I made a lecture in a workshop on computational techniques for polymer processing held at Kyoto Institute of Technology on Sep. 30, 2016. The lecture was owing to the invitation by Prof. Nishimura and Prof. Togawa in KIT, and the title was multi-scale simulations for polymer processing. The word “multi-scale” here means that the simulations were made in combination of two different levels of descriptions. One of the calculations was made in a molecular level in which the material properties (i.e., the rheology in this particular case) were predicted from the molecular structure. The other calculation was a continuum level calculation in which the material flow behavior was predicted on the basis of the material parameters obtained from the molecular calculation.
The figure above shows one of the examples of the multi-scale calculation. Here, I attempted to simulate warpage of injection molded product made of two different polymers with different molecular weights. For the short molecule, the relaxation time is short and the molecules are not that stretched in the final product. Then the warpage is dominated by the thermal expansion coefficients. On the other hand, for the long molecule, due to its long relaxation time, the molecular stretch remains in the product, and thus, the residual stress induces the warpage in the opposite direction to the case for the short molecule.
Because most of the audience in the lecture hall were not that familiar with the molecular things, I spent 60% of my talk to convey the importance of molecular insight of polymer processing. I was happy to see that nobody got sleep in the room, even though my talk was just after lunch ;->
I appreciate the kind invitation of the professors and the kind attention of the audience.