一般注記type:Thesis
The characterization and understanding of the crack-growth in elastomers have been an important issue both in polymer physics and industrial rubber products. In this thesis, two characteristic phenomena are investigated experimentally and analyzed while focusing on the effects of nonlinearity in elasticity and/or viscoelasticity: (1) the crack-growth rate v transition between two distinct regions of the slow mode and fast mode with the small change in the input tearing energy Γ, and (2) a power-law relationship between v and Γ in the fast mode region. The types of rubber and filler, concentrations of filler Φf and cross-link cx, and temperature T are extensively varied in order to change the degree of nonlinearity in elasticity of the elastomers. The shapes of crack-tip are characterized by two specific parameters, i.e., the deviation δ from the parabolic shape expected by linear elastic fracture mechanics (LEFM) and the parabolic curvature a. The Γ dependences of δ and a are successfully explained by weakly nonlinear elasticity theory of dynamic fracture (WNLT), which considers the second-order nonlinear effect in elasticity to LEFM, unless δ exceeds a limit value δc, independently of the types of rubber and filler, Φf, cx, and T. The value of δc depends on types of rubber and filler, whereas it is independent of Φf, cx, and T. The magnitude of the threshold tearing energy Γc for the onset of the crack-growth rate transition shows a good correlation with the fracture toughness Wc reduced by μ(1)3/μ(2)2 (μ(1): linear shear modulus, μ(2): second-order shear modulus), which is a measure of the nonlinearity in elasticity in WNLT. This result indicates that Γc is governed by the combined effect of the degree of nonlinearity in elasticity and the fracture toughness. A power-law relationship between v and Γ, i.e., Γ ~ vα, is also investigated. We find a universal relation between α and the exponent κ of the stress relaxation function G(t) ~ t-κ in the glass-rubber transition regime in linear viscoelasticity. The relation between α and κ is successfully explained by the existing theories which consider the contribution of linear viscoelasticity to LEFM for elastomers with low Φf and high cx, whereas that for elastomers with higher Φf and lower cx exhibits a finite deviation from the theoretical expectation.
連携機関・データベース国立情報学研究所 : 学術機関リポジトリデータベース（IRDB）（機関リポジトリ）