Despite promising applications of two-dimensional (2D) materials, one major concern is their propensity to fail in a brittle manner, which results in a low fracture toughness causing reliability issues in practical applications. We show that this limitation can be overcome by using functionalized graphene multilayers with fracture toughness (J integral) as high as ~39 J/m², measured via a microelectromechanical systems-based in situ transmission electron microscopy technique coupled with nonlinear finite element fracture analysis. The measured fracture toughness of functionalized graphene multilayers is more than two times higher than graphene (~16 J/m²). A linear fracture analysis, similar to that previously applied to other 2D materials, was also conducted and found to be inaccurate due to the nonlinear nature of the stress-strain response of functionalized graphene multilayers. A crack arresting mechanism of functionalized graphene multilayers was experimentally observed and identified as the main contributing factor for the higher fracture toughness as compared to graphene. Molecular dynamics simulations revealed that the interactions among functionalized atoms in constituent layers and distinct fracture pathways in individual layers, due to a random distribution of functionalized carbon atoms in multilayers, restrict the growth of a preexisting crack. The results inspire potential strategies for overcoming the relatively low fracture toughness of 2D materials through chemical functionalization.

中文翻译：

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功能化石墨烯多层材料的非线性断裂韧性测量和抗裂纹扩展性能。

尽管二维（2D）材料的应用前景广阔，但主要的担忧是它们以脆性方式失效的倾向，这导致较低的断裂韧性，从而在实际应用中引起可靠性问题。我们表明可以通过使用断裂韧性（J积分）高达〜39 J / m ^2的功能化石墨烯多层材料，通过基于微机电系统的原位透射电子显微镜技术与非线性有限元断裂分析相结合来测量，来克服这一局限性。测得的功能化石墨烯多层的断裂韧性是石墨烯的两倍以上（〜16 J / m ²）。还进行了类似于先前应用于其他2D材料的线性断裂分析，由于功能化石墨烯多层的应力-应变响应具有非线性特性，因此发现其不准确。实验观察到功能化石墨烯多层的裂纹阻止机制，并被认为是与石墨烯相比具有更高断裂韧性的主要因素。分子动力学模拟表明，由于多层中官能化碳原子的随机分布，构成层中的官能化原子与各个层中不同的断裂路径之间的相互作用限制了预先存在的裂纹的扩展。