Abstract:

In order to study the real-time monitoring of the internal damage of large-size 3-D braided composites, the fiber Bragg gratings (FBG) sensors were embedded in the 3-D braided composite preform according to the braiding characteristics of 3-D six-directional braided composites. Amethod for producing large-size intelligent composite materials was proposed. The tensile characteristics of the FBG sensor inside the composites was studied. Based on the principal component analysis method, the damage detection algorithm of the specimen structure was proposed. The damage index performance characteristics of the four samples with the same damage were analyzed. The experimental results show that the FBG sensor can accurately measure the internal damage of the composite. The damage index can describe the damage degree of the specimen sturcture. The T² index and Phi index can diagnose the occurrence of internal damage of the specimens more quickly. For the same damage of the sample, the Phi index is calculated to be more than 2 times of the T² index, and the Phi index can be used to judge whether the interior of the sample is damaged in time. Q  index and I index describe the details of the damage more accurately.

Key words: three-dimensional six-direction braided composite, fiber Bragg grating, damage location, combined damage index, strain sensor