Rheological measurement of the nonlinear viscoelasticity of the ABS polymer and numerical simulation of thermoforming process

Abstract

The thickness distribution of thermoformed products is greatly affected by the viscoelastic behavior of the extruded polymer sheet. In this work, linear and nonlinear rheological experiments are carried out to characterize the viscoelastic properties of acrylonitrile-butadiene-styrene sheets under thermoforming conditions including a wide range of temperatures, strains, and strain rates. First, aspects of linear viscoelasticity such as the storage modulus and loss modulus are measured by small-amplitude oscillatory shear experiments. The discrete relaxation spectra and the Williams-Landel-Ferry parameters are obtained from the constructed linear master curves. Then, nonlinear time-dependent extensional viscosity is measured by uniaxial extensional experiments. The parameters of the damping function are evaluated using an optimization method. In addition, the effect of the orientation of the polymer is analyzed. The uniaxial extensional stress and viscosity in the extruder direction demonstrate higher resistance against tearing and extreme thickness reduction during processing. Finally, the linear and nonlinear input parameters for the numerical simulation are prepared. Numerical simulations are performed using the Wagner model with the obtained nonlinear viscoelasticity. The thickness distribution in thermoformed ABS sheets, obtained numerically, shows good agreement with the experimentally obtained values.

Thermoformability analysis of TPO sheets blended with postindustrial secondary feedstock

“…Storage modulus as a function of temperature [14,15] Rheological testing Melt strength, elongational viscosity [7,[16][17][18][19][20][21] Tensile testing Elastic modulus, elongation at break, load at yield [7] Areal draw ratio DR area ð Þ: DR area ¼ Formed part of surface area Sheet surface area :…”

Polymer-tool friction coefficient in temperature for thermoforming numerical simulation

“…To describe this particular behavior, T-SIM use the K-BKZ type viscoelastic Wagner Model. This model shows good results for the simulation of the thermoforming process for ABS [2,4], PS [14], or HDPE [15]. The Wagner model is expressed as follows (3):…”

“…However, for manufacturers, a uniform thickness distribution and a high average thickness are very important parameters for the manufacture of high-quality parts. This thickness distribution is mainly affected by the viscoelastic behavior of the extruded polymer sheet [2,3,4] but previous work show that contact friction also has a huge impact on thickness distribution [2,[5][6][7][8]. In the literature, the majority of authors study the effect of friction in the context of plug assist thermoforming.…”

3D Printed Sand Tools for Thermoforming Applications of Carbon Fiber Reinforced Composites—A Perspective

“…As a remedy, a pre-stretching step may be introduced after the heating step. In that case a clamping tool fixes the edges of the sheet and air pressure is applied to inflate the sheet into a bubble ( Figure 2 b) [ 26 ]. In the next step, forming is achieved by vacuum pressure.…”