Strain-induced crystallisation (SIC) is the phenomenon of elastomers to experience a pronounced nonlinearity under large deformations of several hundred percentages of strain, which is advantageous for industrial applications due to the resulting positive properties such as increasing crack growth resistance and fatigue behaviour. The overall objective of the current study is the constitutive modelling of the material behaviour of natural rubber when stretched uniaxially. Initially, unfilled natural rubber is considered. Cyclic traction experiments in which crystallinity, elongation and stresses are simultaneously measured are found in the literature. The same vulcanisate is used to conduct additional experiments in the present laboratory. The experimental investigations focus on uniaxial tension tests, conducted with a variety of parameters such as time and stretch rate. The current work presents an approach to model the SIC phenomenon. The model considers thermoelasticity and crystallisation. The approach of the hybrid free energy is used to derive constitutive equations and to meet thermomechanical consistency. However, the effect of temperature is not the focus of the current work. Furthermore, the contribution of a mixing energy is represented in the free energy. The derivation of this mixing entropy is explained in detail by making use of different assumptions and approaches, e.g. the consideration of ideal mixtures. Here, a one-dimensional constitutive model for strain-crystallising rubber is developed, which can be extended with a micro-sphere approach (concept of representative directions) to a full thermodynamically consistent anisotropic model.

中文翻译：

---

天然橡胶中的应变诱导结晶：使用多相方法的材料行为的热力学一致模型

应变诱导结晶（SIC）是弹性体在几百个百分应变的大变形下会出现明显的非线性的现象，由于产生的积极特性（如增加的抗裂纹扩展性和疲劳性能），这对工业应用是有利的。当前研究的总体目标是单轴拉伸时天然橡胶材料性能的本构模型。最初，考虑未填充的天然橡胶。在文献中发现了同时测量结晶度，伸长率和应力的循环牵引实验。在本实验室中，使用相同的硫化橡胶进行其他实验。实验研究集中在单轴拉伸试验上，使用各种参数（例如时间和拉伸率）进行。当前的工作提出了一种模拟SIC现象的方法。该模型考虑了热弹性和结晶。混合自由能的方法用于导出本构方程并满足热力学一致性。但是，温度的影响不是当前工作的重点。此外，混合能的贡献以自由能表示。通过使用不同的假设和方法（例如，考虑理想混合物）详细解释了混合熵的推导。在此，建立了应变结晶橡胶的一维本构模型，