This study investigated residual strain interactions in Fiber Metal Laminates (FML) made from metal and fiber-reinforced plastic (FRP) layers, focusing on CFRP-steel hybrids, using integrated Fiber Bragg Grating (FBG) sensors and X-Ray Diffraction (XRD). Understanding residual strains in such hybrids is crucial for evaluating their strength under thermal stresses during the manufacturing process of such hybrid laminates.

Two specimen types were analyzed: the C-Type, designed for tensile load testing, demonstrated linear micro- and macromechanical strain behavior, with compressive residual strains, caused by the manufacturing process and measured by FBG sensors. The HYB-Type specimens, designed to assess thermal mismatch strains, were modeled with Classical Laminate Theory (CLT), predicting a strain-free temperature range of 80°C to 100°C. 

Experimental XRD measurements identified a strain-free temperature of 88.74°C in the steel component, closely matching model predictions. Using this strain-free temperature as a reference, FBG measurements were adjusted to align with XRD results. While calculated and measured strains showed good correlation in the steel component, CFRP measurements deviated by 10.20% from theoretical values, indicating a need for refined models to account for CFRP’s anisotropic behavior. These findings underscore the importance of precise modeling and calibration for optimizing FML structural integrity.