Co-authors​ :

 Risa TAKASHIMA (JAPAN), Ryo HIGUCHI (JAPAN), Sota OSHIMA (JAPAN), Tomohiro YOKOZEKI (JAPAN), Takahira AOKI (JAPAN) 

It is known that thermoplastic resins used as matrix materials for Carbon Fiber Reinforced Thermoplastics, which have attracted attention in recent years. Some of thermoplastic resins have semi-crystalline properties and the mechanical properties of semi-crystalline polymers have a difference between the crystalline and amorphous phases. In addition, the microstructure of them formed by the crystalline and amorphous phases changes according to molding conditions including crystallization temperature, which in turn changes the mechanical properties of thermoplastic resin itself. It has also been reported that the crystalline phase may fracture with a crack before the amorphous phase, which has a lower Young's modulus. Also, the crystalline phase has anisotropy elastic property that depends on the direction of crystal growth. Some studies to gain the machanical properties of semicrystalline polymers by numerical simulations are performed, for example the reserch about elastic finite element analysis considering the crystalline structures and elastic-plastic finite element analysis with the model assumed the microstructure. Therefore, in order to understand the more accurate mechanical properties of semi-crystalline thermoplastics through numerical analysis, in addition to reflecting the molding conditions and difference of associated microstructure, elastic-plastic finite element analysis with constitutive equations based on the deformation mechanism of each phase is necessary.
In this study, numerical simulations are performed in two stages. First, crystallization analysis using the Phase Field method is performed using two-dimensional representative volume elements to obtain the microstructure at different crystallization temperatures. Next, a nonlinear finite element analysis is performed using a　homogenized model based on the results of the crystallization simulation, with different constitutive equations for the crystalline and amorphous phases. Here, the constitutive equation is assumed to cause elastic deformation in the amorphous phase and elastic-plastic deformation in the crystalline phase. Finite element analysis with periodic boundary conditions using the key degree of freedom is used to obtain macroscopic mechanical properties. This allows us to predict the mechanical properties of thermoplastic resins considering the molding conditions. Finally, comparing the simulation result with experimentally obtained values, accuracy of this method is validated.