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Residual Stresses and Birefringence in Gas-assisted Injection Molding of Amorphous Polymers: Simulation and Experiment

Carrillo, Antonio J.
http://rave.ohiolink.edu/etdc/view?acc_num=akron1214313599

Abstract Details

2008, Doctor of Philosophy, University of Akron, Polymer Engineering.
This study presents measurements and simulations of the distribution of the birefringence components, [Delta]n and nrr-nθθ, and the average birefringence, nzz-nθθ, and polymer/gas interface in polystyrene (PS) and polycarbonate (PC) spiral-shaped tubular moldings obtained by Gas-Assisted Injection Molding (GAIM) under various processing conditions. Furthermore, free quenching experiments in cylindrical samples were carried out at different initial temperatures, and various components of birefringence and stresses were measured and simulated. The flow- and thermally-induced stresses were simulated using linear and nonlinear viscoelastic theories, respectively. The flow- and thermally-induced birefringence components were calculated using the stress-optical rule and photoviscoelastic model, respectively. The governing equations of the GAIM process were derived using a nonlinear viscoelastic model and solved using a hybrid finite element/finite difference/control volume method. The governing equations to calculate the thermally-induced stresses were discretized using finite differences. The numerical results predicted qualitatively the effect of the processing variables on the polymer/gas interface distribution of the GAIM moldings. It was found that the processing variables that strongly affected the interface distribution were the injection speed, gas-delay time, and the shot size. The processing variables that exerted less influence on the polymer/gas distribution were the gas pressure and the melt and mold temperatures. The processing variables that strongly affected the birefringence [Delta]n were the melt temperature, injection speed, and gas-delay time. The mold temperature, gas pressure and shot size exerted less influence on [Delta]n. For PS GAIM moldings the measured birefringence near to the outer wall did not relax when a section was annealed at a temperature close to the glass transition temperature while the birefringence near to the inner wall did relax significantly. This observation was consistent with the idea that the birefringence at the outer wall was mainly induced by shear and normal stresses, while that at the inner wall was induced by thermal stresses. For PC GAIM moldings the measured [Delta]n and nrr-nθθ relaxed significantly near the inner and outer walls, suggesting that the thermally-induced stresses exerted a strong influence on the birefringence throughout the wall thickness. The simulated birefringence qualitatively described the measurements. Summation of simulated thermally- and flow-induced birefringence provided a better description of measured birefringence in PS GAIM moldings. However, for PC GAIM moldings, simulations showed large discrepancies. This was attributed to the strong influence of thermally-induced birefringence throughout the wall thickness of the molding. Melt temperature, gas-delay time, and injection speed strongly affected the average birefringence in PS GAIM moldings while the shot size and gas pressure exerted less influence. For PS GAIM moldings the contribution of the thermally-induced average birefringence was minimal while for PC GAIM moldings it was significant.
Avraam Isayev, Ph. D. (Advisor)
464 p.
Polymers
Gas-assisted Injection Molding; Birefringence; Residual Stresses

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Citations

  • Carrillo, A. J. (2008). Residual Stresses and Birefringence in Gas-assisted Injection Molding of Amorphous Polymers: Simulation and Experiment [Doctoral dissertation, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1214313599

    APA Style (7th edition)

  • Carrillo, Antonio. Residual Stresses and Birefringence in Gas-assisted Injection Molding of Amorphous Polymers: Simulation and Experiment. 2008. University of Akron, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1214313599.

    MLA Style (8th edition)

  • Carrillo, Antonio. "Residual Stresses and Birefringence in Gas-assisted Injection Molding of Amorphous Polymers: Simulation and Experiment." Doctoral dissertation, University of Akron, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=akron1214313599

    Chicago Manual of Style (17th edition)

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This open access ETD is published by University of Akron and OhioLINK.