Standards Development

Scope

Two methods for the determination of the modulus or rubber in pure shear from measurements of the stress-strain behavior of a test piece under biaxial. In the first method the test piece, in the form of a sheet, is strained directly by the application of two orthogonal forces in the plane of the sheet. In the second, the test piece is clamped against a circular orifice in such a manner as to provide a fluid tight seal and restrain the sheet when a pressure is applied to one side. Provision is made to apply a pressure to one side of the sheet to produce which is effectively pure shear.

In both cases , the deformation of the rubber is measured as a function of the stress applied to the sheet.

Purpose

The prediction of the behavior of rubber components under load by finite element analysis is of growing importance. Finite element methods usually require a knowledge of the physical properties of the rubber, in particular the modulus in shear and, in some cases, the bulk modulus. The preferred method for the shear modulus is to determine the modulus in pure shear by measurement of the properties of sheet material under biaxial extension. The two deformations are equivalent for rubber-like materials (see Treloar1). For the purposes of this measurement, it is assumed that the material under test is isotropic, and the stress and strain in the two principal axes in the plane of the sheet are the same.