Abstract: Traditional manual laying has the problems of unstable forming quality and low production efficiency, which is difficult to meet the production demand of the main bearing structure of complex composite materials. And the paving of the bearing structure with complex characteristics is impossible by automatic tape laying. Based on this, this paper proposes a preforming co-curing process on the basis of manual paving. Meanwhile, the effects of hand-made co-curing and preforming co-curing on the forming quality of composite hat-shaped structure are compared by using FBG sensor to monitor strain, combined with phased array ultrasonic detection, optical microscopic observation and mechanical properties test. The results show that the internal strain of the hat-shaped structure prepared by preforming is larger, which is mainly affected by the pressure in the autoclave and the silicone rubber auxiliary mold, and it is beneficial for the smooth distribution of fibers in the structure and better compaction effect. There are many kinds of internal defects in hat-shaped structure, which mainly exist in the triangle area and the joint of hat-shaped truss and skin panel. Compared with the hand-made co-curing process, the key areas of the hat-shaped structure in the preforming process (1 ℃/min heating to 60 ℃, holding for 1 h) are basically free of defects such as pores and fiber wrinkling, and the shape accuracy is evenly distributed, in which the pull-out strength is effectively increased by 21.5%.

Key words: composite, co-curing, hat-shaped structure, on-line monitoring, forming quality