Research On Damage Monitoring Methods Of Composite T-joints

Composite material has advantages of high specific strength and specific modulus, good fatigue and chemical corrosion resistibility and so on, so it is widely used in modern aircraft. A lot of composite structures are used in large areas of the civil airliners developed over the past decades. The internal damages of the composite structure are difficult to identify and detect from surface. Therefore, real-time damage monitoring can reduce the maintenance cost and condition-based maintenance instead of regular maintenance can improve efficiency of cluster management during the service progress of composite material.According to the complexity of propagation of Lamb wave in T-joint composite material, the paper analyses the propagation characteristics of Lamb wave in composite structure. Calculation of the group and phase velocities of Lamb wave is discussed. Characteristics of muti-mode and frequency dispersion are studied in theory and experiment. On this basis, the paper researches the propagation velocity of Lamb wave in composite plate structure.Based on the requirement of real-time damage monitoring of T-joint composite material,CCDI(correlation coefficient damage index),EDDI(envelope difference damage index), CLDI(curve length damage index)are proposed. Aiming at the admixture of wave packets in the ultrasonic damage detection of T-Joint composite material, a wavelet modeling method is proposed. The simulation results show that this method could not only distinguish a wave packet from others but also restrain noise.Experiments of real-time damage monitoring and early-warning of T-joint composite material are performed based on three damage indexes. Based on wavelet modeling method, ultrasonic imaging of damage in T-joint composite material is realized to verify the efficiency of monitoring method of damage index.