THE LIMITS OF POISSONS RATIO IN POLYCRYSTALLINE BODIES

While it has been established that the elastic moduli and compliances of anisotropic and isotropic materials should be positive for thermody namic reasons, no condition related to the values of Poisson's ratio h as yet been established. However, it is generally accepted that for is otropic materials Poisson's ratio should vary between - 1.0 and 0.5, w hereas for orthotropic materials various conditions have been introduc ed relating the different components of the anisotropic Poisson's rati o with the remaining elastic constants of the material. In this paper, limits for Poisson's ratio of body-centred cubic (bcc) polycrystallin e materials are determined, based on the modes of deformation of a typ ical unit cell of the material subjected to a uniform external loading arbitrarily oriented relative to the principal axes of the crystal. I t is shown that the values of Poisson's ratio thus established correla te satisfactorily with experimental values of this constant. The proce dure can be readily applied to other structural units of polycrystalli ne bodies.