Viscoplasticity analysis of semicrystalline polymers: A multiscale approach within micromechanics framework

Abstract

The crystalline segment of semicrystalline polymers can undergo phase separation and creates distinguishable microscale crystalline and amorphous domains. In general severe mechanical and thermal loading conditions may change the amorphous, crystalline and morphological textures of these semicrystalline polymers. Due to the fact that the mechanical responses of these individual components, i.e. crystalline and amorphous polymers, are well-studied in the literature, a multiscale analysis can effectively correlate these micro-constituents properties to the macroscopic mechanical responses of the semicrystalline structures. Although the multiscale Finite Element Analysis (FEA) of the real microstructures encounters with some difficulties, such as computational costs, the micromechanics approach compensate for the FEA limitations. The micromechanics framework correlates the macroscopic mechanical responses to the microscale constitutive behaviors by either analytical or numerical methods. In this study a multiscale theory is developed within the micromechanics framework which links the microscale and macroscale constitutive behaviors of the semicrystalline polymers and also it accounts for the texture updates. While in the developed multiscale approach the crystal plasticity can effectively describe the inelastic responses of the crystalline sub-phase, a novel viscoplastic constitutive relation for the amorphous glassy polymers is developed to enhance the performance of the multiscale approach. The proposed amorphous viscoplastic model minimizes the numbers of material parameters, and it significantly facilitates the calibration process. Also the developed constitutive relations for the amorphous polymers provide the mathematical competency to capture a wide range of experimental results. A reformation of the Transformation Field Analysis (TFA), developed by Dvorak (1990, 1992) and Dvorak and Benveniste (1992), is then presented where the two-phase TFA solution is generalized for capturing local inelastic responses of semicrystalline polymers. Its performance is then examined for the case of finite deformation kinematics. Also the reported TFA deficiency in overestimating the inelastic responses, e.g. Chaboche et al. (2001), is addressed herein in which the elasto-plastic stiffness together with some phenomenological material parameters are incorporated into the TFA formulation to soften its mechanical responses. The multiscale approach and the proposed viscoplastic model provide good correlation with the experimental results.