尚福林 教授 特別講演会

This talk reviews the recent research results on interfacial crack initiation by atomistic simulations obtained from our group. Two parts of works are included: (1) critical conditions of crack nucleation at interface edges; (2) connections between crack nucleation at interface edges and crack growth along interface.

First of all, the simulation method and models are introduced. We use the so-called concurrent multiscale models combining the atomistic and continuum regions. That is, classical molecular dynamics (MD) method describes the behaviors near crack tip or interface edge apexes, and finite element method (FEM) determines the deformation fields of the regions away from the tip or apexes. We select a model bi-material system that mimics weak interface between thin copper film and tungsten substrate as the simulation system. Experiments show that the interface typically delaminates from the edge apex and fractures in a brittle manner. Therefore, our simulation work concentrates on perfectly brittle fracture behaviors of the interface edges and interface crack, and the corresponding models are developed.

First part of the works starts with the three simulation models that relates to the interface edges with angles 45°, 90° and 135°, respectively. The simulation results show that, at the instant of crack initiation, the maximum stresses along the interfaces reach the ideal strength of the interface; also, the interface energies just decrease to below the value of the intrinsic cohesive energy of the interface. These findings indicate that the onset of fracture at the interface edges with different geometries could be controlled by the maximum stress or the cohesive interfacial energy.

Second part aims to reveal the correlations between the critical conditions for crack nucleation at the interface edges and that for crack growth along the interface. Another three simulation models are considered, i.e., two interface edges with geometries of 90°/90° and 90°/180° angles, and one interface crack. The simulations show that, at the instant of fracture initiation, the maximum stresses along the interfaces reach the ideal strength of the interface; also their interface energies just overcome the characteristic cohesive energy of the interface. Thus, it is revealed that the different fracture conditions for crack nucleation at the interface edges and that for crack growth along the interface could be correlated through either the ideal strength or the cohesive energy of the interface.