Analysis of sewed preforms by visual on-line monitoring of stitch-hole variations under compaction

Compression tests with a special compaction device were performed in order to evaluate mechanical and morphological properties of preforms. Reinforcing materials used for preforming were a noncrimp fabric and a woven fabric. The preforms were manufactured (reinforced) by means of a double lock stitch and various densely stitched patterns were developed. The deformation of stitch-holes under compression was monitored on-line by a video camera with a microscope lens. Compression stress–strain curves and the increase in fiber volume fraction of preforms under compaction pressure were determined in correlation to the sewing parameters. It was shown that the preform compression phenomenon changes with the density of the seam pattern. The results lead to a mathematical model which, fitting parameters have to be physically described in future.