Study on the interlayer bonding property of dry fiber tows used in automated fiber placement for aerospace composites

In order to guarantee the good adhesion between layers of dry fiber preform, the interlayer bonding properties of two kinds of automatic fiber placement dry fiber tows were investigated, one has been maturely used in aerospace primary force-taking structure and the other one is under development. Dry fiber laminate samples were prepared by hot pressing to simulate the automatic fiber placement. The interlayer bonding property, surface properties and binder extension of dry fibers were measured by the T-type peeling test and various characterization methods. The interlayer bonding strength of the two kinds of dry fibers was compared and the interlayer bonding mechanism was studied. The results show that the interlayer bonding strength of mature dry fibers is much greater than that of developing dry fibers in a certain temperature range. Both of them are significantly affected by lamination temperature, lamination time and the synergistic effect, but the most significant factors of the two materials are different. The interlayer bonding mechanism of dry fibers is related to surface properties of dry fibers, properties of binder and the binder extension at elevated temperature. It is speculated that the interlayer bonding force of mature dry fibers is related to the crosslinking of the binder. In addition, through the verification of the automatic laying process, the hot pressing process has good reliability in the evaluation of interlayer bonding between the dry fiber layers within a certain lamination time comparing to the automatic fiber placement. Finally, when the dry fiber surface is coated with the thermoplastic toughening material, the adhesion between layers decreases significantly. Through the study of materials and technology, this paper provides data and theoretical support for the optimization of automatic fiber placement process.