Simple Tensile Deformation of Silica-Filled Silicone Rubber and X-Ray Observation of Deformed Structure

Abstract

Silicone rubber with the silica content ranging from 15 to 48wt% was stretched under simple tensile loading. The experimental formula relating true stress to extension ratio was obtained and the constants in the stress-strain equation were correlated to the spring hardness of material. The internal structure of stretched silicone rubber was examined with the wide-angle X-ray method and the result was discussed in relation to its stress-strain behavior. The results obtained are summarized as follows:
(1) For the range of extension ratio λ up to about two, the true stress was expressed as a function of λ as
σ=3G(λ-1) or σ=2G[λ+1/(2√λ)]lnλ
and the shear modulus G was related to spring hardness H_S:
G=0.121exp(0.51 H_S).
When λ is between 1.4 to 3.6, the true stress is given by
σ=bλ^a,
where a and b are constants related to H_S as
a=0.361lnH_S+1.29 and b=0.31exp(0.048H_S).
(2) The increase in preferred orientation of the principal halo with extension ratio λ was found to be a sole function of λ, independent of the silica content. As stretching proceeded, the Bragg angle of the principal halo became larger in the direction perpendicular to the extension axis, while it showed no detectable change in the parallel direction. The half-value width of the halo decreased at a large value of λ. The degree of orientation in restretched rubber was smaller than that in the initial stretching when compared at the same λ-value.