Évaluation des performances mécaniques de stratifiés carbone-époxy préformés à l'aide de la couture "one-sided"

Abstract

Vacuum assisted resin infusion is a suitable molding process to manufacture large-scale or complex-shaped composite components, but there is a pressing need to automate the dry reinforcements layup process to meet aerospace quality and efficiency standards. Dry reinforcements preforming using automated one-sided stitching (OSS�) is one of the preforming process that can help meet this need. However, stitching may alter the laminate’s mechanical performance, and therefore must be used judiciously. This project aims to assess effects of OSS� on the mechanical performance of a variety of laminates in order to make recommendations on the ideal use of OSS� for the preforming of a stiffened panel (skin-stringer assembly). To do this, the characteristics and properties of stitched laminates are benchmarked against the ones of reference (non-stitched) laminates at each of the three stages of the research. During the first stage of the research, the effects of three process parameters (i.e. the stitching pitch, the molding strategy and the stitching orientation with respect to the loading direction) on the properties of a quasi isotropic laminate are studied using a series of physical and mechanical tests in order to select optimal process parameters for further work. Results for mechanical tests show that stitching the preform preserves, and slightly enhances in certain cases, openhole compression and compression after impact strength for specific combinations of process parameters. However, the use of OSS� causes a resin rich local laminate thickening (up to 0.5 mm) in the vicinity of the stitches that results in an increase of the laminate surface weight (between 3% to 9 %). To minimize the increase of the laminate surface weight while maintaining the mechanical performance, the stitching pitch must be maximized, the preform must be flipped between the stitching setup and the vacuum assisted resin infusion setup so that the top of the preform is placed against the rigid mold, and finally, the preform must be transversely stitched (with respect to the loading direction). During the second stage, effects of OSS� on the static mechanical properties of three (undamaged) laminates are studied. Results for tension, compression and flexure tests show that stitching reduces intralaminar strength, increases interlaminar strength and increases global stiffness for the three laminates. During the third stage, effects of OSS� on the damage tolerance of three laminates are studied. Results for open-hole compression, impact, compression after impact and Mode I crack growth tests show that stitching lightly increases compression strength of a damaged laminate, increases the total energy absorbed by the laminate during an impact and drastically increases interlaminar crack growth strength. Based on the effects of OSS� observed, recommendations on the ideal use of OSS� for the preforming of a "T-stiffened" panel are made. It is recommended to (1) minimize stitching density if a panel is heavily loaded in the in-plane direction, (2) maximize stitching density if a panel is likely to be damaged by an impact, and (3) stitch the web and the flange of the stringer as closely as possible to the central noodle to reduce risks of interlaminar crack propagation.

Date	15 Jan 2015
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Simon Joncas (Supervisor)