The basic technologies of the impact damage detection system (IDDS) of composite structures were developed and
demonstrated using a composite structure with embedded small-diameter optical fiber sensors by Authors in FY2002. In
our current R&D, the IDDS consisting of composite structure with embedded optical fiber sensors and interrogation
units is developed for practical airframe application. The system evaluation by using composite substructures and coupon
specimens are planned to proceed towards product. As one of the foremost tasks for the application, it is important to
evaluate the system whether having the probability of damage detection sufficiently or not. In this study, to evaluate the
probability of detection of the system, the impact tests for barely visible impact damage (BVID) are conducted by using
coupon specimens with being embedded small-diameter optical fibers. From the test result, reliability of the IDDS is
evaluated.
We are now developing an impact damage detection (IDD) system for composite airframe structures. The basic
technologies of IDD system were developed and demonstrated using a composite structure with embedded small-diameter
optical fiber sensors by Authors in FY2002. IDD system consists of a composite structure with installed optical
fiber sensors and a monitoring measurement system. To get the prospect of aircraft application of IDD system is a target
of this development. To investigate the durability of embedded optical fibers and composites, cyclic loading test is
conducted using composite coupon specimens with embedded small-diameter optical fibers. The evaluation of the
system by using composite substructures is also conducted to proceed towards product. This paper presents the
development target, our technology, test method, test result and future task.
It is well known that barely visible damage is often induced in composite structures subjected to out-of plane impact, and the mechanical properties of the composites decrease markedly. In this study, some element technologies for the detection of the damage are explained. Those are (1) the technologies for the arrangement of embedded small-diameter optical fibers which have no serious effect on the mechanical properties of composites, (2) the technologies for the egress of the optical fibers using “the embedded connector for smart structures” which can be trimmed without care about the optical fibers, (3) the technologies for the damage detection system that has the functions for data acquisition and analysis, the evaluation of the initiation and the position of damage, and the visualization of damage information. The impact test using the composite airframe demonstrator is conducted. The sensors embedded in the upper panel of the stiffened cylindrical composite structure with 1.5 m in diameter and 3 m in length, are FBG sensors for strain measurement and the optical fibers for optical loss measurement. The detection of damage in the composite structures using a developed damage detection system is demonstrated.
It is well known that barely visible damage is often induced in composite structures subjected to our-of-plane impact, and the mechanical properties of the composites decrease markedly. So far, for the significance of the damage monitoring, the impact test of the CFRP laminate plates with embedded small-diameter optical fibers were conducted, and it was found possible to detect impact load and impact damage in real-time by measuring the optical loss and strain response. But the stiffened composite panels, which are the representative structural elements of airplane. Are characterized by different impact damage from that of the composite plates. In this study, single-mode and multi-mode optical fibers are used as a sensor for detecting impact load and impact damage in curved/stiffened composite panels. Those fibers have polyimide coating and about 40 micron in diameter which will have no serious effect on the mechanical properties of composites. Impact test are performed using the panels with wavy embedded optical fibers. The characteristics of impact damage are investigated. The impact load, the strain measured by FBG sensors and the optical intensity of the optical fibers embedded in the composites are monitored as a function of time. And we discuss the relationship between optical response, impact load and impact damage.
It is well known that barely visible damage is often induced in composite structures subjected to out-of plane impact, and the mechanical properties of the composites decrease markedly. The stiffened composite panels, which are the representative structural elements of airplane, are characterized by different impact damage from that of the coupon level specimens. Therefore, the goal of this study is that small-diameter optical fiber sensors are applied in stiffened composite panels, and it is discussed about the possibility of the detection of impact damage in the structures by the sensors. In this study, both multi-mode optical fibers and fiber bragg grating (FBG) sensors are used for detecting impact load and impact damage in stiffened composite panels. The fibers have polyimide coating and about 40 micrometers in cladding diameter which will have no serious effect on mechanical properties of composites. Impact tests are performed using the stiffened composite panels with embedded optical fibers. The characteristics of impact damage are investigated. The impact load, the strain and the optical responses of the optical fibers are measured as a function of time. And we discuss the relationship among the optical responses, the impact load and the impact damage.
It is well known that the compression after impact (CAI) strength of carbon fiber reinforced plastic (CFRP) laminates decreases by impact damage, especially delamination. The impact damage has a close relation to impact energy, which can be derived from the time history of impact load. Thus, it is important to detect the impact load applied to the composites. In this study, single-mode or multi-mode small-diameter optical fibers embedded in CFRP laminates were used as a sensor for detecting the impact load. Diameters of the cladding and the polyimide coating are 40 μm and 52 μm, respectively. Such optical fibers embedded inside laminas cause no serious effect on the mechanical properties of composites. The optical fiber sensors were able to detect the impact by bending loss in the vicinity of impact point. The optical fibers were embedded parallel to reinforcing fibers in CFRP composites. Charpy impact tests were performed for the CFRP specimens. The strain on the surface of the specimens, the optical loss and the impact load were measured as a function of time. Then, the relationship between the optical loss and the impact load was discussed experimentally and theoretically.
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