Modeling the rate-dependent ductile-brittle transition in amorphous polymers

非晶态聚合物的速率相关韧脆转变模型

The stress response of amorphous polymers in the glass transition region shows apparent temperature and rate dependence.With increasing loading rate,amorphous polymers also exhibit a clear ductile-brittle transition of tensile failure.The rate-dependent behaviors originate from intrinsic relaxations,ranging from perturbation of molecular bonds between polymer segments to reptation of polymer chains.In this work,we develop a constitutive model that incorporates segmental and chain dynamics into the deformation of bond and polymer networks,respectively.The dynamic scission of polymer chains is also incorporated into the theoretical framework to describe the damage evolution and ultimate failure of polymers.A comparison between theoretical predictions and experiments shows that the present model is able to simultaneously capture the observed rate-dependent features,including the transition from glassy state to rubbery state,strain hardening,and failure threshold.

非晶态聚合物在玻璃化转变区的应力响应表现出明显的温度和速率依赖性.随着加载速率的增加,非晶态聚合物也表现出明显的拉伸破坏的韧脆转变.速率依赖性行为起源于固有的弛豫,从聚合物链段之间分子键的扰动到聚合物链的滑移.本文建立了一个本构模型,将键段动力学和链动力学分别纳入到键和聚合物网络的变形中.聚合物链的动态断裂也被纳入到描述聚合物损伤演化和最终失效的理论框架中.理论预测和实验结果的比较表明,该模型能够同时捕获观察到的速率相关特征,包括从玻璃态到橡胶态的转变、应变硬化和失效阈值.