Mechanical behavior of unidirectional fiber reinforced polymer based on micromechanical model

Although macroscopic finite-element simulations based on classical composite failure criteria such as Hashin’s can account for macroscopic damage mechanisms such as fiber fracture, matrix damage, and delamination, these approaches are unable to represent microscopic damage mechanisms within carbon-fiber-reinforced polymer (CFRP), particularly interfacial debonding between fibers and the matrix. To overcome this limitation, a multiphase micromechanical model was developed that explicitly incorporates distinct constituent phases-fiber, matrix, and interface. This model integrates multiple damage mechanisms such as fiber fracture, matrix failure, and interfacial debonding, enabling a more granular analysis of damage initiation and progression. Periodic boundary conditions were applied to the model to ensure kinematic consistency and mechanical representativeness. A mesh-convergence study was subsequently carried out on the basis of the predicted elastic moduli of CFRP in various material directions, leading to an optimized discretization strategy that balances accuracy and computational cost. Comprehensive validation was performed by comparing the model-predicted stress-strain responses with experimental data obtained from unidirectional CFRP (UD CFRP) under a range of loading conditions, including transverse tension and compression, longitudinal tension and compression, and in-plane and out-of-plane shear. The damage-evolution processes under these representative loading paths were systematically analyzed. The results indicate that the relative errors in peak stress and failure strain between simulations and experiments are less than 5%. Moreover, the crack-propagation paths predicted by the model show strong agreement with observations from scanning electron microscopy, thereby confirming the accuracy of the proposed microstructure-aware micromechanical modeling framework. Furthermore, the model successfully captures the detailed damage evolution of UD CFRP under various loading scenarios. Under transverse tensile loading, damage is initiated by interfacial debonding, followed by plastic deformation and eventual failure of the matrix near debonded regions. In contrast, under transverse compression, interfacial debonding and matrix plastic deformation are observed to occur simultaneously. Under longitudinal loading, the dominant damage mechanism is identified as fiber fracture, whereas the damage patterns under in-plane and out-of-plane shear are found to be consistent with those under transverse compression and transverse tension, respectively. These insights offer significant engineering value for the development of damage-tolerant design criteria and structural-integrity evaluation frameworks for CFRP components and assemblies.