Poisson's Ratio for Honeycomb Sandwich Cores

Abstract

0.1 0.2 0.3 0.4 0.6 PsMs 0.8 1.0 2.0 constant specific heats, constant Prandtl Number, isothermal wall, and similar boundary-layer profiles. The latter assump­ tion—'that is, that the dimensionless velocity and thermal pro­ files are functions of a single variable—is physically correct at the stagnation line of the cylinder. Values of the heat-transfer parameter obtained from these solutions are plotted in Fig. 1 versus the ratio (psp:s/pw^w) where subscript s now denotes values in the external flow at the stagna­ tion line of the cylinder as well as the stagnation point of a body of revolution. The solutions for /3 = 0.5 and X = 1.0 are applied to a body of revolution by the use of Mangler's transformation relating two- dimensional and axisymmetric flows. Since the Sutherland viscosity formula and constant Prandtl Number are used in reference 1, as well as in the present solutions, the close agreement between the present results for (3 = 0.5 and Eq. (1) indicates that the heat-transfer parameter at a stagnation point is not sensitive to the effects of dissociation on density and specific heat within the boundary layer. For equilibrium disso­ ciation and Lewis Number 1, the heat-transfer rate at a three- dimensional stagnation point can then be calculated from the equation1 qw = VPwfjLw(dUe/dx)s ((hs - hw)/a) (Nu/VRe). (2) where the symbols are those of reference 1, and all quantities are evaluated in the real-gas flow except {Nu/\/Re) which may be obtained from either Eq. (1) or a solution of the boundary-layer equations for a perfect gas with Sutherland's viscosity formula provided that the value of psVs/pwVw applying to the solution is equal to the real-gas value. The heat transfer at the stagnation line of a yawed cylinder is also calculated from Eq. (2) except that hs should be replaced by the adiabatic wall enthalpy given by the equation2 A N INTERESTING mechanical property of honeycomb cores is •^ *• their Poisson's ratio: it is very sensitive to cell geometry and can assume values from zero to about three. Large values may be observed when flexing some slabs of honeycomb with flat cell walls, while rippled-wall honeycombs demonstrate zero Poisson's ratio. The ratio of anticlastic curvatures is indicative of the value of Poisson's ratio for axial loading in the plane of the slab.