Molecular dynamics study on tensile behavior of SiC nanofiber/C/SiC nanocomposites

Fracture behavior and mechanical properties of SiC nanofiber (SiC < inf > NF < /inf > ) reinforced SiC nanocomposites as influenced by the thickness of amorphous carbon (a-C) coatings are studied via molecular dynamics simulations using Tersoff potential. To simulate the condition that a matrix crack arrives at the interface between matrix and coating, a presetting matrix crack is created. Results show that the tensile stress-strain curve of nanocomposites without and/or with thin a-C coatings (e.g., t ≤ 0.3 nm) demonstrates an abrupt drop after achieving a maximum value, while nonlinear tails appear in the curves of nanocomposites with thick a-C coatings (e.g., t > 2.0 nm). It is demonstrated that the SiC < inf > NF < /inf > is penetrated by the matrix crack when it is uncoated and/or coated by a thin a-C layer (t ≤ 0.3 nm) and the nanocomposite fails in a typical brittle mode; whereas the crack deflection path changes and the SiC < inf > NF < /inf > is pulled out from the matrix when the a-C coatings are thick enough (e.g., 4 nm), showing a different fracture mode in nanocomposites. Compared to nanocomposites without an a-C coating, the tensile strength of nanocomposites with a-C coating of 4.0 nm thickness is about four times higher, and the fracture energy increases around an order of magnitude. Furthermore, the average stress concentration factor for SiC < inf > NF < /inf > in nanocomposites, defined as the ratio of tensile strength of single SiC < inf > NF < /inf > to the average stress of the nanofiber in the composite when it is broken, is extracted and shows a decreasing trend with increasing coating thickness, indicating that a-C coating can therefore be expected to simultaneously enhance the tensile strength and fracture energy of the SiC < inf > NF < /inf > /SiC nanocomposites. This work sheds light on the toughening mechanism in SiC < inf > NF &l