CFRP (Carbon Fiber Reinforced Plastics) is the ideal material for space based mirror due to its low thermal expansion,
and high specific modulus. To expand the use of CFRP, we investigated the long-term stability of CFRP under humid
environment. CFRP mirror was made as precise as possible by using special class of material and adopting particular
design techniques. Dimensional stability of CFRP mirror was evaluated by nano-scale measurement. The factors which
cause out-of-plane deformation of the mirror is discussed.
FBG (Fiber Bragg Grating) sensors were embedded into CFRP unidirectional composite laminates in a direction
perpendicular to the carbon fiber. Residual strains after curing were evaluated by the reflection spectrum from the FBGs.
The CFRP laminates were kept at 100°C for monitoring of the residual strain change measured by the FBGs. Without
mechanical loading, occurrence of physical aging was confirmed by the residual strain changes. The relationship
between the influence of physical aging on residual strain and the thickness of the CFRP was almost linear.
This paper presents the health monitoring technique of composite repair patches using small-diameter fiber Bragg grating (FBG) sensors. The composite patch structures consist of carbon fiber reinforced plastic (CFRP) patches, aluminum substrates and adhesive layers. The debonding progressed between aluminum substrate and the adhesive layers under cyclic loading. In this research, two types of the specimen were prepared for evaluation of the debonding size. One is specimen with the patches glued on the both side of the aluminum plate. The other is pre-notched specimen for investigation of the influence of the crack propagation in the substrate. The FBG sensors were embedded into the adhesive layers easily, because the diameter of the sensor was only 52 μm. Reflection spectra from the sensor were measured at various lengths of the debonding. The form of the spectrum changed sensitively with an increase in the debonding size. For confirmation of the measured results, the spectra were simulated theoretically. As a result, the change in the calculated spectrum was consistent with that in the measured spectrum, and the relation between the spectrum and the debonding was clarified. Moreover, the debonding length was evaluated quantitatively by the monitoring of the form of the reflection spectrum.