非ニュートン流停止後の応力緩和(Na-Polyacrylateの最長緩和機構)

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It is assumed that the substances described in the present paper have elements of viscoelastic mechanism which are non-linear at large stresses, but become linear at small stresses in behaviors of flow and internal deformation. In this case the generalized Maxwell formula (1) may be reduced to Eq. (2) at the terminal region of stress relaxation following non-Newtonian flow. [numerical formula](1) (2) The asterisk in the equation refers to small stresses. τ^°_j is the relaxation time of the jth mechanism in its ordinary sense at small stresses. By integrating Eq. (2) [numerical formula] (3) whereσ_j (0), as an integration constant, is the extrapolated value of the stress to t=0, under which the viscoelastic mechanisms obey Newtonian and Hookean laws. Dividing Eq. (3) by Υ^°: where η_j (0)=σ_j (0) /Υ^゜・On the analogy of the linear viscoelastic theory η_j (0) seems to be equal to η^°_j =τ^°_j G^°_j which may prevail in the viscoelastic behaviors under small stresses. If t>>τ^゜_m (the slowest relaxation time), Eq. (4) will become: where mechanisms of smaller relaxation time than τ^°_m are neglected. According to the theory presented here, the relaxation curves plotted by log{σ(t)/Υ^゜} vs. t must become a single straight line at the final process of relaxations, independent of Υ°values under the steady flow. However, the experimental curves for the materials investigated here become almost straight lines in parallel after the initial rapid relaxations. This phenomenon may be interpreted by the following formula.
1966-05-15

非ニュートン流停止後の応力緩和(Na-Polyacrylateの最長緩和機構)

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