suspension of active swimmers at small $Pe$, to an apparently (nearly) isotropic suspension of passive rods at large $Pe$. In contrast, the computations yield the expected transition to a nearly flow-aligned suspension of passive rigid rods at high $Pe$. We probe this active–passive transition systematically, complementing the numerical solution with analytical solutions obtained from perturbation expansions about appropriate base states. Our study suggests courses for future experimental and analytical studies that will help understand relaxation phenomena in active suspensions.

Stress Relaxation and the Formation of Silicides in the Process of the Crystallization of NI-NB Films on SI

1991 ◽  
Vol 49 ◽  
pp. 898-899
Author(s):  
N. Rozhanski ◽  
V. Lifshitz
Keyword(s):  
Thin Films ◽  
Stress Relaxation ◽  
Integrated Circuits ◽  
Direct Evidence ◽  
Alloy Film ◽  
Diffusion Barriers ◽  
Effective Barrier

Thin films of amorphous Ni-Nb alloys are of interest since they can be used as diffusion barriers for integrated circuits on Si. A native SiO2 layer is an effective barrier for Ni diffusion but it deformation during the crystallization of the alloy film lead to the appearence of diffusion fluxes through it and the following formation of silicides. This study concerns the direct evidence of the action of stresses in the process of the crystallization of Ni-Nb films on Si and the structure of forming NiSi2 islands.

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