High fracture toughness in van der Waals-layered MoTe2: Disappearance of stress singularity

In this study, we demonstrated that van der Waals-layered MoTe2 , where two-dimensional atomic layers are closely laminated by weak interactions, has higher fracture toughness in out-of-plane cracks than that in in-plane cracks owing to structural anisotropy. In situ electron microscopy fracture toughness tests were performed on micro-sized specimens. The apparent fracture toughness of the out-of-plane crack based on the continuum assumption was approximately twice that of the in-plane crack. In the out-of-plane crack specimen, as the loading progressed, inter -laminar slip occurred between layers, and this discrete nature caused the stress singularity to disappear, leading to high fracture toughness.