Abstract:

In order to realize in-situ structural health monitoring of 3-D braided composites, 3-D five-directional braided composite preforms embedded with carbon nanoyarns were prepared, a carbon nanoyarn strain sensing experimental system based on 3-D braided composite specimens were established, and the strain sensing  characteristics of carbon nanoyarns embedded in 3-D braided composites were analyzed. The results show that during the  process of monotonic stretching and cyclic loading and unloading, the resistance change rate of carbon nanoyarn sensors embedded in 3-D braided composites and the strain of specimens maintain a good linear correlation. After cyclic loading and unloading under heavy load, the residual resistance generated by the carbon nanoyarn sensors can be used to detect the damage or cumulative damage of specimens. The strain sensing equation for the net difference of resistance change and the net difference of mechanical strain established after introducing the coefficient of correlation of resistance to strain could achieve in-situ structural health monitoring of 3-D braided composites.

Key words: 3-D braided composites, structural health monitoring, carbon nanoyarns, strain sensing characteristic, correlation of resistance to strain