The Plane Elastic Characteristics of Cord—Rubber Laminates

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Abstract
Results from an experimental study on rayon and nylon tire cords embedded in rubber are reported. Stress-strain curves in tension and compression on thick-walled cylinders of such materials show that much higher moduli of elasticity are exhibited by cords under tension than by cords in compression. However, the compression modulus of twisted cords is not insignificant, and such cords can apparently carry appreciable compressive loads when properly encased in rubber and when prevented from buckling. A bilinear approximation to the stress-strain curves of such materials is proposed as a means for approximate structural analysis of members utilizing these materials. Based on such a bilinear approximation, an analysis is presented for the state of stress and deformation in a laminated cord-rubber sheet under plane loads, using the principles of orthotropic materials. It is shown that four elastic constants are sufficient to describe the properties of a typical two-ply laminate when all cords are loaded in tension; a different set of four apply to the same body when it is loaded in such a way that the cords in both plies are in compression. The existence of interply stresses between lamina in built-up cord-rubber sheets is shown, and expressions are derived for the magnitude of such stresses as functions of the externally applied forces. Two different types of interply stresses are identified. Experiments were performed using laminated cord-rubber cylinders under various stress states in order to compare various moduli of elasticity with those predicted from theory. Such comparisons seem to indicate that the theories proposed adequately describe the composite materials being considered. It may generally be concluded from the work reported here that the elastic properties of any type of cord-rubber laminate may be derived from the elastic properties of a single sheet of its constituent material.

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