Structural Health Monitoring of CFRP Sandwich Structures by Optical Fiber Based Distributed Strain Measurement

摘要

Since composite facesheets are very thin and lightweight core is weak, composite sandwich structures can be easily damaged wiien impact or indentation load is applied. The core under loading point crushes and a dent of the facesheet remains. The dent significantly deteriorates the stiffness and strength of the sandwich structures, even when it is small and barely visible. In this study, an impact damage detection system for large sandwich structures is established by using a specific response of pre-pump pulse Brillouin optical time domain analysis (PPP-BOTDA) sensing system. This system employs stimulated Brillouin scattering in an optical fiber and realizes distributed strain measurement with spatial resolution of 10 cm, sampling interval of 5 cm and sensing range of 1 km. A Brillouin gain spectrum (BGS) becomes broader corresponding to the strain gradient along the optical fiber. In the damage detection system, the specific response is employed to detect non-uniform strain distribution along the dent of the facesheet. A validity of the proposed damage detection system is confirmed through an indentation damage detection test.