Mechanics of Two‐Dimensional Materials

Over the past decade, two-dimensional (2D) crystals have been the focal point of nanoscience. Graphene, discovered in 2004, initiated the exploration of this field, with transition-metal dichalcogenides (TMDs) also garnering significant attention. The unique orbital symmetry within the honeycomb structure underpins various exceptional properties, spanning electrical, thermal, optical, and mechanical realms. Among the array of 2D materials, graphene, graphene oxide (GO), MoS 2 , and h -BN stand out as superstars, with extensive investigations into their properties and potential applications as next-generation materials. The mechanical analysis of 2D crystals not only elucidates potential applications but also unveils their distinctive mechanical behaviors. Numerous fields, including super-strong nanocomposites and flexible electronics, necessitate mechanical assessments of these crystals. Moreover, comprehending the nano-/micro-mechanisms governing deformation and fracture behavior in 2D crystals holds paramount importance in fundamental science. This chapter delves deeply into the mechanical characterizations-elasticity, fracture strength, fracture toughness, frictional behavior, and strain engineering-of graphene. Some of these mechanical assessments extend to other 2D crystals like graphene oxide, MoS 2 , and h -BN. Experimental measurements and theoretical calculations are compared, discussed, and summarized, revealing significant disparities across different techniques and simulations. For instance, while it's widely accepted that grain boundaries and initial cracks can weaken crystal strength, recent findings suggest that these factors, regardless of size, might not necessarily correlate with fracture strength. Given the ongoing debates surrounding the mechanical properties and behaviors of 2D crystals, coupled with the incomplete mechanical characterization of low-dimensional materials, there is a pressing need for more extensive and comprehensive studies to further our understanding of these novel and promising materials.