Propaedeutical to a better understanding of the mechanics of cables, with potential applications in material science and biology, tensile tests were performed on two-ply yarns made of rubber rods, manufactured by transforming the twist on two adjacent straight rods into tortuosity for the resulting double-helix shape. Modeling of the yarn as a pair of Kirchhoff rods in reciprocal contact, fails to provide results in agreement with experiments, especially when the helix slope angle tends to , representing the geometric limit for material interpenetration. This discrepancy could not be justified by considering the viscosity of the rods, their cross-sectional distortion, or cohesive/frictional contact. Our contribution starts from the experimental observation that the rods are in an eigenstress state already in the reference balanced configuration. This is characterized by a high twist, dictated by the ratio between torsional and bending rod stiffness, which increases as decreases, growing unboundedly as . Experiments confirm that twisting can significantly increase the tensile stiffness of straight rubber rods, in agreement with non-linear elasticity theory. Tensile tests on the yarns can be reproduced excellently only if the twist-induced stiffening is considered.

中文翻译：

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两股纱线特征应力状态及其对拉伸性能影响的实验评估

为了更好地理解电缆的力学原理，在材料科学和生物学方面具有潜在的应用，对由橡胶棒制成的两股纱线进行了拉伸测试，通过将两个相邻直棒上的捻度转化为由此产生的双股的曲折度来制造。 -螺旋形状。将纱线建模为一对相互接触的基尔霍夫杆，无法提供与实验一致的结果，特别是当螺旋斜角趋于 时，代表材料相互渗透的几何极限。通过考虑棒的粘度、其横截面变形或内聚/摩擦接触，无法证明这种差异是合理的。我们的贡献始于实验观察，即杆已经处于参考平衡配置中的特征应力状态。其特点是高扭转，由扭转杆刚度和弯曲杆刚度之间的比率决定，随着减小而增加，随着 的无限增长。实验证实，扭转可以显着提高直橡胶棒的拉伸刚度，这与非线性弹性理论一致。只有考虑加捻引起的硬化，才能很好地再现纱线的拉伸测试。