Modeling and Simulation of Suction Blow Molding Process for Producing Curved Ducts

During suction blow molding process, the extruded parison undergoes twisting deformation within the mold cavity, as the air drawing flow around the deforming parison exerts non-uniform shear stresses on its surface. This research is devoted in developing a fluid-structure interaction model for predicting parison deformation during suction blow molding process, with a specific emphasis on the suction stage. A fluid flow model, based on Hele-Shaw approximations, is formulated to simulate the air drag force exerted on the parison surface. The rheology of the polymer during suction is assumed to obey the K-BKZ integral viscoelastic model. The numerical results of this study allowed identifying a clear correlation between the twisting deformation undergone by the parison during the suction stage, also observed experimentally and the design parameters, namely, the air suction speed, the geometry of the duct mold cavity, and the parison/mold eccentricity

Modeling of large area hot embossing

Today, hot embossing and injection molding belong to the established plastic molding processes in microengineering. Based on experimental findings, a variety of microstructures have been replicated so far using the processes. However, with increasing requirements regarding the embossing surface and the simultaneous decrease of the structure size down into the nanorange, increasing know-how is needed to adapt hot embossing to industrial standards. To reach this objective, a German-Canadian cooperation project has been launched to study hot embossing theoretically by a process simulation and experimentally. The present publication shall report about the first results of the simulation - the modeling and simulation of large area replication based on an eight inch microstructured mold.Comment: Submitted on behalf of EDA Publishing Association (http://irevues.inist.fr/EDA-Publishing

Nonequilibrium stretching dynamics of dilute and entangled linear polymers in extensional flow

We propose an extension of the FENE-CR model for dilute polymer solutions [M. D. Chilcott, J. M. Rallison, Creeping flow of dilute polymer solutions past cylinders and spheres, J. Non-Newtonian Fluid Mech. 29 (1988) 382-432] and the Rouse-CCR tube model for linear entangled polymers [A. E. Likhtman, R. S. Graham, Simple constitutive equation for linear polymer melts derived from molecular theory: Rolie-Poly equation, J. Non-Newtonian Fluid Mech. 114 (2003) 1-12], to describe the nonequilibrium stretching dynamics of polymer chains in strong extensional flows. The resulting models, designed to capture the progressive changes in the average internal structure (kinked state) of the polymer chain, include an 'effective' maximum contour length that depends on local flow dynamics. The rheological behavior of the modified models is compared with various results already published in the literature for entangled polystyrene solutions, and for the Kramers chain model (dilute polymer solutions). It is shown that the FENE-CR model with an 'effective' maximum contour length is able to describe correctly the hysteric behaviour in stress versus birefringence in start-up of uniaxial extensional flow and subsequent relaxation also observed and computed by Doyle et al. [P. S. Doyle, E. S. G. Shaqfeh, G. H. McKinley, S. H. Spiegelberg, Relaxation of dilute polymer solutions following extensional flow, J. Non-Newtonian Fluid Mech. 76 (1998) 79-110] and Li and Larson [L. Li, R. G. Larson, Excluded volume effects on the birefringence and stress of dilute polymer solutions in extensional flow, Rheol. Acta 39 (2000) 419-427] using Brownian dynamics simulations of bead-spring model. The Rolie-Poly model with an 'effective' maximum contour length exhibits a less pronounced hysteretic behavior in stress versus birefringence in start-up of uniaxial extensional flow and subsequent relaxationNous proposons une extension du mod\ue8le FENE-CR pour des solutions de polym\ue8re dilu\ue9es [M.D. Chilcott, J.M. Rallison, Creeping flow of dilute polymer solutions past cylinders and spheres, J. Non-Newtonian Fluid Mech. 29 (1988) 382\u2013432] et le mod\ue8le de tube Rouse-CCR pour des polym\ue8res lin\ue9aires entrem\ueal\ue9s [A.E. Likhtman, R.S. Graham, Simple constitutive equation for linear polymer melts derived from molecular theory: Rolie\u2013Poly equation, J. Non-Newtonian Fluid Mech. 114 (2003) 1\u201312] pour d\ue9crire la dynamique d\u2019\ue9tirement hors \ue9quilibre de cha\ueenes de polym\ue8res dans des \ue9coulements d\u2019extension puissants. Les mod\ue8les ainsi obtenus, con\ue7us pour capturer les modifications progressives dans la structure interne moyenne (\ue9tat coud\ue9) de la cha\ueene polym\ue8re, comprennent une longueur maximale de contour \uab efficace \ubb qui d\ue9pend de la dynamique d\u2019\ue9coulement locale. Le comportement rh\ue9ologique des mod\ue8les modifi\ue9s est compar\ue9 \ue0 divers r\ue9sultats d\ue9j\ue0 publi\ue9s dans la litt\ue9rature pour des solutions de polystyr\ue8ne entrem\ueal\ue9 et pour le mod\ue8le de cha\ueene de Kramers (solutions de polym\ue8res dilu\ue9es). On montre que le mod\ue8le FENE-CR avec une longueur de contour maximale \uab efficace \ubb permet de d\ue9crire correctement le comportement d\u2019hyst\ue9r\ue8se sous contrainte par rapport \ue0 la bir\ue9fringence lors du d\ue9marrage de l\u2019\ue9coulement d\u2019extension uniaxial et de la relaxation subs\ue9quente \ue9galement observ\ue9e et calcul\ue9e par Doyle et coll. [P.S. Doyle, E.S.G. Shaqfeh, G.H. McKinley, S.H. Spiegelberg, Relaxation of dilute polymer solutions following extensional flow, J. Non-Newtonian Fluid Mech. 76 (1998) 79\u2013110] et par Li et Larson [L. Li, R.G. Larson, Excluded volume effects on the birefringence and stress of dilute polymer solutions in extensional flow, Rheol. Acta 39 (2000) 419\u2013427] au moyen de simulations en dynamique brownienne de mod\ue8le bille/ressort. Le mod\ue8le de Rolie\u2013Poly avec une longueur de contour maximale \uab efficace \ubb exhibe un comportement d\u2019hyst\ue9r\ue8se moins prononc\ue9 sous contrainte par rapport \ue0 la bir\ue9fringence lors du d\ue9marrage de l\u2019\ue9coulement d\u2019extension uniaxial et lors de la relaxation subs\ue9quente.Peer reviewed: YesNRC publication: Ye

Optimal Design For Injection Molding

Peer reviewed: YesNRC publication: Ye

Start-up of Flow Through a 4:1:4 Constriction in a Tube Using the Rouse-CCR Tube Model for Linear Entangled Polymers with Finite Extensibility

Peer reviewed: YesNRC publication: Ye

Elastic flow-front fingering instability in flowing polymer solutions

An experimental investigation of the flow-front behavior of dilute and semi-dilute polymer solutions has been carried out to gain a better understanding of the underlying mechanisms leading to the occurrence of an unstable flow at the advancing flow-front during the filling of a rectangular Hele-Shaw cell. Our experimental results have revealed the existence of an elastic finger-like instability at the advancing flow-front that develops in semidilute solutions of high molecular weight polymers, with an onset time of approximately a few hundred milliseconds. Although at shear rates above critical, narrow finger patterns develop at the flow-front, their amplitude and number remain roughly constant throughout the flowing. At critical condition, no secondary flow was observed in the vicinity of the front region where the unstable flow develops. Transient response of the normal stress difference and the shear stress in the plateand- plate geometry at shear rate above critical (for the elastic fingering instability in the Hele-Shaw cell) did not reveal any anomalous that could lead to the formation of such finger-like instabilities. These instabilities were observed for both the ideal elastic Boger fluids and shear thinning viscoelastic fluids.Peer reviewed: YesNRC publication: Ye

Dynamics of linear entangled polymers reinforced with nanoscale rigid particles

Peer reviewed: YesNRC publication: Ye

Dynamics of monodisperse linear entangled polymer melts in extensional flow: the effect of excluded-volume interactions

We present an extension of the Rouse-CCR tube model for linear entangled polymers, by incorporating interchain repulsive excluded-volume interactions, to interpret extensional viscosity data of narrow molecular weight distribution polystyrene melts in strong extensional flows. The expression for the stress tensor is also adapted to account for modifications of the effective tube diameter due to flow-induced chain stretch. Despite its simplicity, the resulting model correctly captures the extensional rheological behavior of linear entangled monodisperse polystyrene melts already published in the literature.NRC publication: Ye