Research On Damage Testing Of Carbon Fiber Reinforced Plastic Adhesive-bonded ? Joints

Carbon Fiber Reinforced Plastic(CFRP)adhesive-bonded ? joint is a typical composite material orthogonal connection structure,used to transmit loads between different orthogonal planes.It is of great significance for the safety of aerospace to study the damage of CFRP adhesive-bonded ? joint and to monitor its internal damage by effective methods.Fiber Bragg Grating(FBG)sensor is very suitable for the damage testing of CFRP adhesive-bonded ? joint because of its small volume,light weight,and good compatibility with composite materials.However,the local stress concentration is serious and the gradient is large in the damage region of CFRP adhesive-bonded ? joint.Traditional wavelength demodulation can only be used to measure the average stress and strain in the sensing region,which will inevitably lose the gradient information of the stress field in the damage region,and lead to the inability to accurately monitor CFRP adhesive-bonded ? joint.In order to more accurately and effectively monitor the damage of CFRP adhesive-bonded ? joint,it is necessary to study the damage identification of CFRP adhesive-bonded ? joint and the measurement of non-uniform stress and strain in the damage region.To this end,the damage testing of CFRP adhesive-bonded ? joint based on FBG sensing was studied in this paper,which aimed to establish the relationship between the damage evolution and the distribution of stress and strain,and put forward a method for measuring non-uniform stress and strain in the damage region.These studies laid the theoretical foundation for the damage testing of CFRP adhesive-bonded ? joint.The main research contents of this paper are as follows:Based on the material mechanics and composite laminate theory,the stress state and damage criteria of CFRP adhesive-bonded ? joint under tensile loading were analyzed.The damage of CFRP adhesive-bonded ? joint under tensile load was calculated by finite element analysis software,and the relationship between the damage evolution of CFRP adhesive-bonded ? joint and the distribution of stress and strain in the damage region was analyzed and summarized.Through the tensile test of CFRP adhesive-bonded ? joint,it was verified that the embedded FBG sensor had no effect on the mechanical properties of the joints,and it was proved that the damage of CFRP adhesive-bonded ? joint could not be accurately judged and predicted by the shift of the center wavelength of the reflection spectrum.Based on the transmission theory of FBG,the reflection spectrum of the FBG sensing area of the CFRP adhesive-bonded ? joint was calculated by the transfer matrix method,and the peeling stress in the FBG sensing area of the CFRP adhesive-bonded ? joint was reconstructed with the particle swarm algorithm.The results demonstrated that the maximum error between the peeling stress and ideal peeling stress did not exceed 5.46%,and the gradient information of the peeling stress was well preserved.The measurement of the non-uniform distribution stress and strain was achieved,and the damage testing method of CFRP adhesive-bonded ? joint based on the reconstruction of peeling stress was obtained.