Research On Monitoring Of Cure Process And Low-velocity Impact Damage Of Composite

The composite materials have been widely used in aerospace, naval, and civic structuresfor its excellent mechanical and physical properties. Long-term monitoring and control ofstructure’s response to dynamic and impact loads are needed to keep the structure safe. Since theemergency of optical fiber technologies, various types of sensors, like intensity-based or opticalcavity based sensors have been investigated for their use in composite structures. Fiber Bragggratings (FBG) have been proved to be promising for temperature and strain-sensing applications.Since then FBGS are extensively used in structural monitoring of fiber reinforced compositestructures.FBG is in low density, small size, and high sensitivity and minimally invasive, so it isbecoming one of the main methods of internal structure monitoring. FBG integrated in thecomposite can monitor the real-time damage，fatigue and impact beard by the structure, we canknow whether the structure is safe by analyzing the change of the wavelength, the safety can beguaranteed by fixing or changing the broken component in time.Grating sensing mechanism for temperature and strain was analyzed in this paper,temperature and strain sensing coefficients were also measured through experiment. Laminatespecimens were made with the integration of FBG by VARI. The test result showed that FBG wasin high sensitivity to temperature and strain, its wavelength signal was steady under hightemperatures.The curing process was monitored by the FBG embedded in the laminates; the stackingsequence’s effect to residual stress was analyzed. The result showed that FBG can capture the fourstages of curing process; the gel time can be achieved by analyzing the wavelength curve; the shiftvalue of the wavelength reflect the residual stresses. This could give some references to developthe curing process. In order to study the effect of low velocity impact to laminate using FBG sensors, thefailure mechanism was studied in this paper. Then a series of impact tests were conducted to studyFBG sensor’s sensitivity to impact. The monitoring data showed that FBG could accurately catchthe strain change of the laminate under impact; the damage of laminate was inspected throughvisual inspection and C-scan, it showed that the change value of the wavelength can reflect thedamage situation of the laminate.The signal of FBG to quasi-static compression was also monitored. The result showedthat the trend of the change of wavelength under quasi-static compression was similar to thechange curve under low velocity, so it has certain feasibility to study the impact behavior by usingquasi-static compression test.