非晶聚合物玻璃化转变附近的弱非线性蠕变：模型与实验的比较
Weakly non-linear creep of amorphous polymers near their glass transition, comparisons between models and experiment
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中文总结 AI 辅助
本研究对比2S、SC、FEM三种模型与实验，探究非晶聚合物玻璃化转变附近非线性蠕变的局部与全局加速关系，发现SC、FEM可复现实验的蠕变加速趋势，证实非线性相互作用产生的异质性对宏观力学响应的重要性。
中文摘要 AI 辅助
非晶聚合物在玻璃化转变附近的非线性力学行为表明，应力会诱导纳米级亚单元的应力松弛加速。近期理论研究预测，这些纳米域内的局部加速应与局部应力平方的指数成比例，该行为现已得到实验支持。然而，这种局部动力学对宏观力学响应存在复杂影响，因为在接近玻璃化转变的聚合物中，动力学异质性会产生复杂的应力和应变场。本研究针对非晶聚合物在玻璃化转变附近的非线性蠕变，通过将实验数据与三种复杂度递增的模型（两态（2S）模型、自洽（SC）模型、有限元（FEM）模型）的预测结果进行比较，评估局部加速与全局加速的关系及新兴承载结构。实验观测到的“施加应力增大时蠕变加速”的趋势，SC模型和FEM模型均可复现，而2S模型高估了应力局域化。宏观均匀化加速被预测接近微观加速，但存在一个与柔度相关的表观屈服应力。FEM模型证实，由亚域相互作用驱动的承载亚结构会占据材料总体积的一小部分。本研究表明，非线性相互作用会产生复杂性与异质性，而对其进行恰当表征对于预测非晶聚合物在玻璃化转变附近的宏观力学响应至关重要。
英文摘要
The non-linear mechanics of amorphous polymers near the glass transition reveals a stress-induced acceleration of stress relaxation of nanometric sub-units. Recent theoretical work predicts that the local acceleration within these nano-domains should scale as the exponential of the squared local stress, a behavior now supported by experiments. However, this local dynamics has some complex consequences on the macroscopic mechanical response, as dynamical heterogeneities generate complex stress and strain fields in polymers close to the glass transition. In this study we consider the non-linear creep of an amorphous polymer near its glass transition and evaluate the relation between local and global acceleration and the emerging load-carrying structure, by comparing experimental data with predictions of three models of increasing complexity: a two-states (2S) model, a self-consistent (SC) model and a finite-element (FEM) model. The experimentally observed trend of accelerated creep under increasing applied stress is reproduced by the SC and FEM models, while the 2S model overestimates stress localization. The macroscopic, homogenized acceleration is predicted to be close to the microscopic one, albeit with an apparent yield stress that depends on compliance. The FEM model evidences the development of a load carrying sub-structure that occupies a small fraction of the total material volume driven by the interaction of sub-domains. This work shows that complexity and heterogeneity emerge due to non-linear interactions and that their adequate representation is essential for predicting the macroscopic mechanical response of amorphous polymers near their glass transition.
