Compressive Flow of Viscoelastic Materials.
DELAWARE UNIV NEWARK CENTER FOR COMPOSITE MATERIALS
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The compressive flow of viscoelastic materials between two parallel flat disks under a constant load has been investigated analytically, numerically, and experimentally. This process simulates a number of compression molding and lubrication experiments the purpose of our study was to assess the effects of fluid viscoelasticity and of temperature gradients in these applications. A dimensionless group has been found very useful for determining the flow regimes when there exists a substantial transverse viscosity gradient in the fluid charge, such as in the nonisothermal compression molding processes. Compressive flow of linear viscoelastic materials has been analyzed analytically. It shows that the squeezing motion becomes oscillatory when the ratio of the Deborah number to the Reynolds number is larger than a critical value, and that the linear viscoelastic materials are squeezed faster than the corresponding Newtonian cases. Compressive flow of various non-linear model fluids has also been analyzed numerically. The Maxwell fluid behaves much like linear viscoelastic materials, except under extraordinarily high loading conditions. But, the Johnson-Segalman model and the Marrucci structural model show that slower squeezing may arise after the initial rapid transient under moderate loading conditions. This slower squeezing must be due to the special features of these models, which the Maxwell model does not exhibit, such as stress overshoot in the transient flows. Experimentally two different observations have been made. A silicone polymer shows the oscillatory and the faster squeezing, which is predictable by the Maxwell type of model fluid. MM
- Lubricants and Hydraulic Fluids
- Hydraulic and Pneumatic Equipment
- Manufacturing and Industrial Engineering and Control of Production Systems
- Fluid Mechanics