C

HOIcc-Zf

Fig. 11-39. Equations for the Mass and Moment of Inertia for Some Common Solids. For a solid of uniform density, p, the mass is the product of p and volume. We use the parallel axis theorem to find inertias at axes B-B. MOIgg = MOIjm+md2 where d is the distance from the A-A to B-B axes.

Sandwich structure consists of a lightweight, shear-resistant core bonded to outer face sheets (Fig. 11-40). A sandwich panel acts like an I-beam. The faces correspond to the top and bottom flanges of the beam and resist in-plane bending, tension, and compression. The core acts like the I-beam's web and carries shear and out-of-plane loads, while providing support for the faces.

Fig. 11-40. Sandwich Panel with Honeycomb Core. By separating thin face sheets with a lightweight core, we efficiently increase tine bending strength and stiffness of a panel or shell. Increasing the bending stiffness raises the buckling strength.

Face sheets and cores can be of nearly any metallic or composite material. The core is usually formed into corrugations or honeycomb cells built from thin strips called ribbons. Core properties are not isotropic, as stiffness in line with ribbons is greater than transverse stiffness. To maintain die structural integrity of a sandwich, we must make sure the adhesive bond between the core and face sheets is consistent See Brutin [1973] for detailed sandwich analysis. Figure 11-41 shows how sandwich structure can be stiffer than skin-only designs.

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