Basic structural units in carbon fibers: Atomistic models and tensile behavior

Understanding the atomistic mechanisms of tensile failure in carbon fibers is important for fiber manufacturing and applications. Here we design structural faults with atomistic details, pertaining to polyacrylonitrile (PAN) derived fibers, and probe them using large-scale molecular dynamics simulations to uncover trends and gain insight into the effect of local structure on the strength of the basic structural units (BSUs) and the role of interfaces between regions with different degrees of graphitization. Besides capturing the expected strength degrading with increasing misalignment, the designed basic structural units reveal atomistic details of local structural failure upon tensile loading. Fracture initiation is nearly always associated with the interface of the misoriented crystallite and its environment.