A new fabrication technique for composite shells utilizing the statical-geometric properties of braided sleeves

Shells constructed from composite materials have several advantages over similar structures made from traditional materials. However, the high cost of manufacturing composite shells inhibits their use in commercial applications, where cost is a dominant concern. A significant factor of this cost is that current fabrication methods for continuous fiber composite shells require fibers to be placed on mandrels to obtain desired shapes. Commonly fibers are placed on a mandrel by three techniques: they are wound as filaments, put in laminate form and wrapped, or braided into tubes, called sleeves, and dressed to the mandrel. Often a new mandrel must be manufactured for each new part produced.

A new method of fabricating composite shells from braided sleeves has been developed in which different sleeves are nested to form a single assembly. This assembly is then subjected to loads so that different sleeves in the assembly manifest different levels of tension. Various shapes are realized by manipulating the patterns of forces on the sleeves, without necessarily incorporating a mandrel. Manipulating the sleeves in this manner is called statically controlling the geometry of the sleeves. By eliminating the mandrel from the fabrication process, statically controlling geometry offers to lower the cost of manufacturing high strength composite shells and render these structures cost effective for commercial applications.

This work demonstrates the feasibility of producing composite shells by the new fabrication method. Statically controlling geometry requires a statical-kinematic model for braided sleeves. The rotationally symmetric Chebyshev net was found to be an effective model for braided sleeves based on the results of an experimental study. After determining the model, a methodology was established to fabricate shells with the new technique. To carry out statically controlled geometry, simple equipment was constructed and shells of different shapes were fabricated from single sleeves and nested assemblies. Inflatable bladders were placed inside some assemblies to produce additional shapes. Statically controlled geometry was found a suitable method for fabricating many different shapes of composite shells.