Damage Deformation Optical Non-destructive Measurement And Acoustic Emission Response Characteristics Of Composite Bonding Interface

In recent years, composite materials in advantages of its high specific strength, high stiffness, good fatigue resistance and so on, have been widely used in aerospace, energy, marine, automotive and other fields. Under the background of the rapid development of the aerospace industry, composite aircraft structures have put forward strict demand for non-destructive testing of aircraft. The composite lightweight design concept has been widely infiltrated into the process of design, processing and manufacturing of shipbuilding, automobiles, aircraft. Therefore, the study in terms of properties of the composite structure has great significance. The researches of the paper are as follows:Firstly, in order to research the bending damage characteristics and acoustic emission(AE) response behaviors of composite laminates with detects, four-point bending tests and real-time AE monitoring of composite materials embedded with delamination in different depth were conducted. The results show that the total number of cumulative hits and the maximum values of AE relative energy of the specimen with delamination embedded in the near surface are higher than those in the middle layer obviously. The bearing capacity of the specimen is apparently affected by the location of delamination defect. As the depth of the delamination defect from the specimen surface decreases, the loading capacity of the specimen reduces and aggravates the damage failure process of the specimen. AE features parameters such as amplitude, cumulative hits, relative energy and location are correlated with the damage process of composite materials embedded with delamination defect.Secondly, research on damage deformation and evolution behavior of adhesively bonded composite joints in real-time are of great importance for structural safety and its reliability assessment in service. In this paper, use of Digital Image Correlation(DIC) and AE as complementary techniques for studying interfacial damage, deformation and failure behavior of adhesive-bonded composite single-lap joints under cyclic tension. On the basis of the average tensile failure load value, cyclic tensile tests were conducted with 70% and 80% of quasi-static failure loading, respectively. According to the damage deformation field, strain field information, and AE signals originated form damage of adhesive-bonded composite single-lap joints at different stages, the relationships between the mechanical failure mechanism of composite single-lap joints and the corresponding real-time deformation and AE signals were analyzed. The results show that the real-time micro-displacement field, AE relative energy, cumulative hits and amplitude spectra obtained form damage and failure of adhesive-bonded composite single-lap joints are connected with the initiation and propagation behavior of microcracks at adhesive interfaces. As the stress levels increase, the number of loading cycles that the joints can sustain before failure decrease. DIC and AE test results play an important role for non-destructive evaluation and health monitoring in bonded composite structures.Thirdly, the tensile test on adhesively bonded T joints were combined with DIC and AE technology. The results show that: the displacement fields and the character of acoustic emission signal of bonding interface can characterize the process of bonding interface damage and failure, the position of embedded defect on bonding structure has a significant impact on its carrying capacity.