Seishiro Matsubara

Applicability of micro–macro decoupling scheme to two-scale analysis of fiber-reinforced plastics

The numerical study is made to demonstrate the applicability of the method of decoupling multi-scale analysis to the micro–macro evaluation of the mechanical behavior of fiber-reinforced plastics (FRP) that exhibits inelastic deformations and internal damage of the matrix material. During the course of this demonstration, it is confirmed that the reliability of the decoupling method can be guaranteed if the macroscopic constitutive model is introduced so as to inherit the microscopic material behavior. To this end, with reference to the results of the numerical material testing on the periodic microstructures of FRP, we propose an anisotropic elastoplastic-creep-damage combined constitutive model to represent the macroscopic material behavior and illustrate the characteristics of the inelastic deformations that resemble the material behavior assumed for plastics at micro-scale. With the identified macroscopic material parameters, the macroscopic structural analysis, which is followed by the localization analysis consistently, can be an actual proof of the utility value of the decoupling method in practice.

A Viscoelastic-Viscoplastic Combined Constitutive Model for Thermoplastic Resins

A viscoelastic-viscoplastic combined constitutive model is presented to represent large deformations of amorphous thermoplastic resins. The model is endowed with viscoelastic and viscoplastic rheology elements connected in series. The standard generalized Maxwell model is used to determine the stress and characterize the viscoelastic material behavior at small or moderate strain regime. To realize the transient creep deformations along with kinematic hardening due to frictional resistance and orientation of molecular chains, a proven finite strain viscoplastic model is employed. After identifying the material parameters with reference to experimental data, we verify and demonstrate the fundamental performances of the proposed model in reproducing typical material behavior of resin.