A Study on Damage Behavior and Residual Strength of Steel/ <scp>CF</scp> Hybrids Subjected to Bending and Reverse Bending Deformation

ABSTRACT Steel/carbon fiber (CF) hybrid laminates offer promise for lightweight automotive structures; however, although a previous study demonstrates that roll forming is a viable manufacturing route, bending‐induced damage to composite layers remains a critical concern affecting structural integrity in service. This study proposes a novel pure bending/reverse bending test to investigate the influence of pre‐damage on the residual mechanical performance of Steel/CF hybrids. The effects of layup configuration, pre‐bending severity, and loading path were systematically analyzed through combined experimental testing and finite element simulation. A three‐dimensional hybrid damage model incorporating an interactive damage evolution law (IDEL) was developed to capture post‐damage behavior under load reversal. Results reveal that residual strength and stiffness decrease with increasing pre‐damage severity and are strongly dependent on fiber orientation. In 0° and mixed layups, fiber buckling and interlaminar shear dominate damage progression, while in 90° layups, the response is governed by the steel substrate's kinematic hardening. The proposed model accurately captures the damage evolution and strength retention, offering new insights into the interplay between forming‐induced damage and structural integrity. This work establishes a method for evaluating the post‐forming performance of hybrid laminates, providing essential guidance for designing and forming next‐generation lightweight vehicle components.