Determination of the maximum strains experienced by composite structures using metal coated optical fiber sensors

A determination technique for the maximum strains experienced by composites is proposed using the permanent deformation characteristics of elasto-plastic metal-coated optical fiber sensors (OFSs). In order to confirm their feasibility, both analytical and experimental approaches were undertaken. In the analysis, a theoretical model for a surface-mounted OFS on the composite was proposed, and the strain transfer relations were derived. Moreover, novel numerical methods were implemented in order to evaluate the residual strain distribution. The analytical results were validated through a finite element analysis (FEA) using the ABAQUS software. We found that the residual strain increases as the coating thickness and external strain increase. In addition, the required gauge length for the given bonding length of the OFSs is proposed. In the experiment, fiber Bragg grating (FBG) sensors were applied to carbon fiber reinforced polymer (CFRP) composite specimens in order to verify the proposed technique. The trends of the residual strain, which are corresponding to the maximum strains experienced by the composite specimens, were consistent with those obtained in the analysis.