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Properties

with FM 94 adhesive, resulting in a 0.005 in. thick prepreg with a nominal fiber volume fraction of 59%. The prepreg is layed-up in different orientations between the aluminum alloy sheets. From 1990 to 1995, GLARE laminates were produced only as flat sheets. It was believed that the aircraft manufacturer would use these flat sheets to manufacture fuselage panels by applying the curvature, thickness steps, and joints, using conventional methods developed for metal structures (forming, bonding, riveting, etc.). Several studies showed the benefits in performance and weight of these GLARE shells, but they also indicated the high cost of these parts in comparison with conventional aluminum structures.

To reduce manufacturing costs, the self-forming technique (SFT), shown in Fig. 9.30, was developed. Autoclave pressure forms the laminate over external and internal doublers, because the stiffness of the package of thin aluminum layers and still uncured adhesive and fiber layers is low. Additional adhesive, of the same type as that used to impregnate the glass fibers in the prepreg, is also added at certain locations to adhere interrupted metal sheets to each other; adhere thin aluminum internal or external doublers to the aluminum layers of the laminate; and to fill gaps in the laminate which would otherwise remain unfilled. Two doubler splice concepts are shown in Fig. 9.31. The additional adhesive in the laminate has a much higher shear strength than the prepreg layers. This means that the splices manufactured using the SFT, where adhesive is added at those locations where load transfer from one metal layer to another occurs, are not critical regarding delamination during static or fatigue loading. In other words, the splice is not the weakest link in the panel strength.

Crane Suspension

Fig. 9.30. GLARE Self-Forming Technique*

Crane Suspension

Vacuum Handling System

Removable Rails

Fig. 9.30. GLARE Self-Forming Technique*

Overlap Splice Configuration

Adhesive

Metal Fiber Layer

Adhesive

Interlaminar Doubler

Interrupted Metal Layer

Adhesive

Interrupted Metal Layer

Fig. 9.31. GLARE Splice Concepts'

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