| Summary: | A parameter identification issue for Hill's orthotropic model to characterize plastic and creep properties of reinforced plastics is revisited on the premise of the practical use of the numerical material testing (NMT) in decoupled multiscale analyses based on homogenization theory. Specifically, the use of optimization methods is suggested to determine the Hill's constants that represent elastic limits followed by plastic flows in anisotropic plasticity and stress-relaxation in anisotropic creep. To examine the effectiveness of the present strategy, NMTs are conducted on three separate periodic microstructures (unit cels) to obtain the macroscopic stress-strain or time-creep-strain curves and the particle swarm optimization (PSO) algorithm is employed for parameter identification. In each of the unit cells, polyamide and epoxy resins, which are assumed to respectively exhibit plastic and creep deformations, are selected for matrix phases, while carbon is taken as a reinforcing material in unidirectional-fiber, plain-weave-fiber and particulate-dispersion reinforced plastics. During the course of the examination, we also discuss the implication of the ratios of orthotropic elastic constants in the determination of Hill's constants for the creep model in terms of the relaxation spectrums in the directions of material axes.
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