Catastrophic failure of materials and structures due to unstable crack growth could be prevented if fracture toughness could be enhanced at will through structural design, but how can this be possible if fracture toughness is a material constant related to energy dissipation in the vicinity of a propagating crack tip. Here we draw inspiration from the deformation behavior of biomolecules in load bearing biological materials, which have been evolved with a large extensibility and a high breaking strength beyond their elastic limit, and introduce an effective biomimetic strategy to enhance fracture toughness of a structure through an intrinsic to extrinsic (ITE) transition. In the ITE transition, toughness starts as an intrinsic parameter at the basic material level, but by designing a protein-like effective stress–strain behavior the toughness at the system level becomes an extrinsic parameter that increases with the system size without bound. This phenomenon is demonstrated through a combination of numerical simulations, analytic modeling and experiments, and leads to a biomimetic strategy which can be broadly adopted to enhance fracture toughness in engineering systems.

如果可以通过结构设计任意提高断裂韧性，则可以防止由于裂纹扩展不稳定而造成的材料和结构的灾难性破坏，但是，如果断裂韧性是与扩展裂纹附近的能量耗散有关的材料常数，怎么可能呢？小费。在这里，我们从具有负载能力的生物材料中生物分子的变形行为中汲取灵感，这些材料具有很大的扩展性和超过其弹性极限的高断裂强度，并提出了一种有效的仿生策略，以通过固有的方式增强结构的断裂韧性向外部（ITE）过渡。在ITE过渡中，韧性从基本材料级别开始作为内在参数，但是通过设计类似蛋白质的有效应力-应变行为，系统级的韧性成为外部参数，随系统大小的增加而不受限制。通过数值模拟，分析模型和实验的结合证明了这种现象，并导致了仿生策略，可以广泛采用该策略来提高工程系统的断裂韧性。