Structure Changes of Polymeric Materials under Large Deformation

为了研究玻璃化转变区变形引起的粘结结构变化，利用新研制的基于激光散斑法的应变仪，测量了聚苯乙烯在恒速拉伸变形过程中泊松比随时间的变化。在低应变率下测得的粘性增长函数呈现线性响应的比值随时间的变化，可以用粘弹性函数具有相同平移因子的约化变量的方法叠加到复合曲线上。得到的复合曲线由玻璃区的0.33变为橡胶区的0.5。然而，实验曲线与简单的线性响应理论预测的结果并不一致。这一结果可能归因于体积弛豫现象的强烈非线性。在较高应变率下，粘性增长函数表现为非线性响应，短时区泊松比增大。

Time evolution of Poisson ratio of polystyrene during elongation deformation with constant rates was measured by a newly developed tensile tester equipped with a strain gage based on LASER speckle method in order to study cohesive structure changes induced by deformation around the glass transition zone. Time evolution of the ratio measured at low strain rates, at which viscosity growth function showed linear response, could be superimposed to a composite curve by the method of reduced variables with the same shift factor for the viscoelastic function. The obtained composite curve changed from 0.33 in the glassy zone to 0.5 in the rubbery zone. However, the experimental curve was not in accord with the prediction by a simple linear response theory. This result may be attributed to strong nonlinear nature of volume relaxation phenomena. At higher strain rates, where viscosity growth function showed nonlinear response, Poisson ratio in the short time region increased.