Investigation of Creep Behavior of L‐Shaped Composite Components Under Curing Residual Stresses Using Embedded Fiber Bragg Gratings

ABSTRACT L‐shaped composite components are widely used in aerospace structures. These components not only spring‐in due to residual stress release after demolding, but also exhibit long‐term creep. However, the effects of the layup, thickness, and R‐region angle of L‐shaped structures on the creep strain remain unclear. In this study, L‐shaped Carbon fiber reinforced polymer (CFRP) specimens with different R‐region configurations were designed, and fiber Bragg grating (FBG) sensors were embedded at 1/8, 1/2, and 7/8 of the R‐region thickness for 21‐day monitoring. Creep strain curves were reconstructed from FBG wavelength data and validated by laser displacement and obliquely bonded FBG measurements. The strain difference between the upper and lower layers decreases significantly after demolding, indicating partial residual stress release and spring‐in, while subsequent creep produced continuous spring‐back. Creep strain increased rapidly within the first 100 h and stabilized after about 400 h. The average creep strain increased with the proportion of 90° plies but decreased with increasing thickness and R‐region angle. At 750 h, the ratio of creep‐induced spring‐back to demolding‐induced spring‐in depended on layup rather than thickness or R‐region angle, reaching about 17.28% for orthogonal layups. Under the same material system and curing conditions, structural parameters therefore primarily affect the magnitude of creep deformation, but affect little on creep stabilization time. These results provide a basis for forming‐angle prediction and dimensional‐stability evaluation of L‐shaped composite components.