Manufacturing of Composite Grid/Core/Skin Structures

Stephen Tsai and researchers at Stanford University's Structures and Composite Laboratory have designed a composite grid-stiffened skin structure, which is ultra-lightweight, stiff, strong, and easier and less expensive to manufacture. This construction can be made in one piece, with no fasteners, fully interlocked and outside of autoclave, and can replace the conventional three-piece spar/rib/skin structure. One unique feature of the grid is the use of finite length ribs placed in a staggered pattern, so all ribs have same dimensions and height to provide high stiffness and structural integrity.

Figure 1 Grid/Skin Structure
Image courtesy Stephen Tsai

Instead of using continuous tape mixed with discontinuous inserts, Tsai's new manufacturing method uses discontinous tape with length twice that between joints. The design lowers cost, has less waste, is ultra-light, tough, and strong. Its open structure ensures that inspection and repair will be easy. The grid/skin structure is suitable for a wide range of lightweight, strong structures including aircraft, space launch vehicle bodies, rockets, automotive panels, and battery cases.

Figure 2 Tsai's designed panel (MTorres manufactured) at Paris Air Show 2019.
Photo courtesy Stephen Tsai

Stage of Development – Proof of Concept Prototype
Tsai's design is ready for application and can be modified for a variety of load cases. Design and experimental iterations are ongoing and include comparison between the new finite length ribs versus continuous tape with discontinuos inserts in flat as well as curved and full barrel panels. For the 2019 Paris Air Show, MTorres manufactured Tsai's designed panel via resin infusion of dry carbon fibers (figure 2). It can also be fabricated using traditional thermoset prepreg. The proposed grid/skin construction is better than traditional isogrid for having only two rib directions instead of three, joint and ribs with the same height, and automated layup.