This study presents a unified multi-scale fatigue damage modeling approach for carbon fiber reinforced epoxy composites, implemented in Abaqus through a UMAT subroutine. Fiber and matrix dominated failure modes are described by the 3D Hashin criteria, while the subsequent coupled degradation of stiffness and strength is modeled using the Shokrieh–Lessard approach. Furthermore, Khan's modification is incorporated into the fatigue-life formulation to normalize the life parameter by transverse strength, thereby improving the representation of transverse fatigue behavior. Mori–Tanaka mean-field homogenization is used to update the effective ply moduli on a cycle-by-cycle basis. By integrating directly with the finite‐element solver, the framework captures damage initiation, stiffness degradation, and the ensuing evolution of residual strength under fatigue loading. The results show that the predicted fatigue lives are consistent with experimental data for carbon/epoxy unidirectional (UD) laminates. The proposed framework provides a practical computational approach for predicting the fatigue life of composite materials.

Keywords: Fatigue, Multi-scale, CFRP, Micromechanics