There is a drop in stress indicating the system can not relax back to its equilibrium state because the maximum force barrier needs to be overcome. In this region, the material is in a metastable state ending with a fracture. The stressstrain curve shows that the ultimate stress in uniaxial strain (U ) is higher than that for biaxial strain (U ) in all three monolayers (Table ). This result also supports the higher influence of the biaxial strain as mentioned above. In addition, the higher value of ultimate stress of CrS 2 indicates that a larger force is needed to break it as compared to other monolayers.