Study On The Low Velocity Impact Rule Of CFRP Laminates Based On FBG Sensor

Carbon fiber reinforced composite materials for aircraft structures in theoperation process will inevitably encounter some impact, causing the low speedimpact damages, most of which appear in the internal structure of compositematerials and are not easy to be visible to naked eyes, and greatly reduce the stiffnessand strength of the structural components. This thesis mainly uses fiber Bragg grating(FBG) sensor to monitor and analyze the low speed impact damage on the carbonfiber reinforced composite laminates, then we can obtain the low speed impact rules.This issue adopts the autoclave molding process to prepare the carbon fibercomposite laminate with embedded FBG sensors in the tests, impacting it at the lowspeed, and analyze the detected impact signal. The impact tests are carried out tochanging the impact energy, impact times, the way to embed the FBG and layer’s way.Through the experiments, the following conclusions are drawn:1. The wavelength drifted value increases nearly8times with the increase of impactenergy from2J to10J.The wavelength change of FBG sensors adds gradually withthe increase of impact times. And the damage of laminates impact back is also moreand more obvious.2. The different distances to the impact point (1#.2#.3#) and the different interlayers(4#.5#.6#) of FBG sensors which embedded in laminate can reflect the differencesof impact signal, more near to the impact point location, the wavelength change ismore obvious. After10times cumulative impact, the wavelength change value of1#grating is89.11pm, which is the4times as great as that of2#grating wavelengthchange value and7times of3#grating wavelength change value. The wavelengthchange value of4#grating is270.95pm, the wavelength change value of6#grating is475.13pm, Which is respectively10times and17times of5#grating wavelengthchange value. In the process of impact, the grating which is nearest to the impactpoint can reflect the internal impact damage of the laminates more distinctly, thewavelength change of grating embedded in laminates lower-middle-class is greaterthan the upper grating wavelength values. The tensile stress on the back of laminate isbigger than the compression stress value of impact surface. 3. By studying the different layer’s modes of the laminates and the impact wavesignal, comprehensive consideration, we decide to use [45/0/-45/90]2slaminates in thewhole impact experiment, so that we can judge and assess the impact damage of thelaminates better.The calculated relationship between the pit depth and the impact energy of[45/0/-45/90]2slaminates agrees well with the response of monitored signal by FBGsensors. Analysis of compression strength after impact tests (CAI) of [45/0/-45/90]4slaminates shows that the CAI value is reduced by55%with the increase of impactenergy. Also, by analysing tension-tension fatigue test of [0]12laminate withembedded FBG, the results reveal that FBG sensor signals can real-time respond tothe damage forms of materials in the fatigue process more quickly.