有限変形下における加硫NBRの力学的性質に関する研究

抄録

For the purpose of investigating the mechanical properties of vulcanized rubbers under finite deformation, three kinds of NBR (Butadien-Acrylonitrile copolymer) vulcanizates of different degree of crosslinking were prepared, and their stress relaxation behavior under orthogonal biaxial deformation was observed. The results were compared with those of NR (Natural rubbuer). The results are as follows.
(1) It has been ascertained that engineering stress f₁ and f₂ under single step biaxial deformation (λ₁, λ₂) at t=0 can be expressed in such a simple form as, and consequently It has been found that the above relations are not valid in strict sense and that f_i should be written as and that φ_i depends on λ_i more than λ_j(i, j=1, 2., i≠j).
(2) The contour maps of ∂W(I₁, I₂, t=1.0min.)/∂I_i have been drawn by the method mentioned previously¹⁾. The nature of the slope of the surfaces are similar to those of NR at relatively small deformation region in (I₁, I₂) plane.
But, with increase of I₁+I₂, the contour lines of ∂W/∂I₁ and ∂W/∂I₂ are respectively oriented in the directions of I₁ axis and I₂ axis more sharply than those of NR. On the other hand, the dependency of ∂W/∂I_i surfaces on the degree of crosslinking has a typical property in that the surfaces come down with vertical shifting by decrease in the degree of crosslinking. This dependency is different from that of NR as mentioned previously.
(3) A postulation for W[W=w(λ₁)+w(λ₂)+w(λ₃)] proposed by Valanis and Landel²⁾ are found to be satisfactory in predicting the true stress σ¹¹-σ²³ and σ²²-σ³³ by using ∂W/∂λ which can be determined by strip-biaxial data with the use of the above postulation.
However the values of ∂W/∂I_i have not been predicted with reasonable accuracy from the ∂W/∂λ. This results are discussed in detail in this paper.