蜘蛛丝纤维中的塑性、迟滞和恢复机制
Plasticity, hysteresis, and recovery mechanisms in spider silk fibers
AI总结：
研究通过微观结构演变解释了蜘蛛丝在循环加载下的迟滞和恢复机制，提出了一种能量基模型，用于预测合成纤维的机械性能。
摘要：
蜘蛛丝是一种具有卓越刚度、强度和韧性的生物材料，源于其独特的微观结构。尽管最近的研究表明，丝纤维在循环加载下表现出塑性、迟滞和恢复特性，但其背后的微观机制尚未完全理解。在本工作中，我们提出了一种通过微观结构演变解释加载-卸载-松弛响应的机制：初始加载会扭曲分子间键，导致线性弹性区域。当达到屈服应力时，这些键断裂，外部载荷转移到多肽链上，这些链通过熵变允许大变形。卸载由熵变缩短驱动，直到达到无牵引力状态并具有残余伸长。随后，纤维恢复，因为链重新排列并键重新形成，将微观结构锁定在新的稳定平衡中，从而在后续循环中增加刚度。根据这些机制，我们开发了一个微观驱动、基于能量的模型，能够捕捉丝纤维在循环加载下的宏观响应。该响应被分解为两个并行网络：（1）一个由分子间和分子内键组成的弹塑性网络，控制初始刚度和屈服应力；（2）一个由熵变链组成的弹性网络，使纤维能够产生大变形。该模型通过Argiope bruennichi拖线丝的实验数据进行了验证。本工作得出的结论有三方面：（1）解释迟滞和恢复的机制，并将其与微观结构演变联系起来；（2）量化纤维的恢复过程，使其恢复并增强机械性能；（3）建立一个预测基础，用于工程定制性能的合成纤维。
英文摘要：
Spider silk is a remarkable biomaterial with exceptional stiffness, strength, and toughness stemming from a unique microstructure. While recent studies show that silk fibers exhibit plasticity, hysteresis, and recovery under cyclic loading, the underlying microstructural mechanisms are not yet fully understood. In this work, we propose a mechanism explaining the loading-unloading-relaxation response through microstructural evolution: initial loading distorts intermolecular bonds, resulting in a linear elastic regime. Upon reaching the yield stress, these bonds dissociate and the external load is transferred to the polypeptide chains, which deform entropically to allow large deformations. Unloading is driven by entropic shortening until a traction free state with residual stretch is achieved. Subsequently, the fiber recovers as chains reorganize and bonds reform, locking the microstructure into a new stable equilibrium that increases stiffness in subsequent cycles. Following these mechanisms, we develop a microscopically motivated, energy-based model that captures the macroscopic response of silk fibers under cyclic loading. The response is decoupled into two parallel networks: (1) an elasto-plastic network of inter- and intramolecular bonds governing the initial stiffness and yield stress, and (2) an elastic network of entropic chains that enable large deformations. The model is validated against experimental data from Argiope bruennichi dragline silk. The findings from this work are three-fold: (1) explaining the mechanisms that govern hysteresis and recovery and linking them to microstructural evolution; (2) quantifying the recovery process of the fiber, which restores and enhances mechanical properties; and (3) establishing a predictive foundation for engineering synthetic fibers with customized properties.
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