scholarly journals Anomalous first normal stress difference behavior of polymer nanocomposites and liquid crystalline polymer composites

2013 ◽  
Vol 54 (6) ◽  
pp. 1300-1312 ◽  
Author(s):  
Esmaeil Narimissa ◽  
Ahmed Rahman ◽  
Rahul K. Gupta ◽  
Nhol Kao ◽  
Sati N. Bhattacharya
Keyword(s):  
Normal Stress ◽  
Polymer Composites ◽  
Polymer Nanocomposites ◽  
Liquid Crystalline Polymer ◽  
Liquid Crystalline ◽  
Crystalline Polymer ◽  
Normal Stress Difference ◽  
Stress Difference ◽  
First Normal Stress Difference

Rheology of LCP/PET Blends at Solid and Molten States of LCP

2006 ◽  
Vol 16 (3) ◽  
pp. 152-160 ◽  
Author(s):  
S.A.R. Hashmi ◽  
Takeshi Kitano
Keyword(s):  
Shear Stress ◽  
Normal Stress ◽  
Shear Viscosity ◽  
Liquid Crystalline ◽  
High Sensitivity ◽  
Crystalline Polymer ◽  
Normal Stress Difference ◽  
Stress Difference ◽  
First Normal Stress Difference ◽  
Different Temperatures

Abstract Liquid crystalline polymer (LCP) and polyethylene terephthalate (PET) were blended in an elastic melt extruder to make samples having different volume fractions of constituent polymers. Shear stress, shear viscosity, first normal stress difference at different shear rates under steady state conditions of these blends were evaluated at two different temperatures 265 and 285˚C. The LCP was in solid state at 265˚C and in melt state at 285˚C and was dispersed in molten matrix of PET at both temperatures. Shear viscosity of blend increased with addition of LCP in PET matrix. A maxima was observed in viscosity versus composition plot. Blends containing more than 50 vol. % of LCP in the blend show higher viscosity as compared to the constituent polymers. First normal stress difference, N1, increased with LCP content in the blend at 285˚C when ploted against shear stress whereas at 265˚C this trend was opposite. The increased value of N1 with shear rate was explained assuming a tendency of asymmetric particles to rotate under velocity gradient of suspending medium. At 285˚C N1 varied with shear stress in two stages. First stage was characterized with high sensitivity of N1 with shear stress, which reduced in second stage on plastic deformation of LCP droplets.

The first normal stress difference of non-Brownian hard-sphere suspensions in the oscillatory shear flow near the liquid and crystal coexistence region

Soft Matter ◽  
2020 ◽  
Vol 16 (43) ◽  
pp. 9864-9875
Author(s):  
Young Ki Lee ◽  
Kyu Hyun ◽  
Kyung Hyun Ahn
Keyword(s):  
Shear Flow ◽  
Normal Stress ◽  
Hard Sphere ◽  
Normal Stress Difference ◽  
Oscillatory Shear ◽  
Stress Difference ◽  
Large Amplitude Oscillatory Shear ◽  
First Normal Stress Difference ◽  
Oscillatory Shear Flow ◽  
Sphere Suspensions

The first normal stress difference (N1) as well as shear stress of non-Brownian hard-sphere suspensions in small to large amplitude oscillatory shear flow is investigated.

Effect of Inner Cavity’s Gas Flow Rate on the Extrusion Forming of Plastic Micro-Pipe

2020 ◽  
Vol 842 ◽  
pp. 279-284
Author(s):  
Zhong Ren ◽  
Xing Yuan Huang
Keyword(s):  
Finite Element ◽  
Normal Stress ◽  
Flow Rate ◽  
Gas Flow ◽  
Normal Stress Difference ◽  
Stress Difference ◽  
Gas Flow Rate ◽  
Flow Rates ◽  
First Normal Stress Difference ◽  
Extrusion Forming

During the manufacture of plastic micro-pipe, a certain volume of gas should be properly injected into the inner cavity to overcome the collapse and adhesion problems. In this work, the extrusion forming of plastic micro-tube under the role of inner cavity’s gas were numerically studied. At the same time, the effect of inner cavity’s gas flow rate on the extrusion deformation of plastic micro-pipe was also numerically investigated by using the finite element method. A kind of 2D two-phase fluid geometric model and finite element mesh were established and some reasonable boundary conditions and material parameters were imposed. Under a fixed volume flow rate of melt, different flow rates of inner cavity gas were imposed on the inlet of inner cavity’s gas. The extrusion deformation profile and deformation ratio of plastic micro-pipe under different flow rates of gas were all obtained. To ascertain the mechanisms of effect of inner cavity’s gas flow rate on the extrusion deformation of plastic micro-tube, the flow velocities, pressure, shear rate, normal stress, and the first normal stress difference of melt all obtained and analyzed. Numerical results show that with the increase of inner cavity’s gas flow rate, the radial velocity, axial velocity, pressure, shear rate, normal stress, and the first normal stress difference of melt all increase, which makes the extrusion deformation become more and more serious. In practice, reasonable controlling of the inner cavity’s gas flow rate is very important. In the other hand, it can adjust the size of extruded plastic micro-pipe.

Normal stresses and microstructure in bounded sheared suspensions via Stokesian Dynamics simulations

2000 ◽  
Vol 412 ◽  
pp. 279-301 ◽  
Author(s):  
ANUGRAH SINGH ◽  
PRABHU R. NOTT
Keyword(s):  
Normal Stress ◽  
Couette Flow ◽  
Normal Stress Difference ◽  
Stress Difference ◽  
Normal Stresses ◽  
Plane Couette Flow ◽  
Stokesian Dynamics ◽  
First Normal Stress Difference ◽  
Particle Pressure ◽  
Dynamics Simulations

We report the normal stresses in a non-Brownian suspension in plane Couette flow determined from Stokesian Dynamics simulations. The presence of normal stresses that are linear in the shear rate in a viscometric flow indicates a non-Newtonian character of the suspension, which is otherwise Newtonian. While in itself of interest, this phenomenon is also important because it is believed that normal stresses determine the migration of particles in flows with inhomogeneous shear fields. We simulate plane Couette flow by placing a layer of clear fluid adjacent to one wall in the master cell, which is then replicated periodically. From a combination of the traceless hydrodynamic stresslet on the suspended particles, the stresslet due to (non-hydrodynamic) inter-particle forces, and the total normal force on the walls, we determine the hydrodynamic and inter-particle force contributions to the isotropic ‘particle pressure’ and the first normal stress difference. We determine the stresses for a range of the particle concentration and the Couette gap. The particle pressure and the first normal stress difference exhibit a monotonic increase with the mean particle volume fraction ϕ. The ratio of normal to shear stresses on the walls also increases with ϕ, substantiating the result of Nott & Brady (1994) that this condition is required for stability to concentration fluctuations. We also study the microstructure by extracting the pair distribution function from our simulations; our results are in agreement with previous studies showing anisotropy in the pair distribution, which is the cause of normal stresses.

Rheological Properties of Carbon Fiber and Carbon Black Filled Liquid Crystalline Polymer Melts

2001 ◽  
Vol 11 (4) ◽  
pp. 188-196 ◽  
Author(s):  
Katsuhiko Araki ◽  
Takeshi Kitano ◽  
Berenika Hausnerova
Keyword(s):  
Shear Rate ◽  
Carbon Fiber ◽  
Carbon Black ◽  
Liquid Crystalline Polymer ◽  
Liquid Crystalline ◽  
Filler Content ◽  
Crystalline Polymer ◽  
Normal Stress Difference ◽  
Steady Shear Viscosity ◽  
Rate Region

Abstract The rheological properties of thermotropic liquid crystalline polymer (LCP) and its carbon fiber (CF) and carbon black (CB) filled composites in molten state were measured using a cone-plate rheometer. The measurements of the CF/LCP and CB/LCP melts were performed with carbon fiber contents of 5, 10 and 20 wt %, and carbon black contents of 1.5, 3, 5, 10 and 20 wt %. As expected, steady shear viscosity of the LCP, CF/LCP and CB/LCP melts in a low shear rate region (0.1 to 1 s-1) decreased with an increase of temperature and increased with rise of filler content. In shear rate region of 1 to 50 s-1, the LCP melt showed a unique viscosity behaviour with maximum and minimum values. The CF/LCP and CB/LCP melts showed disappearance of such a unique viscosity behaviour with an increase in the CF (CB) content and an increase of temperature. CB filler had a more pronounced effect on the disappearance of the unique viscosity behaviour in comparison with CF. Regarding apparent yield stress, the CF/LCP melts gave the same value as pure LCP, the CB/LCP melts showed an increase of yield with a rise of the filler content. In addition, the first normal stress difference of the LCP and CF/LCP melts are smaller than yield stress values, although the rate of increase with shear rate is higher in case of normal stress difference than in case of yield. The results of the dynamic shear oscillatory flow measurements of CF and CB based compounds at 300˚C showed that both, the storage and loss moduli are more affected by carbon black filler. Complex viscosity values of the LCP and CF/LCP melts showed no such unique complex flow pattern as observed in the case of steady shear viscosity.

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