Inverse Calibration of Constituent Mechanical Properties in GFRP Using the Serial/Parallel Mixing Theory and FEM with Validation via Three-Point Bending Test

This study proposes a systematic inverse characterization framework for identifying the elastic properties and damage-related constitutive parameters of Glass Fiber Reinforced Polymer (GFRP) laminates within a unified micromechanical–finite element formulation. A reduced yet physically targeted experimental campaign—including longitudinal and transverse tension, compression, shear, and three-point bending tests—is conducted to enable a hierarchical calibration of fiber and matrix parameters. The identified constituent properties are implemented within a three-dimensional finite element model based on the Serial/Parallel Mixing Theory (SPMT) coupled with an isotropic damage formulation at the constituent level. Unlike conventional approaches that assume elastic properties from literature and calibrate only damage-related parameters, the proposed methodology extends inverse identification to the elastic regime, enhancing physical consistency and reducing parameter uncertainty. Independent validation is performed through three-point bending tests without additional parameter adjustment. The model accurately reproduces both the global force–displacement response and the equivalent stress–strain behavior in the initial elastic regime and the subsequent damage-driven nonlinear regime, demonstrating strong predictive capability under flexure-dominated loading. Overall, the proposed framework provides a robust and physically grounded strategy for improving the reliability and transferability of micromechanical composite models while minimizing experimental effort.