Surface strain measurements on carbon fiber-reinforced polymer (CFRP) structures using bonded strain gauges are often systematically underestimated due to strain transfer effects associated with the surface resin-rich layer. To investigate this issue, comparative bending experiments were performed on steel and CFRP beams, where the steel beam served as a reference structure with negligible strain transfer loss under equal-curvature conditions. An equal-curvature bending framework was established to ensure identical bending curvature at the strain measurement location for both materials, thereby eliminating the influence of material stiffness on global deformation. In parallel, controlled surface polishing was employed to precisely regulate the thickness of the resin-rich layer on CFRP specimens, enabling systematic evaluation of its influence on strain transfer behavior. Experimental results under equal-curvature conditions reveal a stable strain underestimation in CFRP surface measurements, with an average strain transfer coefficient of approximately 0.968. Furthermore, reducing the resin-rich layer thickness leads to a consistent increase in measured strain. Based on these observations, a practical strain correction model was established to improve the reliability and engineering applicability of surface strain measurements in CFRP structures.
Xue et al. (Mon,) studied this question.