Coupled nano-interfacial and agglomeration effects on elastic behavior of hybrid composites using multi-scale modeling

In this work, a novel multi-scale micromechanical model is developed to effectively predict the overall elastic properties of nano-coated carbon fiber reinforced hybrid composites (NCRHC). The present model investigates the impact of CNT-matrix interfacial shells and CNT agglomeration on the characteristics of NCRHC using a novel mean-field theory (MFT) coupled with a 3D mechanics of material (MOM) micromechanics approach. The mean-field theory is employed to analyze the nonlinear behavior of the elastic properties in the agglomerated nano-coated region (NCR). Most of the existing mathematical models neglect the nonlinear behavior of elastic properties due to the interfacial shell and fail to capture the weakening effects of high nanofiber (CNT) concentrations, which contradicts experimental observations. This discrepancy is overcome by incorporating an empirical relation for the interfacial shell, emphasizing the critical role of CNT-matrix interactions and agglomeration in enhancing the effective properties of the NCR region and the overall stiffness of NCRHC. To demonstrate the accuracy and applicability of the present approach, the prediction from the MFT model is validated with experimental results of two-phase nanocomposite while the multi-scale analysis results are compared with available experimental results for three-phase NCRHC, showing strong agreement. Subsequently, the effect of CNT aspect ratio, agglomeration parameters, interfacial shell properties, and matrix modulus on the effective stiffness of NCRHC are thoroughly examined. The study also highlights optimal CNT fiber concentrations that improve the effective properties of the three-phase hybrid composite, while mitigating the detrimental effects of agglomeration and interfacial issues.