Knitting interloops one-dimensional yarns into three-dimensional fabrics that exhibit behaviours beyond their constitutive materials. How extensibility and anisotropy emerge from the hierarchical organization of yarns into knitted fabrics has long been unresolved. We sought to unravel the mechanical roles of tensile mechanics, assembly and dynamics arising from the yarn level on fabric nonlinearity by developing a yarn-based dynamical model. This physically validated model captures the fundamental mechanical response of knitted fabrics, analogous to flexible metamaterials and biological fiber networks due to geometric nonlinearity within such hierarchical systems. We identify the dictating factors of the mechanics of knitted fabrics, highlighting the previously overlooked but critical effect of pre-tension. Fabric anisotropy originates from observed yarn--yarn rearrangements during alignment dynamics and is topology-dependent. This yarn-based model also provides design flexibility of knitted fabrics to embed functionalities by allowing variation in both geometric configuration and material property. Our hierarchical approach to build up a knitted fabrics computationally modernizes an ancient craft and represents a first step towards mechanical programmability of knitted fabrics in wide engineering applications.

翻译：针织工艺将一维纱线互锁成三维织物，其表现出的行为超越了构成材料的本身特性。纱线如何通过层级组织结构赋予针织物延展性和各向异性这一长期悬而未决的问题，我们通过建立基于纱线的动力学模型，系统揭示了拉伸力学、纱线层级组装与动力学对织物非线性力学性能的影响。该经物理验证的模型能捕捉针织物的基本力学响应，由于此类层级体系中几何非线性的存在，其行为与柔性超材料和生物纤维网络具有相似性。我们识别出调控针织物力学的决定性因素，并强调了此前被忽视但至关重要的预张力效应。织物各向异性源于定向动力学过程中观测到的纱线间重排现象，且具有拓扑依赖性。这种基于纱线的模型通过允许几何构型与材料属性的双重变化，为针织物嵌入功能化设计提供了灵活性。我们的层级化计算方法将古老手工艺进行了数字化革新，标志着向实现针织物在广泛工程应用中力学可编程性迈出了第一步。