Strain Energy Function of Poly(Propylene Oxide) and Polybutadiene Elastomers Estimated by General Biaxial Strain Testing

Abstract

Stress-strain relations of poly(propylene oxide) (PPO) and polybutadiene (PB) elastomers are investigated by general biaxial strain testing where the strains in two orthogonal directions are varied independently. The data for general biaxial deformation provide an unambiguous basis to estimate the form of strain energy function (W) governing the stress-strain relations of elastomers. The function W (I₁, I₂) = C₁₀(I₁-3) + C₀₁(I₂-3) + C₁₁(I₁-3)(I₂-3) + C₂₀(I₁-3)² + C₀₂(I₂-3)², where I₁ and I₂ are the first and second invariants of Green's deformation tensor and C_ij (i, j = 0, 1, 2) are the numerical coefficients, satisfactorily describes the data in the whole range of biaxial strain for the two elastomers.