Life cycle health monitoring technology for composite airframe structures based on strain mapping is proposed. It
detects damages and deformation harmful to the structures by strain mapping using fiber Bragg grating (FBG) sensors
through their life cycles including the stages of molding, machining, assembling, operation, and maintenance. In this
paper, we firstly carried out a strain monitoring test of CFRP mock-up structure through the life cycle including the stage
of molding, machining, assembling, and operation. The experimental result confirms that the strain which arises in each
life cycle stage can be measured by FBG sensors embedded in molding stage and demonstrates the feasibility of life
cycle structural health monitoring by using FBG sensors. Secondly, we conducted the strain monitoring test of CFRP
scarf-repaired specimen subject to fatigue load. FBG sensors were embedded in the scarf-repaired part of the specimen
and their reflection spectra were measured in uni-axial cyclic load test. Strain changes were compared with the pulse
thermographic inspection. As a result, strain measured by FBG sensors changed sensitively with debonded area of repair
patch, which demonstrates that the debondings of repair patches in scarf-repaired composites due to fatigue load can be
detected by FBG sensors.
This paper proposes structural health monitoring technology based on the strain mapping of composite airframe
structures through their life cycles by FBG sensors. We carried out operational load tests of small-sized mockup
specimens of CFRP pressure bulkhead and measured the strain by FBG sensors. In addition, we confirmed strain change
due to stiffener debondings. Moreover, debonding detectability of FBG sensors were investigated through the strain
monitoring test of CFRP skin-stiffener panel specimens. As a result, the strain distribution varied with damage
configurations. Moreover, the change in strain distribution measured by FBG sensors agrees well with numerical
simulation. These results demonstrate that FBG sensors can detect stiffener debondings with the dimension of 5mm in
composite airframe structures.
The objective of this work is to develop a system for monitoring the structural integrity of composite airframe structures by
strain mapping over the entire lifecycle of the structure. Specifically, we use fiber Bragg grating sensors to measure strain
in a pressure bulkhead made of carbon fiber reinforced plastics (CFRPs) through a sequence of lifecycle stages (molding,
machining, assembly, operation and maintenance) and detect the damage, defects, and deformation that occurs at each stage
from the obtained strain distributions. In previous work, we have evaluated strain monitoring at each step in the FRP
molding and machining stages of the lifecycle. In the work reported here, we evaluate the monitoring of the changes in
strain that occur at the time of bolt fastening during assembly. The results show that the FBG sensors can detect the
changes in strain that occur when a load is applied to the structure during correction of thermal deformation or when there
is an offset in the hole position when structures are bolted together. We also conducted experiments to evaluate the
detection of damage and deformation modes that occur in the pressure bulkhead during operation. Those results show that
the FBG sensors detect the characteristic changes in strain for each mode.
The purpose of this research is to develop the structural health monitoring system for composite airframe structures by
strain mapping through their life cycles. We apply FBG sensor networks to CFRP pressure bulkheads and monitor the
strain through their life cycles: molding, processing, assembly, operation and maintenance. Damages, defects and
deformations which occurred in each stage are detected using the strain distribution. At first, we monitored the strain of
CFRP laminates during molding and processing with FBG sensors. As a result, not only the thermal strain on curing
process but also strain change due to demolding was measured precisely. In addition, we analyzed the change in strain
distribution due to damages of CFRP pressure bulkhead such as stringer debonding and impact damage of skin under
operational load in flight. On the basis of these results, the location of FBG sensors suitable for the detection of damages
There is a growing demand in recent years for lightweight structures in aircraft systems from the viewpoints of energy
and cost savings. The authors have continued development of the Highly Reliable Advanced Grid Structure (HRAGS)
for aircraft structure. HRAGS is provided with health monitoring functions that make use of Fiber Bragg Grating (FBG)
sensors in advanced grid structures. To apply HRAGS technology to aircraft structures, a full-scale demonstrator
visualizing the actual aircraft structure needs to be built and evaluated so that the effectiveness of the technology can be
validated. So the authors selected the wing tip as the candidate structural member and proceeded to design and build a
demonstrator. A box-structure was adopted as the structure for the wing-tip demonstrator, and HRAGS panels were used
as the skin panels on the upper and lower surfaces of the structure. The demonstrator was designed using about 600 FBG
sensors using a panel size of 1 x 2 m. By using the demonstrator, damage detection functions of HRAGS system were
verified analytically. The results of the design and evaluation of the demonstrator are reported here.
There is a growing demand for lightweight structures in aircraft systems for energy and cost savings. The authors have
therefore continued development of the Highly Reliable Advanced Grid Structure (HRAGS) with the aim of application
of the same to aircraft. HRAGS is provided with health monitoring functions that make use of Fiber Bragg Grating
(FBG) sensors in advanced grid structures, which have been the focus of attention in recent years as lightweight
structures. It is a new lightweight structural concept that enables lighter weight to be obtained while maintaining high
This report describes the tests and evaluation of the Proto System conducted to verify experimentally the concept of the
highly reliable advanced grid structure. The Proto System consists of a skin panel embedded with 29 FBG sensors and a
wavelength detection system. The artificial damage to the skin panel of the specimen was successfully detected by
comparing the strain distributions before and after the introduction of the damage measured by FBG sensors. Next, the
application of HRAGS to the wing tip was studied. The results of the studies above are reported here.
There is a growing demand for lightweight structures in aircraft systems for realizing energy and cost savings. The authors are developing a new lightweight grid structure for aircraft applications equipped with a health monitoring system utilizing fiber Bragg grating (FBG) sensors. The grid structure has a very simple path for stress, which is easily detected by FBG sensors embedded in the ribs. In this research, the difference in the strain distributions before and after damage to the grid structure was evaluated analytically, and a damage detection method was established. The correspondence between damage detection ability and damage tolerance design strength was clarified. Furthermore, the damage tolerance design method was established based on the evaluation of residual strength corresponding to the detected damage level of rib. Next, the prototype of a highly reliable grid structure embedded with FBG sensors was manufactured, and the damage detection ability was experimentally verified. The panel size of the specimen was 525 x 550 mm and 29 FBG sensors were embedded at the center of the panel. Load was applied on the grid panel, and the strain distribution was measured by the multipoint FBG sensors. The artificial damage introduced in one rib of the specimen and the position of the damage, were successfully detected by comparing the strain distributions before and after the introduction of the damage.
Grid structures are the structures made of the trusses consisting of simple ribs. Especially, the structure which uses carbon fiber reinforced plastic (CFRP) unidirectional composites as ribs is called advanced grid structures (AGS). Highly Reliable Advanced Grid Structure (HRAGS) is one of the AGS in which fiber Bragg grating (FBG) sensors are embedded in the longitudinal direction of the ribs in order to detect various damages that appear in the composite grid structures. In this research, the authors tried to identify the damage location in AGS from the structural strain distribution measured by FBG sensors embedded in all ribs. When some damages appear in the AGS, the structural strain distribution in the AGS changes accordingly. Considering the tendency of change, the damage location was identified. At first, FBG sensors were embedded into AGS and three point bending test was examined. The result showed that these embedded sensors could detect the strains applied to the corresponding ribs. Then, low velocity impact test was carried out, which revealed that only fiber breakage was appeared in the AGS. Moreover, three types of models for finite element analysis (FEA) were proposed and compared with the experimental result. According to the comparison, the authors selected beam element model (BEM) for damage-location identification in this research. Furthermore, strain distributions in the structure including damages were calculated with this model. The result proved that the identification of damage location could be realized.
The authors have been developing a new lightweight composite grid structure equipped with a health monitoring system utilizing FBG (Fiber Bragg Grating) sensors for aircraft applications. A grid structure, comprising multiple interconnected ribs in a truss-like arrangement, has a very simple path of stress, which is easily detected with FBG sensors embedded in the ribs.
In this study, manufacturing technology for embedding optical fibers into the grid structure was studied, in order to enable an embedded multi-point FBG sensor network. A total of 29 FBG sensors were embedded in a 525 x 550 mm test panel. A third test panel was also fabricated to evaluate effect of steering the optical fiber through the grid panel nodes. The strain data obtained from embedded FBG sensors were compared to ones from conventional strain gages in several loading conditions, which showed very good accordance. An appropriate arrangement of the grating wavelength of the embedded FBG sensors was also studied to show the feasibility a new lightweight composite grid structure with an excellent health monitoring system.
Future large aperture telescope projects will require very lightweight mirrors that can be produced at significantly lower cost and faster production times than currently possible. Tailorable, low thermal expansion composite materials offer an attractive path to achieve these goals. Application of carbon/carbon composites is particularly attractive as these materials do not exhibit the moisture-absorption-related expansion problems observed in typical resin matrix composites. The National Astronomical Observatory of Japan and Mitsubishi Electric Corporation are collaborating to develop materials and surface finishing technologies to enable future carbon/carbon composite mirror applications. Material processing techniques for improved substrate surface finish have been developed. An innovative surface finish approach involving high precision machining of a metal layer applied to the mirror surface has also been developed. As a result, 150mm diameter C/C spherical mirror with honeycomb sandwich structure was successfully demonstrated.