Atomistic Simulation of Crack Initiation at Bi-Material Interface Edges

Atomistic simulations using molecular dynamics (MD) method are conducted to check the conditions of the onset of fracture at the interface edges with a variety of angles. The simulations are facilitated with model bi-material systems interacting with Morse pair potentials. Three simulation models are considered, i.e. 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. And the onset of fracture at the interface edges with different geometries is controlled by the maximum stresses or the cohesive interfacial energy.

Molecular Dynamics Simulation on Crack Initiation at Bi-Material Interface Edges

Molecular dynamics (MD) simulations are performed to study the onset of fracture at the free edges of bi-material interfaces. The objective is to see whether a unified criterion could be formulated for crack initiation at interface edges with different angles or not. The simulations are facilitated with model bi-material systems interacting with Morse pair potentials. Three simulation models are considered, i.e. 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 revealed that the onset of fracture at the interface edges with different geometries could be controlled by the maximum stresses or the cohesive interfacial energy.

DYNAMICAL SCALING OF ANHARMONIC LATTICES AT THE ONSET OF FRACTURE

We investigate the dynamical renormalization properties of an anharmonic lattice. At the onset of fracture, we map this lattice into a transformed lattice with disorder. By studying the properties of the transformed lattice, we get analytical results for the dynamical scaling of the lattice. From these, we obtain the transformed memory of the lattice and we discuss how these results may be used to interpret simulations and experiments.

Origins of microplasticity in low-load scratching of silicon

Microstructural characterization of silicon wafers subjected to controlled low-load scratching with a sharp indenter reveals that considerable plastic deformation occurs prior to the onset of fracture. In particular, a completely ductile response to scratching is observed at or below a Vickers load of 1 g, corresponding to penetration depths of 200 nm or less. This anomalous plasticity arises primarily as a result of a pressure-induced semiconductor-to-metal phase transition (Mott transition). Various levels of subsurface dislocation activity and cracking also contribute to the deformation. The relationships among the phase transformation, dislocation activity, and the onset of fracture are discussed. These findings can be applied to other areas of contact damage demonstrating anomalous plasticity, such as hardness testing and ductile-regime turning.