Crack initiation at interface edge by nanometer scale plastic stress intensity

In order to investigate the crack initiation from the interface edge caused by nanometer scale plastic stress intensity, we conduct in situ mechanical bending experiments by using nano-cantilever specimens. The large-scale yielding (LSY) condition is successfully established in all nano-cantilever specimens, and fully plastic deformation governs the region near the interface edge where the crack initiates. The results show that, under the LSY condition, the stress distribution near the interface edge possesses the r-λP-type singularity with the same λP=0.14 among all specimens. An extremely small plastic singular stress field of only 13 nm is experimentally yielded, within which the critical plastic stress intensity parameter is approximately determined as KPC = 82 MPa m0.14. This indicates that the plastic singular stress field of 13 nm still governs the crack initiation from the interface edge, indicating the validity of the conventional fracture mechanics at such a nanometer scale.