繊維学会誌
Online ISSN : 1884-2259
Print ISSN : 0037-9875
ポリエチレンフィルムの伸長挙動に対する温度と伸長速度の影響
山口 拓治扇野 博明柳川 昭明木村 里雄
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1976 年 32 巻 11 号 p. T458-T470

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Stress-strain curves for polyethylene films have been measured at various temperatures from 20 to 100 C under different rates of extension over a range of 3.5 decades. Applicability of different superposition principles (model I, II and III) defined in the previous paper to non-linear stress-strain curves has been investigated.
Generally, non-linearity in stress-strain curve decreases with increasing temperature and increased with increasing strain rate. The non-linearity of low density polyethylene is weaker than that of high density polyethylene.
Seemingly, effects of time t and strain ε on stress σ are factorizable so that the secant modulus K (t, ε)=σ (t)/ε equals f (ε) H (t). Therefore the master curve of log K reduced to any strain ε0 can be composed by only vertical shift in log K-log t plots, However, the relaxation modulus at 1% strain calculated from the equation Er (t, ε)=K (t, ε) [1+(dlog K (t, ε)/dlog t)] does not agree with the observed values in the previous paper. Therefore, the superposition principle of model I is not applicable to the case of a constant rate of elongation for polyethylene.
In the theory of model III, if the reduced factor aε (ε) for master relaxation curve satisfies certain conditions, the master curve of secant modulus can be composed and log aε (ε) is obtained from the following equation: where log bε, is the horizontal shift factor for the master curve of log K. But the calculated values from above equation do not agree with observed values in the previous paper. Then stress-strain curves are directly calculated from the superposition principle. Generally, the predicted values from model III agree with observed curves compared to other models. However, appreciable differences between theory and experiment exist at 60_??_80°C as the strain rate increases. The cause of this disagreement is to be sought in neglecting the effect of strain rate on non-linearity in calculation.
Master curves of the secant modulus at each same strain reduced to 20°C are composed by only horizontal shift. Temperature dependences of shift factor log aT are qualitatively similar to those of log aT used to compose master relaxation curves in the previous paper. However, apparent activation energies are unreasonably large as compared with the prevailing data.

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