Researchers at the Technology Innovation Institute (TII) in Abu Dhabi, UAE have been researching ways to join composite sheets using thicker carbon thread than previously used.

According to the researchers, if an airplane suffers damage, technicians need to securely patch a fresh sheet of material around the damage. However, joints where multiple sheets connect are not as strong as the rest of the composite sheet.

“Usually, the repair patch leads to weakened overall structure,” said Professor Zhongwei Guan, executive director at the institute. “With this approach, we are trying to affix a repair patch with the same strength as the mother material.” This could lead to sturdier products like airplanes and cars besides improving the strength of repairs, he said.

Currently, sheets are often stitched using thin wires with a diameter usually less than 1 mm. The researchers are exploring the characteristics of joining composites with carbon fiber threads of 2-4 mm in diameter. “It is important to balance out the strength of a thicker fiber thread against the effects of a larger diameter hole which weakens the fabric to be connected or repaired,” said Professor Guan. “This research is still in its early days because it is difficult to stitch using such thick fiber thread through a composite component with a large thickness. There are no machines to stitch these thick fiber threads with composite laminates or sandwich to date.”

The team is next focused on analyzing the relative performance of various kinds of single-lap and double-lap weaves. Once they have identified some of the best patterns and stitching techniques, they hope to develop a machine that can automate this process.

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