Researches On The Ultrasonic Evaluation Of Mechanical Properties Of Composites

Composites are widely used in advanced engineering fields such as aerospace due to the advantages of high strength and stiffness.However,in the process of manufacturing and serving,various mechanical problems of composite inevitably arise,which influence the mechanical properties of composite and cause safety hazard that cannot be ignored.Therefore,it is very important to detect the structural damages timely and further evaluate the mechanical properties of composite rapidly and accurately.Based on the ultrasonic non-destructive testing technology,we conduct a series of researches on the rapid detection and localization of composite structural damages and the rapid evaluation of mechanical properties of composite.The main contents and innovations include:1.Theoretical researches on ultrasonic guided wave propagation in composite laminates:Based on the structures of composite laminates,the propagation characteristics of ultrasonic guided waves in anisotropic composite laminates and the detecting principles of guided waves are investigated.Mainly based on the semi-analytical finite element method,a guided wave propagation model based on the mechanical properties of composite structure is derived,where the multi-modal dispersion curves are drawn,and the time-transient excited response waveform of guided waves in composite laminates are further calculated.2.Researches on rapid detection and localization of structural damages in composites:To meet the requirements of efficient detection of composite structural damages,a graph-in-graph convolutional neural network(G-GCN)model based on ultrasonic guided waves is proposed for damage detection and localization.G-GCN achieves better damage localization accuracy with fewer sensors by constructing spatial–temporal feature graph representations of the guided wave relationship information.Then,an ultrasonic guided wave testing experimental platform for composites is built to verify the superiority and reliability of G-GCN model.3.Researches on online evaluation of mechanical properties of composite laminates:Based on the theory of guided wave propagation in composite laminates,an online nondestructive evaluation method for elastic modulus of composites is established.An ultrasonic guided wave nondestructive testing platform is built,where only two guided wave signals are used to reconstruct the dispersion curves of the guided wave modes in the composite laminate.On this basis,an Elasticity Network(ENet)model for evaluating the elastic modulus of composite laminate is proposed,which uses the reconstructed guided wave dispersion curve to characterize the mechanical properties of composite laminates completely.Finally,simulations and experimental verifications are conducted to fully prove its effectiveness.4.Researches on guided wave-based detection technology in complex environment: The influence of operational and environmental conditions such as temperature on ultrasonic guided wave signals is studied.Considering two key environmental conditions: temperature and noise,a feature extraction method of guided wave signals based on singular value decomposition is proposed,where the temporal robust damage index(TRDI)is obtained to remove the adverse effects of environmental conditions.Guided wave signals with noise pollution and 20℃-60℃ temperature variations are used to verify the effectiveness of TRDI.