Cord Stresses in Inflated Tires

Abstract

In order to calculate the stresses in the cords of an inflated tire, membrane theory is applied to the cord body. The equation describing the tire surface in terms of tire con struction parameters and cord properties has been given in the literature, but no solu tions have been reported, probably due to its complexity. A solution of this equation, obtained by numerical techniques on a digital electronic computer, is presented in this paper. It is shown how this equation is combined with the equilibrium equations of the surface and how the force components in the principal directions are determined and the cord stresses calculated. The cord stresses in inflated tires are nonuniform, decreas ing from crown to bead.The deformation of a simple cord network is considered, and it is shown how the cord stretch during tire expansion can be determined. It is found that the cord undergoes nonuniform stretch and shrinkage from crown to bead. These calcuations have been confirmed by experimental x-ray measurements on metal-shadowed cord. It is sug gested that the calculated and observed nonuniform cord stretch and shrinkage during tire expansion and curing are a direct result of the nonuniform cord tension.