Abstract: In order to study the tensile deformation, damage and failure behavior of carbon fiber three-dimensional braided composites, the acoustic emission and digital image correlation complementary techniques are applied to the study of carbon fiber three-dimensional and four-directional braided composites. Meanwhile, acoustic attenuation characteristics, tensile deformation and damage destruction processes are monitored simultaneously. Besides, the corresponding speckle images and AE characteristic signals are acquired dynamically. Then the related calculations and AE signal processing are performed. The results show that the attenuation of the composite along the braiding yarn direction is significantly lower than that of other directions, and the farther the distance between the broken lead and the sensor is, the greater the attenuation amplitude is. At the early stage of the specimens loading, AE signal levers are a bit low and the displacement fields as well as strain fields change steadily. In the accumulation phase of damage, the relative energy of AE increases gradually, and the material exhibits obvious elastic deformation characteristics. When the load reaches the maximum value, both the displacement and strain values in the tensile direction and the horizontal direction reach the maximum, and the specimen fails and fractures. The comprehensive monitoring and analysis of AE and DIC can better describe the damage evolution and destruction process of the specimen, and provide reference for the safety evaluation and health monitoring of carbon fiber three-dimensional braided composites.

Key words: 3D braided composite, sound velocity attenuation, acoustic emission, digital image correlation