Detection of impact damage of stiffened composite panels using embedded small-diameteroptical fibers

Abstract

It is well known that barely visible damage is often induced in composite structuressubjected to out-of-plane impact, and the mechanical properties of the compositesdegrade markedly. The stiffened composite panels which are the representativestructural elements of airplanes are characterized by impact damage differentfrom that of coupon-level specimens. Therefore, the objective of this study is toapply small-diameter optical fiber sensors to stiffened composite panels for thedetection of impact damage. In this study, both multi-mode optical fibers andfiber Bragg grating (FBG) sensors are used for detecting impact load and impactdamage in stiffened composite panels. The fibers have polyimide coating with40 µm cladding diameter which has no serious effect on the mechanical properties of composites.Impact tests are performed using stiffened composite panels with embedded optical fibers.The characteristics of impact damage are investigated. The impact load, the strain and theoptical responses of the optical fibers are measured as a function of time. And we discussthe relationships among the optical responses, the impact load and the impact damage.