Internal Damage Analysis of Braided Composites Embedded in Carbon Nanotube Yarn

Carbon nanotube (CNT) yarn sensors were embedded in 3D braided composites in the form of arrays to detect the internal damage of specimens and study the internal damage monitoring of the 3D braided composites. The signals collected by the sensor array of CNT yarn were preprocessed using the dynamic wavelet threshold algorithm. The exact position of the damage was calculated based on the main features of the resistance signal matrix, which was calculated using the quadratic matrix singular value. The results show that the internal damage localization of the specimens was consistent with the actual damage. The localizations in this study can provide a basis for enhancing the structural health monitoring of smart 3D braided composites.

Strain-Sensing Characteristics of Carbon Nanotube Yarns Embedded in Three-Dimensional Braided Composites under Cyclic Loading

Carbon nanotube yarns are embedded in three-dimensional (3D) braided composites with five-axis yarns, which are used as strain sensors to monitor the damage of 3D braided composites. In the cyclic mechanical loading experiment, the strain-sensing characteristics of 3D braided composites were studied by in situ measuring the resistance change of the embedded carbon nanotube yarn. The 3D five-directional braided composite prefabricated part based on carbon nanotube yarns was developed, and the progressive damage accumulation experiments were carried out on carbon nanotube yarns and specimens embedded in carbon nanotube yarns. The research results show that there is a good correlation between the change of relative resistance of the carbon nanotube yarn and the strain of the composite specimen during cyclic loading and unloading. When the tensile degree of the specimen increases beyond a certain range, the carbon nanotube yarn sensor embedded in the specimen shows resistance hysteresis and produces residual resistance. Therefore, the fiber can better monitor the progressive damage accumulation of 3D five-direction braided composites.

A parameterized unit cell model for 3D braided composites considering transverse braiding angle variation

In this paper, a parameterized unit cell model for 3D braided composites considering transverse braiding angle variation is proposed, to assist the mechanical characterization of such materials. According to the geometric characteristics of 3D braided composites, a method for automatically generating textile geometries based on practical braiding parameters, including the main braiding angle, the transverse braiding angle, and the fiber volume fraction, is established and implemented in a CAD software package. In this model, the addition of transverse braiding angle educes a more flexible control of fiber volume fraction distribution, and with the combination of control parameters according to the actual fiber distribution needs of users, it can suggest the appropriate parameters for the unit cell. The generated unit cell models are used in finite element analysis and the results are validated against experiments for a number of 3D braided composites in terms of fiber volume fraction and elastic constants, and good agreement is observed. Based on the parameterized unit cell model, the effects of main braiding parameters on the elastic properties of 3D braided composites are discussed.