Abstract This paper deals with molecular ordering in polymers that exhibit strain-induced phase transformation accompanied with plastic yielding. The study is motivated by the anisotropic effects caused by the molecular ordering during the progressive strain-hardening, and thus attempts to contribute to the understanding of the strengthen mechanisms in initially isotropic glassy polymers. The application is performed on an initially isotropic amorphous polylactide that exhibits strain-induced mesomorphization and crystallization, whose respective development strongly depends on temperature and strain-rate. A micro-macro constitutive model is presented for the description of the polylactide macro-response along with the strain-induced chain orientation and anisotropy, the thermal-induced chain relaxation and the strain-induced phase transformation. A three-phase representation of the material microstructure allows accounting for the effective contribution of mesophase and crystalline phase both to the elastic-viscoplastic intermolecular resistance to small-moderate deformations and to the hyperelastic molecular network resistance to large deformations. The latter makes use of microsphere approach to render it anisotropic, the newly formed phases being distributed on each stretched molecular chain of the network thanks to the transition from the macro-scale to the micro-mechanisms at the chain-scale. The model results are compared favorably to experimental data up to very large strains and over a wide range of temperatures across the glass transition. The role of the molecular network orientation and the newly formed phases on the strengthen process of polylactide is highlighted. The model capabilities to predict continuous relaxation combined with heating at various temperatures are presented.

中文翻译：

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生物聚合物中应变诱导分子排序的微观宏观本构模型：在广泛的温度范围内应用于聚乳酸

摘要 本文讨论了聚合物中的分子排序，这些聚合物表现出应变诱导相变并伴随塑性屈服。该研究的动机是在渐进应变硬化过程中分子排序引起的各向异性效应，因此试图有助于理解最初各向同性玻璃态聚合物的强化机制。该应用是在最初各向同性的无定形聚交酯上进行的，该聚交酯表现出应变诱导的介晶化和结晶，其各自的发展在很大程度上取决于温度和应变速率。提出了一个微观宏观本构模型，用于描述聚乳酸宏观响应以及应变诱导的链取向和各向异性、热诱导的链松弛和应变诱导的相变。材料微观结构的三相表示允许解释中间相和结晶相对弹性-粘塑性分子间对小中度变形的抵抗力和对超弹性分子网络对大变形的抵抗力的有效贡献。后者利用微球方法使其具有各向异性，由于从宏观尺度到链尺度的微观机制的转变，新形成的相分布在网络的每个拉伸分子链上。将模型结果与高达非常大应变和玻璃化转变温度范围内的实验数据进行比较是有利的。强调了分子网络取向和新形成的相在聚乳酸强化过程中​​的作用。