Mechanics – Microstructure relations in 1D, 2D and mixed dimensional carbon nanomaterials

Utilizing 1D and 2D carbon nanomaterials to develop resilient and strong multifunctional composites has been a common theme in the field of nanomaterials in the past two decades. This theme is partly driven by the strong bonds between carbon atoms and the variety in bonding which translates into a wide variety of carbon nanomaterial types. It was once envisioned that CNT yarns would replace carbon fibers (CFs), an industry's gold standard for load bearing. However, the dream of developing super-strong materials based on carbon nanomaterials is yet to be fulfilled. In this paper, we have systematically reviewed the strength, fracture and failure mechanisms of 1D, including carbon nanotubes and carbon nanofibers, and 2D carbon materials, mainly graphene. For any physical quantity including strength, the measured values and the measurement techniques/protocols are inherently coupled. Therefore, the experimental approaches and the reported mechanical properties are reviewed together to assist with a better understanding of the true and engineering mechanical properties. The factors which limit strength and cause failure, especially the inevitable defects commonly observed in both 1D and 2D carbon nanomaterials, are discussed. Afterwards, the mixed dimensional carbon nanomaterials, where the 1D nanomaterials are used as reinforcement of 2D materials, is discussed towards developing super-tough structural materials. At the end, potential future research directions on carbon nanomaterials for load bearing is briefly discussed.