Hideyuki Hara

Development of simulation technology for production of porous polymeric membranes

Porous polymeric membranes are used for ion exchange membranes, membrane filter and separators of batteries owing to its micro-porous structure. Extension method is one of the inexpensive processes of such membrane. However, any suitable stability condition of the process has not yet been clarified. In this study, SEM (Scanning Electron Microscope) observations in production process are carried out and the simulation technology for production is developed for improvement in productivity. In this simulation model, the evolution equation of microscopic damage, constitutive equation depending on microscopic damage and the homogenization method are used for representation of evolution of micro-porous structure of crystalline polymer. It is indicated that numerical results obtained here are in good agreement with the SEM observations.

Three-Dimensional FE Analysis Using Homogenization Method for Ductile Polymers Based on Molecular Chain Plasticity Model Considering Craze Evolution

Thermoplastic polymers can be classified into glassy polymers and crystalline polymers depending on their internal structures. Glassy polymers have a random coil structure in which molecular chains are irregularly entangled. Crystalline polymers can be regarded as a mixture consisting of glassy and crystalline phases where molecular chains are regularly folded. Moreover, the fracture of ductile polymers occurs at the boundary between regions with oriented and non-oriented molecular chains after neck propagation. This behavior stems from the concentration of craze, which is a type of microscopic damage typically observed in polymers. In this study, three-dimensional FE simulations coupled with a craze evolution equation are carried out for glassy and crystalline polymers using a homogenization method and models of ductile polymers based on crystal plasticity theory. We attempt to numerically represent the propagation of a high-strain-rate shear band and a high-craze-density region in the macroscopic structure and to directly visualize the orientation of molecular chains in glassy and crystalline phases. In addition, differences between the deformation behavior of glassy and crystalline polymers at both the macroscopic and microscopic scales are investigated.

Fracture Prediction Simulation for Crystalline Polymer Using Homogenized Molecular Chain Plasticity and Craze Evolution Models

The fracture of ductile polymers occurs on the boundary between the molecular chain-oriented and non-oriented regions after the neck propagation. This behavior is caused by the concentration of craze that is a microscopic damage typically observed in polymers. In addition, it is known that the ductility of polymers decreases both at a high and a low strain rates in comparison with that at a middle one. In this paper, FE simulations are carried out for a crystalline polymer subjected to the tensile load at some strain rates by use of a homogenized molecular chain plasticity model and a craze evolution equation based on the chemical kinetics. Furthermore, failure criteria are proposed from an experiment on fibril strength. A fracture prediction based on the craze accumulation and the failure of fibrils is demonstrated applying the criteria to the numerical results. It is indicated that the fracture occurs at a smaller strain under a high and a low strain rate conditions than under a middle one.