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
was determined.
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