Damage evaluation and strain monitoring of composite plates using metal-coated FBG sensors under quasi-static indentation

Metal-coated optical fiber sensors (MCOFSs) have a memory effect due to the elasto-plastic characteristics of the metal coating. Our study is first implementation of a new concept for damage evaluation of composite plates using the memory effect of MCOFSs. Quasi-static indentation (QSI) tests for a carbon fiber reinforced plastic (CFRP) composite plate were performed using metal-coated fiber Bragg grating (FBG) sensors. For validation of the QSI tests, a finite element analysis (FEA) based on the continuum damage mechanics (CDM) considering a damage model was performed using a commercial software, ABAQUS/Explicit. The structural responses and damage propagation of the composite plate under QSI were investigated. The results obtained by the experiments and the FEA agreed well. It was found that the metal-coated FBG sensor well monitored the strains of the plate under QSI in real-time. Moreover, the induced permanent residual strains of the surface bonded metal-coated FBG sensors increased with an increase of two parameters (i.e., the central displacement of indentor and the total energy). Based on the damage propagation of the plate and the correlation among three parameters including the residual strains, three damage levels of composite plates were classified. It was verified that the damage level of the composite plate can be simply evaluated by assessing the induced residual strains by metal-coated FBG sensors.