Supercrystalline nanocomposites are a new class of hybrid and nanostructured materials that can reach exceptional mechanical strength and can be fabricated at low temperatures. Hierarchically arranged, they bridge the gap from the nano- to the macro-scale. Even though their mechanical properties are starting to be characterized, their constitutive behavior is still largely unexplored. Here, the mechanical behavior of supercrystalline nanocomposites of iron oxide nanoparticles, surface-functionalized with oleic acid and oleyl phosphate ligands, is investigated in both bending and compression, with loading–unloading tests. A new bar geometry is implemented to better detect deformation prior to unstable crack propagation, and notched bending bars are tested to evaluate fracture toughness. Micro-mechanical tests result in the values of strength and elastic modulus that are extremely high for supercrystals, reaching record-high numbers in the oleic acid-based nanocomposites, which also show a significant tension–compression asymmetry. The constitutive behavior of both materials is predominantly linear elastic, with some more marked nonlinearities arising in the oleyl phosphate-based nanocomposites. The fracture toughness of both types of nanocomposites, ∼0.3 MPa√m, suggests that extrinsic toughening, associated with both material composition and nanostructure, plays an important role. Fractographic observations reveal analogies with shear and cleavage in atomic crystals. The influence of material composition, nanostructure, and processing method on the mechanical behavior of the nanocomposites is analyzed.

中文翻译：

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超强超晶纳米复合材料的本构和断裂行为

超晶纳米复合材料是一类新型的混合纳米结构材料，可以达到卓越的机械强度，并且可以在低温下制造。它们按层次排列，弥合了从纳米尺度到宏观尺度的差距。尽管它们的机械性能开始被表征，但它们的本构行为在很大程度上仍未得到探索。在这里，用油酸和油基磷酸酯配体进行表面功能化的氧化铁纳米颗粒的超晶纳米复合材料的力学行为在弯曲和压缩以及加载-卸载测试中进行了研究。实施新的钢筋几何形状以在不稳定的裂纹扩展之前更好地检测变形，并测试带缺口的弯曲钢筋以评估断裂韧性。微机械测试导致超晶的强度和弹性模量值极高，在油酸基纳米复合材料中达到创纪录的高值，这也显示出显着的拉压不对称性。两种材料的本构行为主要是线弹性的，在基于磷酸油酯的纳米复合材料中出现了一些更明显的非线性。两种类型的纳米复合材料的断裂韧性约为 0.3 MPa√m，表明与材料成分和纳米结构相关的外在增韧起着重要作用。断口观察揭示了与原子晶体中的剪切和解理的类比。分析了材料组成、纳米结构和加工方法对纳米复合材料力学行为的影响。