Patent GB-954640-A (GB)
Title: Means for damping
IPC: E04B1/82
Filed: 1960-04-08
Abstract: 954,640. Laminates. BOLT, BERANEK & NEWMAN Inc. April 8, 1960 [May 5, 1959], No. 12656/60. Drawings to Specification. Heading B5N. [Also in Division F2] A structure for damping the flexural movements of a surface comprises a constraining layer that is substantially parallel to the surface, and at least one spacer layer and at least one damping layer disposed between the surface and the constraining layer, the layers and surface being attached to one another. The effect of this arrangement is that when the surface is flexed, its movements are applied in amplified form to the damping layer to shear it by relative displacement of its faces. The real term of the shear modulus of the damping layer is less than that of either the surface or the constraining layer; the real term of the shear stiffness of the damping layer is less than that of the spacer layer; the real term of the extensional stiffness of the spacer layer is less than that of the surface or of the constraining layer. The shear modulus is the ratio of shear stresss to shear strain measured dynamically under rapidly alternating shear stresses; the shear stiffness is the ratio of the real term of the shear modulus to the thickness ; the extensional stiffness is the product of the real term of the dynamic Young's modulus to the thickness. All three are complex quantities, i.e. each can be expressed as the sum of two terms of which one is real and the other imaginary. The Specification describes and illustrates (Figs. 1, 2, 4, 5 and 7-13, not shown) several embodiments : (Figs. 1-2) a single spacer layer, e.g. a light-weight metal, cardboard or other honeycomb, which may contain damping lossy material, rigid foamed polystyrene, rigid foamed polyurethane, balsa wood, expanded metals, ceramics, projections from the surface to be damped or corrugated structures, next to the surface, and a single damping layer next to the constraining layer, the damping layer may be a filled high polymer plastics compound, and the constraining layer of metal, these last two layers together comprise a conventional damping tape; (Figs. 4-5) as Figs. 1-2 except that the positions of the spacer and damping layers are interchanged; (Fig. 7) one damping layer sandwiched between two spacer layers; (Fig. 8) one spacer layer sandwiched between two damping layers; (Fig. 9) three damping layers alternating with two spacer layers; (Fig. 10) a waffle-like structure of rigid plastics material or metal serves as both spacer and constraining layers, damping material being placed between the depressions of the structure and the surface to be damped, a further constraining layer may be added if desired; (Fig. 11) a thick layer of expanded foam-like plastics, e.g. polystyrene, serves as both spacing and constraining layers, a damping layer is provided between it and the surface to be damped; (Fig. 12) two such thick layers are provided, and two damping layers, one between them, the other between one of them and the surface to be damped; and (Fig. 13) the spacer layer is sandwiched between two constraining layers, and the damping layer lies between one of these constraining layers and the surface to be damped. Specification 891,485 is referred to.